800 East 96th Street, Indianapolis, Indiana, 46240 USA
James Foxall
SamsTeachYourself
24 in Hours
Visual
Basic 2010
Sams Teach Yourself Visual Basic 2010 in 24 Hours Complete Starter Kit
Copyright © 2010 by Pearson Education, Inc.
All rights reserved. No part of this book shall be reproduced, stored in a retrieval system, or
transmitted by any means, electronic, mechanical, photocopying, recording, or otherwise, without
written permission from the publisher. No patent liability is assumed with respect to the use of
the information contained herein. Although every precaution has been taken in the preparation of
this book, the publisher and author assume no responsibility for errors or omissions. Nor is any
liability assumed for damages resulting from the use of the information contained herein.
ISBN-13: 978-0-672-33113-8
ISBN-10: 0-672-33113-6
Library of Congress Cataloging-in-Publication Data:
Foxall, James D.
Sams teach yourself Visual Basic 2010 in 24 hours complete : starter kit / James Foxall.
p. cm.
Includes index.
ISBN 978-0-672-33113-8
1. Microsoft Visual BASIC. 2. BASIC (Computer program language) 3. Microsoft .NET. I. Title.
QA76.73.B3F69529 2010
006.7'882--dc22
2010011612
Printed in the United States on America
First Printing May 2010
Trademarks
All terms mentioned in this book that are known to be trademarks or service marks have been
appropriately capitalized. Sams Publishing cannot attest to the accuracy of this information. Use
of a term in this book should not be regarded as affecting the validity of any trademark or service
mark.
Warning and Disclaimer
Every effort has been made to make this book as complete and as accurate as possible, but no
warranty or fitness is implied. The information provided is on an “as is” basis. The author and the
publisher shall have neither liability nor responsibility to any person or entity with respect to any
loss or damages arising from the information contained in this book or from the use of the DVD
or programs accompanying it.
Bulk Sales
Sams Publishing offers excellent discounts on this book when ordered in quantity for bulk
purchases or special sales. For more information, please contact
U.S. Corporate and Government Sales
1-800-382-3419
corpsales@pearsontechgroup.com
For sales outside of the U.S., please contact
International Sales
international@pearsoned.com
Editor-in-Chief
Karen Gettman
Executive Editor
Neil Rowe
Development Editor
Mark Renfrow
Managing Editor
Patrick Kanouse
Project Editor
Mandie Frank
Copy Editor
Margo Catts
Indexer
Ken Johnson
Proofreader
Leslie Joseph
Technical Editor
J. Boyd Nolan
Publishing
Coordinator
Cindy Teeters
Multimedia
Developer
Dan Scherf
Designer
Gary Adair
Composition
Mark Shirar
From the Library of Wow! eBook
Contents at a Glance
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
PART I The Visual Basic 2010 Environment
HOUR 1 Jumping in with Both Feet: A Visual Basic 2010 Programming Tour......5
2 Navigating Visual Basic 2010..................................................................29
3 Understanding Objects and Collections ..................................................57
4 Understanding Events ..............................................................................79
PART II Building a User Interface
5 Building Forms: The Basics ......................................................................95
6 Building Forms: Advanced Techniques..................................................117
7 Working with Traditional Controls........................................................145
8 Using Advanced Controls.......................................................................173
9 Adding Menus and Toolbars to Forms ..................................................195
PART III Making Things Happen—Programming
10 Creating and Calling Code Procedures .................................................217
11 Using Constants, Data Types, Variables, and Arrays............................237
12 Performing Arithmetic, String Manipulation, and Date/Time
Adjustments............................................................................................269
13 Making Decisions in Visual Basic Code ................................................293
14 Looping for Efficiency ............................................................................309
15 Debugging Your Code ............................................................................323
16 Designing Objects Using Classes ...........................................................347
17 Interacting with Users ............................................................................367
18 Working with Graphics ..........................................................................389
PART IV Working with Data
19 Performing File Operations....................................................................409
20 Working with the Registry and Text Files..............................................427
21 Working with a Database ......................................................................451
22 Controlling Other Applications Using Automation..............................469
PART V Deploying Solutions and Beyond
23 Deploying Applications .........................................................................481
24 The 10,000-Foot View.............................................................................491
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 499
Table of Contents
Introduction 1
PART I: The Visual Basic 2010 Environment
HOUR 1: Jumping in with Both Feet: A Visual Basic 2010 Programming Tour 5
Starting Visual Basic 2010 ....................................................................................6
Creating a New Project ..........................................................................................7
Understanding the Visual Studio 2010 Environment ........................................10
Changing the Characteristics of Objects ............................................................11
Adding Controls to a Form..................................................................................16
Designing an Interface ........................................................................................17
Writing the Code Behind an Interface................................................................21
Running a Project ................................................................................................25
HOUR 2: Navigating Visual Basic 2010 29
Using the Visual Basic 2010 Start Page ..............................................................30
Navigating and Customizing the Visual Basic Environment ............................32
Working with Toolbars ........................................................................................37
Adding Controls to a Form Using the Toolbox ..................................................38
Setting Object Properties Using the Properties Window ....................................40
Managing Projects ..............................................................................................45
A Quick-and-Dirty Programming Primer ..........................................................51
Getting Help ........................................................................................................53
HOUR 3: Understanding Objects and Collections 57
Understanding Objects ........................................................................................58
Understanding Properties ....................................................................................58
Understanding Methods ......................................................................................65
Building a Simple Object Example Project ........................................................67
Understanding Collections ..................................................................................72
Using the Object Browser ....................................................................................75
Contents
v
HOUR 4: Understanding Events 79
Understanding Event-Driven Programming ......................................................79
Building an Event Example Project ....................................................................87
Keeping Event Names Current ............................................................................92
PART II: Building a User Interface
HOUR 5: Building Forms: The Basics 95
Changing a Form’s Name ..................................................................................96
Changing a Form’s Appearance ........................................................................97
Showing and Hiding Forms ..............................................................................107
HOUR 6: Building Forms: Advanced Techniques 117
Working with Controls ......................................................................................117
Creating Topmost Nonmodal Windows............................................................134
Creating Transparent Forms..............................................................................134
Creating Scrollable Forms..................................................................................134
Creating MDI Forms ..........................................................................................136
Setting the Startup Form....................................................................................140
HOUR 7: Working with Traditional Controls 145
Displaying Static Text with the Label Control ................................................145
Allowing Users to Enter Text Using a Text Box ................................................146
Creating Buttons................................................................................................154
Creating Containers and Groups of Option Buttons........................................157
Displaying a List with the List Box ..................................................................161
Creating Drop-Down Lists Using the
Combo Box ........................................................................................................168
HOUR 8: Using Advanced Controls 173
Creating Timers ................................................................................................174
Creating Tabbed Dialog Boxes ..........................................................................177
Storing Pictures in an Image List Control ......................................................180
Building Enhanced Lists Using the List View Control ....................................182
Creating Hierarchical Lists Using the
Tree View Control ............................................................................................187
vi
Teach Yourself in 24 Hours
HOUR 9: Adding Menus and Toolbars to Forms 195
Building Menus..................................................................................................196
Using the Toolbar Control ................................................................................207
Creating a Status Bar ........................................................................................213
PART III: Making Things Happen—Programming
HOUR 10: Creating and Calling Code Procedures 217
Creating Visual Basic Code Modules ................................................................217
Writing Code Procedures ..................................................................................219
Calling Code Procedures....................................................................................225
Exiting Procedures ............................................................................................231
Avoiding Infinite Recursion ..............................................................................232
HOUR 11: Using Constants, Data Types, Variables, and Arrays 237
Understanding Data Types ................................................................................238
Defining and Using Constants ..........................................................................242
Declaring and Referencing Variables................................................................244
Working with Arrays..........................................................................................250
Determining Scope ............................................................................................254
Declaring Variables of Static Scope ..................................................................258
Naming Conventions ........................................................................................259
Using Variables in Your Picture Viewer Project ................................................261
HOUR 12: Performing Arithmetic, String Manipulation,
and Date/Time Adjustments 269
Performing Basic Arithmetic Operations with Visual Basic ............................270
Comparing Equalities ........................................................................................274
Understanding Boolean Logic ..........................................................................274
Manipulating Strings ........................................................................................278
Working with Dates and Times ........................................................................283
HOUR 13: Making Decisions in Visual Basic Code 293
Making Decisions Using If...Then ................................................................293
Branching Within a Procedure Using GoTo ......................................................304
Contents
vii
HOUR 14: Looping for Efficiency 309
Looping a Specific Number of Times Using For...Next ................................309
Using Do...Loop to Loop an Indeterminate Number of Times ......................315
HOUR 15: Debugging Your Code 323
Adding Comments to Your Code ......................................................................324
Identifying the Two Basic Types of Errors ........................................................326
Using Visual Basic’s Debugging Tools ..............................................................329
Writing an Error Handler Using Try...Catch...Finally ............................336
HOUR 16: Designing Objects Using Classes 347
Understanding Classes ......................................................................................348
Instantiating Objects from Classes....................................................................357
HOUR 17: Interacting with Users 367
Displaying Messages Using the MessageBox.Show() Function ......................367
Creating Custom Dialog Boxes ........................................................................373
Using InputBox() to Get Information from a User ........................................377
Interacting with the Keyboard ..........................................................................379
Using the Common Mouse Events ....................................................................382
HOUR 18: Working with Graphics 389
Understanding the Graphics Object ................................................................389
Working with Pens ............................................................................................392
Using System Colors ..........................................................................................393
Working with Rectangles ..................................................................................396
Drawing Shapes ................................................................................................397
Drawing Text......................................................................................................399
Persisting Graphics on a Form..........................................................................400
Building a Graphics Project Example ..............................................................400
PART IV: Working with Data
HOUR 19: Performing File Operations 409
Using the OpenFileDialog and SaveFileDialog Controls ............................409
Manipulating Files with the File Object..........................................................415
Manipulating Directories with the Directory Object ....................................424
HOUR 20: Working with the Registry and Text Files 427
Working with the Registry ................................................................................427
Reading and Writing Text Files ........................................................................439
HOUR 21: Working with a Database 451
Introducing ADO.NET ......................................................................................452
Manipulating Data............................................................................................456
HOUR 22: Controlling Other Applications Using Automation 469
Automating Microsoft Excel ..............................................................................470
Automating Microsoft Word..............................................................................475
PART V: Deploying Solutions and Beyond
HOUR 23: Deploying Applications 481
Understanding ClickOnce Technology ..............................................................481
Using the Publish Wizard to Create a ClickOnce Application ........................482
Testing Your Picture Viewer ClickOnce Install Program ..................................486
Uninstalling an Application You’ve Distributed ..............................................486
Setting Advanced Options for Creating ClickOnce Programs..........................488
HOUR 24: The 10,000-Foot View 491
The .NET Framework ........................................................................................491
Common Language Runtime............................................................................492
Microsoft Intermediate Language ....................................................................493
Namespaces ......................................................................................................494
Common Type System ......................................................................................496
Garbage Collection ............................................................................................496
Further Reading ................................................................................................497
Index 499
viii
Teach Yourself in 24 Hours
About the Author
James Foxall is president of Tigerpaw Software, Inc. (www.tigerpawsoftware.com), a
Bellevue, Nebraska, Microsoft Certified Partner specializing in software solutions for
technology providers. Tigerpaw’s award-winning business automation solution is
designed to automate contact management, marketing, service and repair, proposal
generation, inventory control, and purchasing. At the start of 2010, the current release
of Tigerpaw had more than 25,000 licensed users. Foxall’s experience in creating certified
Office-compatible software has made him an authority on application interface
and behavior standards of applications for the Microsoft Windows and Microsoft Office
environments.
Foxall has been writing commercial production Visual Basic code for more than 14
years. He’s the author of numerous books, including Practical Standards for Microsoft
Visual Basic and MCSD in a Nutshell: The Visual Basic Exams. He also has written articles
for Access-Office-VBA Advisor and Visual Basic Programmer’s Journal. Foxall has a bachelor’s
degree in management of information systems (MIS) and a master’s degree in
Business Administration (MBA). He is a Microsoft Certified Solution Developer and an
international speaker on programming technologies as well as business process
improvements. James enjoys spending time with his family, playing guitar, listening to
amazing bands, and playing computer games. You can reach him at
www.jamesfoxall.com.
Dedication
This book is dedicated to Neil Rowe, for allowing me to create the
book I have always envisioned.
Acknowledgments
I would like to thank all the great people at Sams for their input and hard work; this
book would not be possible without them!
We Want to Hear from You!
As the reader of this book, you are our most important critic and commentator. We
value your opinion and want to know what we’re doing right, what we could do better,
what areas you’d like to see us publish in, and any other words of wisdom you’re
willing to pass our way.
You can email or write me directly to let me know what you did or didn’t like about
this book—as well as what we can do to make our books stronger.
Please note that I cannot help you with technical problems related to the topic of this book, and
that due to the high volume of mail I receive, I might not be able to reply to every message.
When you write, please be sure to include this book’s title and author as well as your
name and phone or email address. I will carefully review your comments and share
them with the author and editors who worked on the book.
Email: consumer@samspublishing.com
Mail: Neil Rowe
Executive Editor
Sams Publishing
800 East 96th Street
Indianapolis, IN 46240 USA
Reader Services
Visit our website and register this book at www.samspublishing.com/register for convenient
access to any updates, downloads, or errata that might be available for this book.
Audience and Organization 1
Introduction
Visual Basic 2010 is Microsoft’s latest incarnation of the enormously popular Visual
Basic language, and it’s fundamentally different from the versions that came before
it. Visual Basic is more powerful and more capable than ever before, and its features
and functionality are on par with “higher-level” languages such as C++. One consequence
of this newfound power is added complexity. Gone are the days when you
could sit down with Visual Basic and the online Help and teach yourself what you
needed to know to create a functional program.
Audience and Organization
This book is targeted toward those who have little or no programming experience or
who might be picking up Visual Basic as a second language. The book has been
structured and written with a purpose: to get you productive as quickly as possible.
I’ve used my experiences in writing large commercial applications with Visual Basic
and teaching Visual Basic to create a book that I hope cuts through the fluff and
teaches you what you need to know. All too often, authors fall into the trap of focusing
on the technology rather than on the practical application of the technology. I’ve
worked hard to keep this book focused on teaching you practical skills that you can
apply immediately to a development project. Feel free to post your suggestions or
success stories at www.jamesfoxall.com/forums.
This book is divided into five parts, each of which focuses on a different aspect of
developing applications with Visual Basic. These parts generally follow the flow of
tasks you’ll perform as you begin creating your own programs with Visual Basic. I
recommend that you read them in the order in which they appear.
. Part I, “The Visual Basic 2010 Environment,” teaches you about the Visual
Basic environment, including how to navigate and access Visual Basic’s
numerous tools. In addition, you’ll learn about some key development concepts
such as objects, collections, and events.
. Part II, “Building a User Interface,” shows you how to build attractive and
functional user interfaces. In this part, you’ll learn about forms and controls—
the user interface elements such as text boxes and list boxes.
. Part III, “Making Things Happen: Programming,” teaches you the nuts and
bolts of Visual Basic 2010 programming—and there’s a lot to learn. You’ll dis-
2 Introduction
Watch
Out!
Did you
Know?
cover how to create modules and procedures, as well as how to store data, perform
loops, and make decisions in code. After you’ve learned the core programming
skills, you’ll move into object-oriented programming and
debugging applications.
. Part IV, “Working with Data,” introduces you to working with graphics, text
files, and programming databases and shows you how to automate external
applications such as Word and Excel. In addition, this part teaches you how to
manipulate a user’s file system and the Windows Registry.
. Part V, “Deploying Solutions and Beyond,” shows you how to distribute an
application that you’ve created to an end user’s computer. In Hour 24, “The
10,000-Foot View,” you’ll learn about Microsoft’s .NET initiative from a higher,
less-technical level.
Many readers of previous editions have taken the time to give me input on how to
make this book better. Overwhelmingly, I was asked to have examples that build on
the examples in the previous chapters. In this book, I have done that as much as
possible. Instead of learning concepts in isolated bits, you’ll be building a featurerich
Picture Viewer program throughout the course of this book. You’ll begin by
building the basic application. As you progress through the chapters, you’ll add
menus and toolbars to the program, build an Options dialog box, modify the program
to use the Windows Registry and a text file, and even build a setup program to
distribute the application to other users. I hope you find this approach beneficial in
that it enables you to learn the material in the context of building a real program.
Conventions Used in This Book
This book uses several design elements and conventions to help you prioritize and
reference the information it contains:
By the Way boxes provide useful sidebar information that you can read immediately
or circle back to without losing the flow of the topic at hand.
By the
Way
Did You Know? boxes highlight information that can make your Visual Basic programming
more effective.
Watch Out! boxes focus your attention on problems or side effects that can occur
in specific situations.
Onward and Upward! 3
New terms appear in an italic typeface for emphasis.
In addition, this book uses various typefaces to help you distinguish code from regular
English. Code is presented in a monospace font. Placeholders—words or characters
that represent the real words or characters you would type in code—appear in italic
monospace. When you are asked to type or enter text, that text appears in bold.
Menu options are separated by a comma. For example, when you should open the
File menu and choose the New Project menu option, the text says “Select File, New
Project.”
Some code statements presented in this book are too long to appear on a single line.
In these cases, a line-continuation character (an underscore) is used to indicate that
the following line is a continuation of the current statement.
Onward and Upward!
This is an exciting time to be learning how to program. It’s my sincerest wish that
when you finish this book, you feel capable of using many of Visual Basic’s tools to
create, debug, and deploy modest Visual Basic programs. Although you won’t be an
expert, you’ll be surprised at how much you’ve learned. And I hope this book will
help you determine your future direction as you proceed down the road to Visual
Basic mastery.
I love programming with Visual Basic, and sometimes I find it hard to believe I get
paid to do so. I hope you find Visual Basic as enjoyable as I do!
This page intentionally left blank
5
HOUR 1
Jumping in with Both Feet:
A Visual Basic 2010
Programming Tour
What You’ll Learn in This Hour:
. Building a simple (yet functional) Visual Basic application
. Letting a user browse a hard drive
. Displaying a picture from a file on disk
. Getting familiar with some programming lingo
. Learning about the Visual Studio 2010 IDE
Learning a new programming language can be intimidating. If you’ve never programmed
before, the act of typing seemingly cryptic text to produce sleek and powerful
applications probably seems like a black art, and you might wonder how you’ll
ever learn everything you need to know. The answer, of course, is one step at a time.
I believe the first step to mastering a programming language is building confidence.
Programming is part art and part science. Although it might seem like magic, it’s
more akin to illusion. After you know how things work, a lot of the mysticism goes
away, and you are free to focus on the mechanics necessary to produce the desired
result.
Producing large, commercial solutions is accomplished by way of a series of small
steps. After you’ve finished this hour, you’ll have a feel for the overall development
process and will have taken the first step toward becoming an accomplished programmer.
In fact, you will build on the examples in this hour in subsequent chapters.
By the time you complete this book, you will have built a robust application,
complete with resizable screens, an intuitive interface including menus and toolbars,
manipulation of the Windows Registry, and robust code with professional error handling.
But I’m getting ahead of myself.
6 HOUR 1: Jumping in with Both Feet: A Visual Basic 2010 Programming Tour
By the
Way In the past, Visual Basic was an autonomous language. This has changed. Now,
Visual Basic is part of a larger entity known as the .NET Framework. The .NET
Framework encompasses all the .NET technology, including Visual Studio .NET
(the suite of development tools) and the common language runtime (CLR), which
is the set of files that make up the core of all .NET applications. You’ll learn about
these items in more detail as you progress through this book. For now, realize
that Visual Basic is one of many languages that exist within the Visual Studio
family. Many other languages, such as C#, are also .NET languages, make use of
the CLR, and are developed within Visual Studio.
In this hour, you’ll complete a quick tour of Visual Basic that takes you step by step
through creating a complete, albeit small, Visual Basic program. Most introductory
programming books start by having the reader create a simple Hello World program.
I’ve yet to see a Hello World program that’s the least bit helpful. (They usually do
nothing more than print hello world to the screen—what fun!) So, instead, you’ll
create a Picture Viewer application that lets you view Windows bitmaps and icons on
your computer. You’ll learn how to let a user browse for a file and how to display a
selected picture file on the screen. The techniques you learn in this chapter will come
in handy in many real-world applications that you’ll create, but the goal of this chapter
is for you to realize just how much fun it is to program using Visual Basic 2010.
Starting Visual Basic 2010
Before you begin creating programs in Visual Basic 2010, you should be familiar
with the following terms:
. Distributable component: The final, compiled version of a project. Components
can be distributed to other people and other computers, and they don’t
require the Visual Basic 2010 development environment (the tools you use to
create a .NET program) to run (although they do require the .NET runtime,
which I’ll discuss in Hour 23, “Deploying Applications”). Distributable components
are often called programs. In Hour 23, you’ll learn how to distribute the
Picture Viewer program that you’re about to build to other computers.
. Project: A collection of files that can be compiled to create a distributable
component (program). There are many types of projects, and complex applications
might consist of multiple projects, such as Windows application projects
and support dynamic link library (DLL) projects.
. Solution: A collection of projects and files that make up an application or
component.
Creating a New Project 7
Visual Studio 2010 is a complete development environment, and it’s called the IDE
(short for integrated development environment). The IDE is the design framework in
which you build applications; every tool you’ll need to create your Visual Basic projects
is accessed from within the Visual Basic IDE. Again, Visual Studio 2010 supports
development using many different languages, Visual Basic being the most popular.
The environment itself is not Visual Basic, but the language you’ll be using within
Visual Studio 2010 is Visual Basic. To work with Visual Basic projects, you first start
the Visual Studio 2010 IDE.
Start Visual Studio 2010 now by choosing Microsoft Visual Basic 2010 Express Edition
from the Start/Programs menu. If you are running the full retail version of Visual Studio,
your shortcut may have a different name. In this case, locate the shortcut on the
Start menu and click it once to start the Visual Studio 2010 IDE.
Creating a New Project
When you first start Visual Studio 2010, you see the Start Page tab within the IDE, as
shown in Figure 1.1. You can open projects created previously or create new projects
from this Start page. For this quick tour, you’ll create a new Windows application, so
select File, New Project to display the New Project dialog box shown in Figure 1.2.
FIGURE 1.1
You can open
existing projects
or create new
projects from the
Visual Studio
Start page.
8 HOUR 1: Jumping in with Both Feet: A Visual Basic 2010 Programming Tour
If your Start page doesn’t look like the one shown in Figure 1.1, chances are that
you’ve changed the default settings. In Hour 2, “Navigating Visual Basic 2010,”
I’ll show you how to change them back.
By the
Way
The New Project dialog box is used to specify the type of Visual Basic project to create.
(You can create many types of projects with Visual Basic, as well as with the other
supported languages of the .NET Framework.) The options shown in Figure 1.2 are
limited because I am running the Express edition of Visual Basic for all examples in
this book. If you are running the full version of Visual Studio, you will have many
more options available.
Create a new Windows Forms Application now by following these steps:
1. Make sure that the Windows Forms Application item is selected. (If it’s not, click
it once to select it.)
2. At the bottom of the New Project dialog box is a Name text box. This is where,
oddly enough, you specify the name of the project you’re creating. Enter
Picture Viewer in the Name text box.
3. Click OK to create the project.
Always set the Name text box to something meaningful before creating a project,
or you’ll have more work to do later if you want to move or rename the project.
Did you
Know?
FIGURE 1.2
The New Project
dialog box
enables you to
create many
types of .NET
projects.
Creating a New Project 9
When Visual Basic creates a new Windows Forms Application project, it adds one
form (the empty gray window) for you to begin building the interface for your application,
as shown in Figure 1.3.
Within Visual Studio 2010, form is the term given to the design-time view of a
window that can be displayed to a user.
By the
Way
Your Visual Studio 2010 environment might look different from that shown in the figures
in this hour, depending on the edition of Visual Studio 2010 you’re using,
whether you’ve already played with Visual Studio 2010, and other factors, such as
your monitor’s resolution. All the elements discussed in this hour exist in all editions
of Visual Studio 2010, however. (If a window shown in a figure doesn’t appear in your
IDE, use the View menu to display it.)
To create a program that can be run on another computer, you start by creating a
project and then compiling the project into a component such as an executable (a
program a user can run) or a DLL (a component that can be used by other programs
and components). The compilation process is discussed in detail in Hour
23. The important thing to note at this time is that when you hear someone refer
to creating or writing a program, just as you’re creating the Picture Viewer program
now, that person is referring to the completion of all steps up to and including
compiling the project to a distributable file.
By the
Way
FIGURE 1.3
New Windows
Forms Applications
start with a
blank form; the
fun is just beginning!
10 HOUR 1: Jumping in with Both Feet: A Visual Basic 2010 Programming Tour
Understanding the Visual Studio 2010
Environment
The first time you run Visual Studio 2010, you’ll notice that the IDE contains a number
of windows, such as the Properties window on the right, which is used to view and
set properties of objects. In addition to these windows, the IDE contains a number of
tabs, such as the vertical Toolbox tab on the left edge of the IDE (refer to Figure 1.3).
Try this now: Click the Toolbox tab to display the Toolbox window (clicking a tab displays
an associated window). You can hover the mouse over a tab for a few seconds
to display the window as well. To hide the window, simply move the mouse off the
window (if you hovered over the tab to display it) or click another window. To close
the window, click the Close (X) button in the window’s title bar.
If you opened the toolbox by clicking its tab rather than hovering over the tab, the
toolbox does not close automatically. Instead, it stays open until you click another
window.
By the
Way
You can adjust the size and position of any of these windows, and you can even hide
and show them as needed. You’ll learn how to customize your design environment in
Hour 2.
Unless specifically instructed to do so, don’t double-click anything in the Visual
Studio 2010 design environment. Double-clicking most objects produces an
entirely different result than single-clicking does. If you mistakenly double-click an
object on a form (discussed shortly), a code window appears. At the top of the
code window is a set of tabs: one for the form design and one for the code. Click
the tab for the form design to hide the code window and return to the form.
Watch
Out!
The Properties window on the right side of the design environment is perhaps the
most important window in the IDE, and it’s the one you’ll use most often. If your
computer display resolution is set to 800×600, you can probably see only a few properties
at this time. This makes it difficult to view and set properties as you create projects.
All the screen shots in this book were captured on Windows 7 running at
800×600 because of size constraints, but you should run at a higher resolution if you
can. I highly recommend that you develop applications with Visual Basic at a screen
resolution of 1024×768 or higher to have plenty of work space. To change your display
settings, right-click the desktop and select Screen Resolution. Keep in mind, however,
that end users might be running at a lower resolution than you are using for
development.
Changing the Characteristics of Objects 11
You’ll find that I often mention material coming up in future chapters. In the publishing
field, we call these forward references. For some reason, these tend to
unnerve some people. I do this only so that you realize you don’t have to fully
grasp a subject when it’s first presented; the material will be covered in more
detail later. I try to keep forward references to a minimum, but unfortunately,
teaching programming is not a perfectly linear process. There will be times I’ll
have to touch on a subject that I feel you’re not ready to dive into fully yet. When
this happens, I give you a forward reference to let you know that the subject will
be covered in greater detail later.
Watch
Out!
Every object has a distinct set of attributes known as properties (regardless of whether
the object has a physical appearance). Properties define an object’s characteristics.
You have certain properties, such as your height and hair color. Visual Basic objects
have properties as well, such as Height and BackColor. When you create a new
object, the first thing you need to do is set its properties so that the object appears and
behaves the way you want it to. To display an object’s properties, click the object in its
designer (the main work area in the IDE).
Click anywhere in the default form now, and check to see that its properties are displayed
in the Properties window. You’ll know because the drop-down list box at the
top of the Properties window contains the form’s name: Form1
System.Windows.Forms.Form. Form1 is the object’s name, and
System.Windows.Forms.Form is the object’s type.
Naming Objects
The property you should always set first when creating any new object is the Name
property. Press F4 to display the Properties window (if it’s not already visible), and
scroll toward the top of the properties list until you see the (Name) property, as shown
in Figure 1.4. If the Name property isn’t one of the first properties listed, the Properties
Changing the Characteristics of Objects
Almost everything you work with in Visual Basic is an object. Forms, for instance, are
objects, as are all the items you can put on a form to build an interface, such as list
boxes and buttons. There are many types of objects, and objects are classified by type.
For example, a form is a Form object, whereas items you can place on a form are
called Control objects, or controls. (Hour 3, “Understanding Objects and Collections,”
discusses objects in detail.) Some objects don’t have a physical appearance but exist
only in code. You’ll learn about these kinds of objects in later hours.
12 HOUR 1: Jumping in with Both Feet: A Visual Basic 2010 Programming Tour
window is set to show properties categorically instead of alphabetically. You can show
the list alphabetically by clicking the Alphabetical button that appears just above the
properties grid.
I recommend that you keep the Properties window set to show properties in
alphabetical order; doing so makes it easier to find properties that I refer to in
the text. Note that the Name property always stays toward the top of the list and is
called (Name). If you’re wondering why it has parentheses around it, it’s because
the parentheses force the property to the top of the list; symbols come before
letters in an alphabetical sort.
By the
Way
When saving a project, you choose a name and a location for the project and its files.
When you first create an object within the project, Visual Basic gives the object a
unique, generic name based on the object’s type. Although these names are functional,
they simply aren’t descriptive enough for practical use. For instance, Visual
Basic named your form Form1, but it’s common to have dozens (or even hundreds) of
forms in a project. It would be extremely difficult to manage such a project if all
forms were distinguishable only by a number (Form2, Form3, and so forth).
What you’re actually working with is a form class, or template, that will be used to
create and show forms at runtime. For the purposes of this quick tour, I simply
call it a form. See Hour 5, “Building Forms: The Basics,” for more information.
By the
Way
To better manage your forms, give each one a descriptive name. Visual Basic gives
you the chance to name new forms as they’re created in a project. Visual Basic created
this default form for you, so you didn’t get a chance to name it. It’s important
FIGURE 1.4
The Name property
is the first
property you
should change
when you add a
new object to
your project.
Changing the Characteristics of Objects 13
not only to change the form’s name but also to change its filename. Change the programmable
name and the filename by following these steps:
1. Click the Name property and change the text from Form1 to ViewerForm. Notice
that this does not change the form’s filename as it’s displayed in the Solution
Explorer window, located above the Properties window.
2. Right-click Form1.vb in the Solution Explorer window (the window above the
Properties window).
3. Choose Rename from the context menu that appears.
4. Change the text from Form1.vb to ViewerForm.vb.
I use the Form suffix here to denote that the file is a form class. Suffixes are
optional, but I find that they really help you keep things organized.
By the
Way
The form’s Name property is actually changed for you automatically when you
rename the file. In future examples, I will have you rename the form file so that the
Name property is changed automatically. I had you set it in the Properties window
here so that you could see how the Properties window works.
Setting the Form’s Text Property
Notice that the text that appears in the form’s title bar says Form1. Visual Basic sets
the form’s title bar to the name of the form when it’s first created, but doesn’t change it
when you change the name of the form. The text in the title bar is determined by the
value of the form’s Text property. Change the text now by following these steps:
1. Click the form once more so that its properties appear in the Properties window.
2. Use the scrollbar in the Properties window to locate the Text property.
3. Change the text to Picture Viewer. Press the Enter key or click a different property.
You’ll see the text in the form’s title bar change.
Saving a Project
The changes you’ve made so far exist only in memory. If you were to turn off your
computer at this time, you would lose all your work up to this point. Get into the
habit of frequently saving your work, which commits your changes to disk.
14 HOUR 1: Jumping in with Both Feet: A Visual Basic 2010 Programming Tour
The following instructions assume that you have access to the source files for the
examples in this book. They are available at http://www.samspublishing.com. You
can also get these files, as well as discuss this book, at my website at http:/
/www.jamesfoxall.com/books.aspx. When you unzip the samples, a folder is created
for each hour, and within each hour’s folder are subfolders for the sample
projects. You’ll find the icon for this example in the folder Hour 01\Picture Viewer.
You don’t have to use the icon I’ve provided for this example; you can use any
icon. If you don’t have an icon available (or you want to be a rebel), you can skip
this section without affecting the outcome of the example.
By the
Way
To give the form an icon, follow these steps:
1. In the Properties window, click the Icon property to select it.
2. When you click the Icon property, a small button with three dots appears to
the right of the property. Click this button.
FIGURE 1.5
When saving a
project, choose
a name and
location for the
project and its
files.
Click the Save All button on the toolbar (the picture of a stack of floppy disks) now to
save your work. Visual Basic displays the Save Project dialog box, shown in Figure
1.5. Notice that the Name property is already filled in because you named the project
when you created it. The Location text box is where you specify the location in which
the project is to be saved. Visual Basic creates a subfolder in this location, using the
value in the Name text box (in this case, Picture Viewer). You can use the default
location or change it to suit your purposes. You can have Visual Basic create a solution
folder, and if you do Visual Basic creates the solution file in the folder, and it creates
a subfolder for the project and the actual files. On large projects, this is a handy
feature. For now, it’s an unnecessary step, so uncheck the Create Directory for Solution
box and then click Save to save the project.
Giving the Form an Icon
Everyone who’s used Windows is familiar with icons—the little pictures that represent
programs. Icons most commonly appear on the Start menu next to the name of their
respective programs. In Visual Basic, not only do you have control over the icon of
your program file, but you also can give every form in your program a unique icon if
you want to.
Changing the Characteristics of Objects 15
3. Use the Open dialog box that appears to locate the Picture Viewer.ico file or
another icon file of your choice. When you’ve found the icon, double-click it, or
click it once to select it and then choose Open.
After you’ve selected the icon, it appears in the Icon property along with the word
Icon. A small version of the icon appears in the upper-left corner of the form as well.
Whenever this form is minimized, this is the icon displayed on the Windows taskbar.
Changing the Form’s Size
Next, you’ll change the form’s Width and Height properties. The Width and Height
values are shown collectively under the Size property; Width appears to the left of
the comma, and Height to the right. You can change the Width or Height property
by changing the corresponding number in the Size property. Both values are represented
in pixels. (That is, a form that has a Size property of 200, 350 is 200 pixels
wide and 350 pixels tall.) To display and adjust the Width and Height properties separately,
click the small triangle next to the Size property (see Figure 1.6). (After you
click it, it changes to a triangle pointing diagonally down.)
A pixel is a unit of measurement for computer displays; it’s the smallest visible
“dot” on the screen. The resolution of a display is always given in pixels, such as
800×600 or 1024×768. When you increase or decrease a property by one pixel,
you’re making the smallest possible visible change to the property.
By the
Way
Change the Width property to 400 and the Height to 325 by typing in the corresponding
box next to a property name. To commit a property change, press Tab or Enter,
FIGURE 1.6
Some properties
can be expanded
to show more
specific properties.
16 HOUR 1: Jumping in with Both Feet: A Visual Basic 2010 Programming Tour
or click a different property or window. Your screen should now look like the one
shown in Figure 1.7.
You can also size a form by dragging its border, which you’ll learn about in Hour 2,
or by using code to change its properties, which you’ll learn how to do in Hour 5.
By the
Way
Save the project now by choosing File, Save All from the menu or by clicking the Save
All button on the toolbar—it has a picture of stacked floppy disks.
Adding Controls to a Form
Now that you’ve set the initial properties of your form, it’s time to create a user interface
by adding objects to the form. Objects that can be placed on a form are called
controls. Some controls have a visible interface with which a user can interact,
whereas others are always invisible to the user. You’ll use controls of both types in this
example. On the left side of the screen is a vertical tab titled Toolbox. Click the Toolbox
tab to display the Toolbox window to see the most commonly used controls,
expanding the Common Controls section if necessary (see Figure1.8). The toolbox
contains all the controls available in the project, such as labels and text boxes.
FIGURE 1.7
Changes made
in the Properties
window are
reflected as
soon as they’re
committed.
Designing an Interface 17
FIGURE 1.8
The toolbox is
used to select
controls to build
a user interface.
The toolbox closes as soon as you’ve added a control to a form and when the pointer
is no longer over the toolbox. To make the toolbox stay visible, click the little picture
of a pushpin located in the toolbox’s title bar.
I don’t want you to add them yet, but your Picture Viewer interface will consist of the
following controls:
. Two Button controls: The standard buttons that you’re used to clicking in
pretty much every Windows program you’ve ever run
. A PictureBox control: A control used to display images to a user
. An OpenFileDialog control: A hidden control that exposes the Windows
Open File dialog box functionality
Designing an Interface
It’s generally best to design a form’s user interface and then add the code behind the
interface to make the form functional. You’ll build your interface in the following
sections.
18 HOUR 1: Jumping in with Both Feet: A Visual Basic 2010 Programming Tour
Adding a Visible Control to a Form
Start by adding a Button control to the form. Do this by double-clicking the Button
item in the toolbox. Visual Basic creates a new button and places it in the upper-left
corner of the form, as shown in Figure 1.9.
Using the Properties window, set the button’s properties as shown in the following list.
Remember, when you view the properties alphabetically, the Name property is listed
first, so don’t go looking for it down in the list or you’ll be looking a while.
Now you’ll create a button that the user can click to close the Picture Viewer program.
Although you could add another new button to the form by double-clicking the
Button control on the toolbox again, this time you’ll add a button to the form by creating
a copy of the button you’ve already defined. This enables you to easily create a
button that maintains the size and other style attributes of the original button when
the copy was made.
To do this, right-click the Select Picture button, and choose Copy from its context
menu. Next, right-click anywhere on the form, and choose Paste from the form’s
FIGURE 1.9
When you doubleclick
a control in
the toolbox, the
control is added
to the upper-left
corner of the
form.
Property Value
Name btnSelectPicture
Location 295,10 (295 is the x coordinate; 10 is the y coordinate.)
Size 85,23
Text Select Picture
Designing an Interface 19
shortcut menu. (You can also use the keyboard shortcuts Ctrl+C to copy and Ctrl+V to
paste.) The new button appears centered on the form, and it’s selected by default.
Notice that it retains almost all the properties of the original button, but the name
has been reset. Change the properties of the new button as follows:
The last visible control you need to add to the form is a PictureBox control. A
PictureBox has many capabilities, but its primary purpose is to show pictures, which
is precisely what you’ll use it for in this example. Add a new PictureBox control to
the form by double-clicking the PictureBox item in the toolbox, and set its properties
as follows:
After you’ve made these property changes, your form will look like the one shown in
Figure 1.10. Click the Save All button on the toolbar to save your work.
Property Value
Name btnQuit
Location 295,40
Text Quit
Property Value
Name picShowPicture
BorderStyle FixedSingle
Location 8,8
Size 282,275
FIGURE 1.10
An application’s
interface doesn’t
have to be
complex to be
useful.
20 HOUR 1: Jumping in with Both Feet: A Visual Basic 2010 Programming Tour
Other controls in addition to the OpenFileDialog control give you file functionality.
For example, the SaveFileDialog control provides features for allowing the
user to specify a filename and path for saving a file.
By the
Way
Display the toolbox and scroll down using the down arrow in the lower part of the
toolbox until you can see the OpenFileDialog control (it’s in the Dialogs category),
and then double-click it to add it to your form. Note that the control isn’t placed on
the form; rather, it appears in a special area below the form (see Figure 1.11). This
FIGURE 1.11
Controls that
have no interface
appear
below the form
designer.
Adding an Invisible Control to a Form
All the controls you’ve used so far sit on a form and have a physical appearance
when a user runs the application. Not all controls have a physical appearance, however.
Such controls, called nonvisual controls (or invisible-at-runtime controls), aren’t
designed for direct user interactivity. Instead, they’re designed to give you, the programmer,
functionality beyond the standard features of Visual Basic.
To enable users to select a picture to display, you need to give them the ability to
locate a file on their hard drives. You might have noticed that whenever you choose
to open a file from within any Windows application, the dialog box displayed is
almost always the same. It doesn’t make sense to force every developer to write the
code necessary to perform standard file operations, so Microsoft has exposed the
functionality via a control that you can use in your projects. This control is called
OpenFileDialog, and it will save you dozens of hours that would otherwise be necessary
to duplicate this common functionality.
Writing the Code Behind an Interface 21
happens because the OpenFileDialog control has no form interface to display to the
user. It does have an interface (a dialog box) that you can display as necessary, but it
has nothing to display directly on a form.
Select the OpenFileDialog control and change its properties as follows:
Don’t actually enter the text <make empty> for the filename; I really mean delete
the default value and make this property value empty.
By the
Way
The Filter property is used to limit the types of files that will be displayed in the
Open File dialog box. The format for a filter is description|filter. The text that appears
before the first pipe symbol is the descriptive text of the file type, whereas the text
after the pipe symbol is the pattern to use to filter files. You can specify more than one
filter type by separating each description|filter value with another pipe symbol. Text
entered into the Title property appears in the title bar of the Open File dialog box.
The graphical interface for your Picture Viewer program is now finished. If you
pinned the toolbox open, click the pushpin in the title bar of the toolbox now to close
it. Click Save All on the toolbar now to save your work.
Writing the Code Behind an Interface
You have to write code for the program to be capable of performing tasks and
responding to user interaction. Visual Basic is an event-driven language, which means
that code is executed in response to events. These events might come from users, such
as a user clicking a button and triggering its Click event, or from Windows itself (see
Hour 4, “Understanding Events,” for a complete explanation of events). Currently,
your application looks nice, but it won’t do anything. Users can click the Select Picture
button until they can file for disability with carpel tunnel syndrome, but nothing
will happen, because you haven’t told the program what to do when the user clicks
Property Value
Name ofdSelectPicture
Filename <make empty>
Filter Windows Bitmaps|*.BMP|JPEG Files|*.JPG
Title Select Picture
22 HOUR 1: Jumping in with Both Feet: A Visual Basic 2010 Programming Tour
the button. You can see this for yourself now by pressing F5 to run the project. Feel
free to click the buttons, but they don’t do anything. When you’re finished, close the
window you created to return to Design mode.
You’ll write code to accomplish two tasks. First, you’ll write code that lets users browse
their hard drives to locate and select a picture file and then display it in the picture
box (this sounds a lot harder than it is). Second, you’ll add code to the Quit button
that shuts down the program when the user clicks the button.
Letting a User Browse for a File
The first bit of code you’ll write enables users to browse their hard drives, select a picture
file, and then see the selected picture in the PictureBox control. This code executes
when the user clicks the Select Picture button; therefore, it’s added to the Click
event of that button.
When you double-click a control on a form in Design view, the default event for that
control is displayed in a code window. The default event for a Button control is its
Click event, which makes sense, because clicking is the most common action a user
performs with a button. Double-click the Select Picture button now to access its Click
event in the code window (see Figure 1.12).
When you access an event, Visual Basic builds an event handler, which is essentially a
template procedure in which you add the code that executes when the event occurs.
FIGURE 1.12
You’ll write all
your code in a
window such as
this.
Writing the Code Behind an Interface 23
After you insert the statement that begins with If and press Enter, Visual Basic
automatically creates the End If statement for you. If you type in End If, you’ll
wind up with two End If statements, and your code won’t run. If this happens,
delete one of the statements. Hour 13, “Making Decisions in Visual Basic Code,”
has all the details on the If statement.
By the
Way
It’s time for another comment. The cursor is currently between the statement that
starts with If and the End If statement. Leave the cursor there and type the following
statement, remembering to press Enter at the end of the line:
’ Load the picture into the picture box.
Don’t worry about indenting the code by pressing the Tab key or using spaces.
Visual Basic automatically indents code for you.
Did you
Know?
The cursor is already placed within the code procedure, so all you have to do is add
code. Although this may seem daunting, by the time you’re finished with this book,
you’ll be madly clicking and clacking away as you write your own code to make your
applications do exactly what you want them to do—well, most of the time. For now,
just enter the code as I present it here.
It’s important that you get in the habit of commenting your code, so the first statement
you’ll enter is a comment. Beginning a statement with an apostrophe (’) designates
that statement as a comment. The compiler won’t do anything with the
statement, so you can enter whatever text you want after the apostrophe. Type the following
statement exactly as it appears, and press the Enter key at the end of the line:
’ Show the open file dialog box.
The next statement you’ll enter triggers a method of the OpenFileDialog control that
you added to the form. Think of a method as a mechanism to make a control do
something. The ShowDialog() method tells the control to show its Open dialog box
and let the user select a file. The ShowDialog() method returns a value that indicates
its success or failure, which you’ll then compare to a predefined result
(DialogResult.OK). Don’t worry too much about what’s happening here; you’ll be
learning the details of all this in later hours. The sole purpose of this hour is to get
your feet wet. In a nutshell, the ShowDialog() method is invoked to let a user browse
for a file. If the user selects a file, more code is executed. Of course, there’s a lot more to
using the OpenFileDialog control than I present in this basic example, but this simple
statement gets the job done. Enter the following statement and press Enter to commit
the code (don’t worry about capitalization; Visual Basic will fix the case for you):
If ofdSelectpicture.ShowDialog = DialogResult.OK Then
24 HOUR 1: Jumping in with Both Feet: A Visual Basic 2010 Programming Tour
This next statement, which appears within the If construct (between the If and End
If statements), is the line of code that actually displays the picture in the picture box.
Enter the following statement:
picShowPicture.Image = Image.FromFile(ofdSelectPicture.Filename)
In addition to displaying the selected picture, your program also displays the path
and filename of the picture in the title bar. When you first created the form, you
changed its Text property in the Properties window. To create dynamic applications,
properties need to be constantly adjusted at runtime, and you do this using code.
Insert the following two statements, pressing Enter at the end of each line:
’ Show the name of the file in the form’s caption.
Me.Text = “Picture Viewer(“ & ofdselectpicture.FileName & “)”
After you’ve entered all the code, your editor should look like that shown in Figure 1.13.
Terminating a Program Using Code
The last bit of code you’ll write terminates the application when the user clicks the
Quit button. To do this, you need to access the Click event handler of the btnQuit
button. At the top of the code window are two tabs. The current tab says Viewer-
Form.vb*. This tab contains the code window for the form that has the filename ViewerForm.
vb. Next to this is a tab that says ViewerForm.vb [Design]*. Click this tab to
switch from Code view to the form designer. If you receive an error when you click the
FIGURE 1.13
Make sure that
your code exactly
matches the
code shown
here.
Running a Project 25
The Me.Close() statement closes the current form. When the last loaded form in
a program is closed, the application shuts itself down—completely. As you build
more robust applications, you’ll probably want to execute all kinds of cleanup routines
before terminating an application, but for this example, closing the form is
all you need to do.
By the
Way
Running a Project
Your application is now complete. Click the Save All button on the toolbar (the stack
of floppy disks), and then run your program by pressing F5. You can also run the program
by clicking the button on the toolbar that looks like a right-facing triangle and
resembles the Play button on a DVD player. (This button is called Start, and it can
also be found on the Debug menu.) Learning the keyboard shortcuts will make your
development process move along faster, so I recommend that you use them whenever
possible.
When you run the program, the Visual Basic interface changes, and the form you’ve
designed appears, floating over the design environment (see Figure 1.14).
You are now running your program as though it were a stand-alone application running
on another user’s machine; what you see is exactly what users would see if they
FIGURE 1.14
When in Run
mode, your program
executes
just as it would
for an end user.
tab, the code you entered contains an error, and you need to edit it to make it the
same as shown in Figure 1.13. After the form designer appears, double-click the Quit
button to access its Click event.
Enter the following code in the Quit button’s Click event handler; press Enter at the
end of each statement:
’ Close the window and exit the application
Me.Close()
26 HOUR 1: Jumping in with Both Feet: A Visual Basic 2010 Programming Tour
ran the program (without the Visual Studio 2010 design environment in the background,
of course). Click the Select Picture button to display the Select Picture dialog
box, shown in Figure 1.15. Use this dialog box to locate a picture file. When you’ve
found a file, double-click it, or click once to select it and then click Open. The selected
picture is then displayed in the picture box, as shown in Figure 1.16.
When you click the Select Picture button, the default path shown depends on
the last active path in Windows, so it might be different for you than shown in
Figure 1.15.
By the
Way
FIGURE 1.15
The
OpenFileDialog
control handles
all the details of
browsing for
files. Cool, huh?
FIGURE 1.16
What could be
prettier than a
1964 Fender
Super Reverb
amplifier?
Q&A 27
If you want to select and display a picture from your digital camera, chances are
the format is JPEG, so you’ll need to select this from the Files of Type drop-down.
Also, if your image is very large, you’ll see only the upper-left corner of the image
(what fits in the picture box). In later hours, I’ll show you how you can scale the
image to fit the picture box, and even resize the form to show a larger picture in
its entirety.
By the
Way
Summary
When you’re finished playing with the program, click the Quit button to return to
Design view.
That’s it! You’ve just created a bona fide Visual Basic program. You’ve used the toolbox
to build an interface with which users can interact with your program, and
you’ve written code in strategic event handlers to empower your program to do
things. These are the basics of application development in Visual Basic. Even the
most complicated programs are built using this fundamental approach: You build
the interface and add code to make the application do things. Of course, writing code
to do things exactly the way you want things done is where the process can get complicated,
but you’re on your way.
If you take a close look at the organization of the hours in this book, you’ll see that I
start out by teaching you the Visual Basic (Visual Studio .NET) environment. I then
move on to building an interface, and later I teach you about writing code. This
organization is deliberate. You might be eager to jump in and start writing serious
code, but writing code is only part of the equation—don’t forget the word Visual in
Visual Basic. As you progress through the hours, you’ll build a solid foundation of
development skills.
Soon, you’ll pay no attention to the man behind the curtain—you’ll be that man (or
woman)!
Q&A
Q. Can I show bitmaps of file types other than BMP and JPG?
A. Yes. PictureBox supports the display of images with the extensions BMP, JPG,
ICO, EMF, WMF, and GIF. PictureBox can even save images to a file using any
of the supported file types.
28 HOUR 1: Jumping in with Both Feet: A Visual Basic 2010 Programming Tour
Q. Is it possible to show pictures in other controls?
A. PictureBox is the control to use when you are just displaying images. However,
many other controls allow you to display pictures as part of the control.
For instance, you can display an image on a button control by setting the button’s
Image property to a valid picture.
Workshop
Quiz
1. What type of Visual Basic project creates a standard Windows program?
2. What window is used to change the attributes (location, size, and so on) of a
form or control in the IDE?
3. How do you access the default event (code) of a control?
4. What property of a picture box do you set to display an image?
5. What is the default event for a button control?
Answers
1. Windows Forms Application
2. The Properties window
3. Double-click the control in the designer
4. The Image property
5. The Click event
Exercises
1. Change your Picture Viewer program so that the user can also locate and select
GIF files. (Hint: Change the Filter property of the OpenFileDialog control.)
2. Create a new project with a new form. Create two buttons on the form, one above
the other. Next, change their position so that they appear next to each other.
29
HOUR 2
Navigating Visual Basic 2010
What You’ll Learn in This Hour:
. Navigating Visual Basic
. Using the Visual Studio 2010 Start Page to open and create projects
. Showing, hiding, docking, and floating design windows
. Customizing menus and toolbars
. Adding controls to a form using the toolbox
. Viewing and changing object attributes using the Properties window
. Working with the many files that make up a project
. How to get help
The key to expanding your knowledge of Visual Basic is to become as comfortable as
possible—as quickly as possible—with the Visual Basic design environment. Just as a
carpenter doesn’t think much about hammering a nail into a piece of wood, performing
actions such as saving projects, creating new forms, and setting object properties
should become second nature to you. The more comfortable you are with
Visual Basic’s tools, the more you can focus your energies on what you’re creating
with the tools.
In this hour, you’ll learn how to customize your design environment by moving,
docking, floating, hiding, and showing design windows, as well as how to customize
menus and toolbars. After you’ve gotten acquainted with the environment, I’ll teach
you about projects and the files they’re made of (taking you beyond what was briefly
discussed in Hour 1, “Jumping in with Both Feet: A Visual Basic 2010 Programming
Tour”). I’ll also introduce you to the design windows with which you’ll work most frequently.
Finally, I’ll show you how to get help when you’re stuck.
30 HOUR 2: Navigating Visual Basic 2010
Using the Visual Basic 2010 Start Page
By default, the Visual Basic 2010 Start Page, shown in Figure 2.1, is the first thing you
see when you start Visual Basic. (If Visual Basic isn’t running, start it now.) The Visual
Basic 2010 Start Page is a gateway for performing tasks with Visual Basic. From this
page, you can open previously edited projects, create new projects, and get help.
Creating New Projects
The Start Page consists of three category boxes. The Recent Projects category in the
upper-left corner is used to create new projects or open projects already created. To
create new projects, click the New Project link. This opens the New Project dialog box,
shown in Figure 2.2. The Templates list varies from machine to machine, depending
on which products of the Visual Studio .NET family are installed. Of course, we’re
interested in only the Visual Basic Project types in this book.
You can create many types of projects with Visual Basic. However, this book
focuses mostly on creating Windows Forms applications, the most common of the
project types and the primary application type of the Express edition of Visual
Basic 2010. You will learn about some of the other project types as well, but
when you’re told to create a new project and unless you are told otherwise, make
sure that the Windows Forms Application icon is selected.
By the
Way
FIGURE 2.1
The Start Page
is the default
entry point for all
.NET languages.
Using the Visual Basic 2010 Start Page 31
By the
Way
FIGURE 2.2
Use the New Project
dialog box to
create Visual
Basic projects
from scratch.
When you create a new project, be sure to enter a name for it in the Name text box
before clicking OK or double-clicking a Templates icon. This ensures that the project is
created with the proper path and filenames, eliminating work you would otherwise
have to do to change these values later. After you specify a name, you can create the
new project. Either double-click the type that represents the Template type of project
you want to create, or click the template icon to select it and then click OK. After
you’ve performed either of these actions, the New Project dialog box closes, and a
new project of the selected type is created.
When you first create a project, the project files are virtual—they haven’t been saved
to the hard drive. When you click Save or Save All for the first time, you are prompted
to specify a path in which to save the project. The name you give your project is used
as its folder name by default, but the path chosen depends on the last project you created.
If you’re on a team of developers, you might choose to locate your projects on a
shared drive so that others can access the source files.
You can create a new project at any time (not just when starting Visual Basic) by
choosing File, New Project. When you create or open a new project, the current
project is closed. Visual Basic asks whether you want to save any changes to the
current project before it closes it, however.
After you enter a project name and click OK, Visual Basic creates the project. Again,
nothing is saved to the hard drive until you click Save or Save All on the toolbar (or
use the menu equivalent).
32 HOUR 2: Navigating Visual Basic 2010
Opening an Existing Project
Over time, you’ll open existing projects more often than you create new ones. There
are essentially two ways to open projects from the Visual Studio Start Page:
. If it’s a project you’ve recently opened, the project name appears in the Recent
Projects category toward the upper-left corner of the Start Page (as Picture
Viewer does in Figure 2.1, shown earlier). Because the name displayed for the
project is the one given when it was created, it’s important to give your projects
descriptive names. Clicking a project name opens the project. I’d venture to
guess that you’ll use this technique 95% of the time.
. To open a project for the first time (such as when opening sample projects),
click the Open Project link on the Visual Basic 2010 Start Page. This displays a
standard dialog box that you can use to locate and select a project file.
As with creating new projects, you can open an existing project at any time, not
just when starting Visual Basic, by selecting File, Open Project. Remember that
opening a project causes the current project to be closed. Again, if you’ve made
changes to the current project, you’ll get a chance to save them before the project
is closed.
By the
Way
Navigating and Customizing the Visual
Basic Environment
Visual Basic lets you customize many of its interface elements such as windows and
toolbars, enabling you to be more efficient in the work you do. Create a new Windows
application now by opening the File menu and choosing New Project. This project
illustrates manipulating the design environment, so name this project
Environment Tutorial and click OK to create the project. (This exercise won’t create
anything reusable, but it will help you learn how to navigate the design environment.)
Your screen should look like the one shown in Figure 2.3.
Your screen might not look exactly like that shown in Figure 2.3, but it’ll be close.
By the time you’ve finished this hour, you’ll be able to change the appearance of
the design environment to match this figure—or to any configuration you prefer.
By the
Way
Working with Design Windows
Design windows, such as the Properties window and Solution Explorer shown in
Figure 2.3, provide functionality for building complex applications. Just as your desk
isn’t organized exactly like that of your coworkers, your design environment doesn’t
have to be the same as anyone else’s.
Navigating and Customizing the Visual Basic Environment 33
FIGURE 2.3
This is pretty
much how the
integrated development
environment
(IDE)
appears when
you first install
Visual Basic.
A design window can be placed in one of four primary states:
. Closed: The window is not visible.
. Floating: The window floats over the IDE.
. Docked: The window is attached to an edge of the IDE. The Solution Explorer
and Properties window in Figure 2.3 are docked.
. Automatically hidden: The window is docked, but it hides itself when not in
use (like the Toolbox).
Showing and Hiding Design Windows
When a design window is closed, it doesn’t appear anywhere. There is a difference
between being closed and being automatically hidden, as you’ll learn shortly. To display
a closed or hidden window, choose the corresponding menu item from the View
menu. For example, if the Properties window isn’t displayed in your design environment,
you can display it by choosing View, Other Windows, Properties Window (or by
pressing its keyboard shortcut—F4). Whenever you need a design window and can’t
find it, use the View menu to display it. To close a design window, click its Close button
(the button on the right side of the title bar with an X), just as you would close an
ordinary window.
34 HOUR 2: Navigating Visual Basic 2010
Floating Design Windows
Floating design windows are visible windows that float over the workspace, as shown
in Figure 2.4. Floating windows are like typical application windows in that you can
drag them around and place them anywhere you please, even on other monitors
when you’re using a multiple-display setup. In addition to moving a floating window,
you can change its size by dragging a border. To make a window float, click the title
bar of the docked window and drag it away from the edge that is currently docked.
Docking Design Windows
Visible windows appear docked by default. A docked window appears attached to the
side, top, or bottom of the work area or to some other window. The Properties window
shown in Figure 2.3, for example, is docked to the right side of the design environment
(contrast this to where it’s floating in Figure 2.4). To make a floating window
become a docked window, drag the title bar of the window toward the edge of the
design environment to which you want to dock the window. As you drag the window,
guides appear on the screen, as shown in Figure 2.5. If you move the mouse over one
of the icons that appear as part of the guides, Visual Basic shows a blue rectangle
where the window will appear if you release the mouse button. This is a quick and
easy way to dock a window. You can also drag the window to an edge and get the
same blue rectangle. This rectangle will “stick” in a docked position. If you release the
mouse while the rectangle appears this way, the window is docked. Although it’s difficult
to explain, this is very easy to do.
FIGURE 2.4
Floating windows
appear over the
top of the design
environment.
Navigating and Customizing the Visual Basic Environment 35
FIGURE 2.5
The guide icons
make it easy to
dock a window.
You can size a docked window by dragging its edge opposite the side that’s
docked. If two windows are docked to the same edge, dragging the border
between them enlarges one while shrinking the other.
By the
Way
To try this, you’ll need to float a window that’s already docked. To float a window,
you “tear” the window away from the docked edge by dragging the title bar of the
docked window away from the edge to which it’s docked. Note that this technique
doesn’t work if a window is set to Auto Hide (which is explained next). Try docking
and floating windows now by following these steps:
1. Ensure that the Properties window is currently displayed (if it’s not, show it by
pressing F4). Make sure that the Properties window isn’t set to Auto Hide by
right-clicking its title bar and deselecting Auto Hide from the shortcut menu (if
it’s selected).
2. Drag the title bar of the Properties window away from the docked edge (drag it
to the left). When the window is away from the docked edge, release the mouse
button. The Properties window should now float.
36 HOUR 2: Navigating Visual Basic 2010
3. Dock the window once more by dragging the window’s title bar toward the
right edge of the design environment. When the guide diamond appears,
mouse over the bottom icon (see Figure 2.5). You see a blue rectangle appear
where the Properties window will be docked. Release the mouse button to dock
the window.
If you don’t want a floating window to dock, regardless of where you drag it, rightclick
the window’s title bar and choose Floating from the context menu. To allow
the window to be docked again, right-click the title bar and choose Dockable.
Did you
Know?
Auto-Hiding Design Windows
Visual Basic windows can auto hide themselves when you’re not using them.
Although you might find this a bit disconcerting at first, after you get the hang of
things, this is a productive way to work. Your workspace is freed up, yet design windows
are available whenever you move the mouse over them. Windows that are set
to Auto Hide are always docked; you can’t set a floating window to Auto Hide. When
a window auto hides, it appears as a vertical tab on the edge to which it’s docked—
much as minimized applications are placed in the Windows taskbar.
Look at the left edge of the design environment. Notice the vertical tab titled Toolbox.
This tab represents an auto-hidden window. To display an auto-hidden window, move
the pointer over the tab representing the window. When you move the pointer over a
tab, Visual Basic displays the design window so that you can use its features. When
you move the pointer away from the window, the window automatically hides itself—
hence the name. To make any window hide itself automatically, right-click its title
bar and select Auto Hide from its shortcut menu. You can also click the little picture
of a pushpin appearing in the title bar next to the Close button to toggle the window’s
Auto Hide state.
Using the techniques discussed so far, you can tailor the appearance of your design
environment in all sorts of ways. There is no one best configuration. You’ll find that
different configurations work better for different projects and in different stages of
development. Sometimes when I’m designing the interface of a form, for example, I
want the toolbox to stay visible but out of my way, so I tend to make it float, or I turn
off its Auto Hide property and leave it docked to the left edge of the design environment.
However, after the majority of the interface elements have been added to a
form, I want to focus on code. Then I dock the toolbox and make it auto-hide itself;
it’s there when I need it, but it’s out of the way when I don’t. Don’t be afraid to experiment
with your design windows, and don’t hesitate to modify them to suit your
changing needs.
Working with Toolbars 37
Working with Toolbars
Toolbars are the mainstay for performing functions quickly in almost every Windows
program. (You’ll probably want to add them to your own programs at some point,
and in Hour 9, “Adding Menus and Toolbars to Forms,” I’ll show you how.) Every
toolbar has a corresponding menu item, and buttons on toolbars are essentially
shortcuts to their corresponding menu items. To maximize your efficiency when
developing with Visual Basic 2010, you should become familiar with the available
toolbars. As your skills improve, you can customize existing toolbars and even create
your own toolbars to more closely fit the way you work.
Showing and Hiding Toolbars
Visual Basic includes a number of built-in toolbars you can use when creating projects.
One toolbar is visible in most of the figures shown so far in this hour: the Standard
toolbar. You’ll probably want this toolbar displayed all the time.
The toolbars you’ll use most often as a new Visual Basic developer are the Standard,
Text Editor, and Debug toolbars; each of these is discussed in this hour. You can also
create your own custom toolbars to contain any functions you think necessary.
To show or hide a toolbar, open the View menu and choose Toolbars to display a list
of available toolbars. Toolbars that are currently visible are checked, as shown in
Figure 2.6. Click a toolbar name to toggle its visible state.
FIGURE 2.6
Hide or show
toolbars to make
your workspace
more efficient.
38 HOUR 2: Navigating Visual Basic 2010
You can also right-click any visible toolbar to quickly access the list of available
toolbars.
Did you
Know?
Docking and Resizing Toolbars
Just as you can dock and undock Visual Basic’s design windows, you can dock and
undock the toolbars. Unlike the design windows, however, Visual Basic’s toolbars
don’t have a title bar that you can click and drag when they’re in a docked state.
Instead, each docked toolbar has a drag handle (a vertical stack of dots along its left
edge). To float (undock) a toolbar, click and drag the grab handle away from the
docked edge. When a toolbar is floating, it has a title bar, which you can drag to an
edge to dock the toolbar. This is the same technique you use to dock design windows.
A shortcut for docking a floating toolbar, or any other floating window, is to doubleclick
its title bar.
Did you
Know?
Although you can’t change the size of a docked toolbar, you can resize a floating
toolbar (a floating toolbar behaves like any other normal window). To resize a floating
toolbar, move the pointer over the edge you want to stretch, and then click and
drag to the border to change the toolbar’s size.
Adding Controls to a Form Using the
Toolbox
The IDE offers some fantastic tools for building a graphical user interface (GUI) for
your applications. Most GUIs consist of one or more forms (Windows) with various elements
on the forms, such as text boxes, list boxes, and buttons. The toolbox is used to
place controls on a form. Figure 2.7 shows the default toolbox you see when you first
open or create a Visual Basic project. These controls are discussed in detail in Hour 7,
“Working with Traditional Controls,” and Hour 8, “Using Advanced Controls.”
You can add a control to a form in one of four ways:
. In the toolbox, click the tool representing the control that you want to place on
a form, and then click and drag on the form where you want the control
placed. You’re essentially drawing the border of the control. The location at
which you start dragging is used for one corner of the control, and the point at
which you release the mouse button and stop dragging becomes the lower-right
corner.
Adding Controls to a Form Using the Toolbox 39
FIGURE 2.7
The standard
toolbox contains
many useful controls
you can use
to build robust
interfaces.
. Double-click the desired control type in the toolbox. A new control of the
selected type is placed in the upper-left corner of the form if the form is selected.
If a control is selected when you do this, the new control appears slightly to the
right and down from the selected control. The control’s height and width are set
to the default height and width of the selected control type. If the control is a
runtime-only control, such as the OpenFileDialog control you used in Hour 1,
it appears below the form.
. Drag a control from the toolbox and drop it on a form. If you hover the mouse
pointer over the form for a second, the toolbox disappears, and you can drop
the control on the form anywhere you want.
. Right-click an existing control and choose Copy; then right-click the form and
choose Paste to create a duplicate of the control.
If you prefer to draw controls on your forms by clicking and dragging, I strongly
suggest that you dock the toolbox to the right or bottom edge of the design environment
or float it. The toolbar tends to interfere with drawing controls when it’s
docked to the left edge because it covers part of the form.
Did you
Know?
The first item in each category in the toolbox, titled Pointer, isn’t actually a control.
When the pointer item is selected, the design environment is placed in a select mode
rather than in a mode to create a new control. With the pointer item selected, you
can click a control on the form to display all its properties in the Properties window.
40 HOUR 2: Navigating Visual Basic 2010
Setting Object Properties Using the
Properties Window
When developing a project’s interface, you’ll spend a lot of time viewing and setting
object properties in the Properties window, shown in Figure 2.8. The Properties window
contains four items:
. An object drop-down list
. A list of properties
. A set of tool buttons used to change the appearance of the properties grid
. A section showing a description of the selected property
Selecting an Object and Viewing Its Properties
The drop-down list at the top of the Properties window contains the name of the form
with which you’re currently working and all the objects on the form (the form’s controls).
To view a control’s properties, select it from the drop-down list, or find it on the
form and click it. Remember that you must have the pointer item selected in the toolbox
to click an object to select it.
Viewing and Changing Properties
The first two buttons in the Properties window (Categorized and Alphabetic) enable
you to select the format in which you view properties. When you select the Alphabetic
FIGURE 2.8
Use the Properties
window to
view and change
properties of
forms and controls.
Setting Object Properties Using the Properties Window 41
button, the selected object’s properties appear in the Properties window in alphabetical
order. When you click the Categorized button, all the selected object’s properties
are listed by category. The Appearance category, for example, contains properties
such as BackColor and BorderStyle. When working with properties, select the view
with which you’re most comfortable and feel free to switch back and forth between
the views.
The Properties pane of the Properties window is used to view and set the properties of
a selected object. You can set a property in one of the following ways:
. Type in a value.
. Select a value from a drop-down list.
. Click a Build button for property-specific options.
You can use more than one of these methods to change many properties. For
example, color properties supply a drop-down list of colors, but you can enter a
numeric color value as well.
By the
Way
To better understand how changing properties works, follow these steps:
1. Add a new text box to the form by double-clicking the TextBox tool in the toolbox.
Next you’ll change a few properties of the new text box.
2. Select the Name property in the Properties window by clicking it. (If your properties
are alphabetic, it will be at the top of the list, not with the N’s.) Type in a
name for the text box—call it txtComments.
3. Click the BorderStyle property and try to type in the word Big. You can’t; the
BorderStyle property supports only the selection of values from a list,
although you can type a value that exists in the list. When you select the
BorderStyle property, a drop-down arrow appears in the Value column. Click
this arrow to display a list of the values that the BorderStyle property accepts.
Select FixedSingle and notice how the appearance of the text box changes. To
make the text box appear three-dimensional again, open the drop-down list
and select Fixed3D.
If you are running your display using Windows 7, Vista, or the Windows XP Theme
on XP, controls don’t take on a 3D appearance—they appear flat with a light blue
border. I’m a big fan of this newer interface, and all the figures in this book were
captured running on Windows 7.
By the
Way
4. Select the BackColor property, type the word guitar, and press the Tab key to
commit your entry. Visual Basic displays a message telling you the property
42 HOUR 2: Navigating Visual Basic 2010
value isn’t valid. This happens because although you can type in text, you’re
restricted to entering specific values. In the case of BackColor, the value must
be a named color or a number that falls within a specific range. Clear out the
text, click the drop-down arrow of the BackColor property, and select a color
from the drop-down list.
5. Select the Font property. Notice that a Build button appears (a small button
with three dots). When you click the Build button, a dialog box specific to the
property you’ve selected appears. In this instance, a dialog box that lets you
manipulate the font of the text box appears, as shown in Figure 2.9. Different
properties display different dialog boxes when you click their Build buttons.
Feel free to change the font, and then close the window.
6. Scroll down to the Size property and notice that it has a right-facing triangle
next to it. This indicates that the property has one or more subproperties. Click
the triangle to expand the property, and you’ll see that Size is composed of
Width and Height.
By simply clicking a property in the Properties window, you can easily tell the type of
input the property requires.
Working with Color Properties
Properties that deal with colors are unique in how they accept values, yet all colorrelated
properties behave the same way. In Visual Basic, colors are expressed as a set
of three numbers, each having a value from 0 to 255. A given set of numbers represents
the red, green, and blue (RGB) components of a color, respectively. The value
0,255,0, for example, represents pure green, whereas the value 0,0,0 represents black
FIGURE 2.9
The Font dialog
box allows you
to change the
appearance of
text in a control.
Setting Object Properties Using the Properties Window 43
and 255,255,255 represents white. In some cases, colors have also been given specific
names that you can use.
A color rectangle is displayed for each color property in the Properties window; this
color is the selected color for the property. Text is displayed next to the colored rectangle.
This text is either the name of a color or a set of RGB values that define the color.
Clicking a color property causes a drop-down arrow to appear, but the drop-down you
get by clicking the arrow isn’t a typical drop-down list. Figure 2.10 shows what the
drop-down list for a color property looks like when the System tab is selected.
The color drop-down list is composed of three tabs: Custom, Web, and System. Most
color properties use a system color by default. Hour 5, “Building Forms: The Basics,”
goes into great detail on system colors. I only want to mention here that system colors
vary from computer to computer. They’re determined by the users when they rightclick
the desktop and choose to personalize their colors. Use a system color when you
want a color to be one of the user’s selected system colors. When a color property is
set to a system color, the name of the system color appears in the property sheet.
The Custom tab, shown in Figure 2.11, is used to specify a color regardless of the
user’s system color settings; changes to system colors have no effect on the property.
The most common colors appear on the palette of the Custom tab, but you can specify
any color you want.
FIGURE 2.10
The color dropdown
list
enables you to
select from three
sets of colors:
Custom, Web,
and System.
FIGURE 2.11
The Custom tab
of the color dropdown
list lets
you specify any
color
imaginable.
44 HOUR 2: Navigating Visual Basic 2010
The colors visible in the various palettes are limited by the number of colors that
your video card can produce. If your video card doesn’t support enough colors,
some will appear dithered, which means that they will appear as dots of colors
rather than as a true, solid color. Keep this in mind as you develop your applications:
What looks good on your computer might turn to mush if a user’s display
isn’t as capable.
By the
Way
The bottom two rows in the Custom color palette are used to mix your own colors. To
assign a color to an empty color slot, right-click a slot in one of the two rows to access
the Define Color dialog box, shown in Figure 2.12. Use the controls in the Define
Color dialog box to create the color you want, and then click Add Color to add the
color to the color palette in the slot you selected. In addition, the custom color is automatically
assigned to the current property.
The Web tab is used in web applications to pick from a list of browser-safe colors.
However, you can use these colors even if you’re not creating a web application.
Viewing Property Descriptions
It’s not always immediately apparent just exactly what a property is or does—especially
for new users of Visual Basic. The Description section at the bottom of the Properties
window shows a simple description of the selected property. To view a description,
click a property or value area of a property. For a more complete description of a property,
click it to select it and then press F1 to display Help about the property.
You can hide or show the Description section of the Properties window at any time.
Right-click anywhere within the Properties window (other than in the value column
or on the title bar) to display the Properties window shortcut menu and then choose
FIGURE 2.12
The Define Color
dialog box
enables you to
create your own
colors.
Managing Projects 45
Description. Each time you do this, you toggle the Description section between visible
and hidden. To change the size of the Description box, click and drag the border
between it and the Properties pane.
Managing Projects
Before you can effectively create an interface and write code, you need to understand
what makes up a Visual Basic 2010 project and how to add and remove various components
within your own projects. In this section, you’ll learn about the Solution
Explorer window and how it’s used to manage project files. You’ll also learn specifics
about projects and project files, including how to change a project’s properties.
Managing Project Files with the Solution Explorer
As you develop projects, they’ll become more and more complex, often containing
many objects such as forms and modules (grouped sets of code). Each object is
defined by one or more files on your hard drive. In addition, you can build complex
solutions composed of more than one project. The Solution Explorer window, shown
in Figure 2.13, is the tool for managing all the files in a simple or complex solution.
Using the Solution Explorer, you can add, rename, and remove project files, as well as
select objects to view their properties. If the Solution Explorer window isn’t visible on
your screen, show it now by choosing View, Other Windows, Solution Explorer.
To better understand the Solution Explorer window, follow these steps:
1. Locate the Picture Viewer program you created in Hour 1 by choosing File,
Open Project. If prompted, do not save your current project.
2. Open the Picture Viewer project. The file you need to select is located in the Picture
Viewer folder that Visual Basic created when the project was constructed.
The file has the extension .vbproj (for Visual Basic Project). If you’re asked
whether you want to save the current project, choose No.
FIGURE 2.13
Use the Solution
Explorer window
to manage all
the files that
make up a
project.
46 HOUR 2: Navigating Visual Basic 2010
3. Select the Picture Viewer project item in the Solution Explorer. When you do, a
button becomes visible toward the top of the window. This button has a picture
of pieces of paper and has the ToolTip Show All Files, as shown in Figure 2.14.
Click this button, and the Solution Explorer displays all files in the project.
Some forms and other objects might be composed of more than one file. By
default, Visual Basic hides project files that you don’t directly manipulate. Click
the right-facing triangle next to the ViewerForm.vb form item, and you’ll see
subitems titled ViewerForm.resx and ViewerForm.Designer.vb. You’ll learn
about these additional files in Hour 5. For now, click the Show All Files button
again to hide these related files.
By the
Way
You can view any object listed within the Solution Explorer with the object’s default
viewer by double-clicking the object. Each object has a default viewer but might actually
have more than one viewer. For instance, a form has a Form Design view as well
as a Code view. By default, double-clicking a form in the Solution Explorer displays
the form in Form Design view, where you can manipulate the form’s interface.
You’ve already learned one way to access the code behind a form: Double-click an
object to access its default event handler. You’ll frequently need to get to a form’s code
without adding a new event handler. One way to do this is to use the Solution
Explorer. When a form is selected in the Solution Explorer, buttons are visible at the
top of the Solution Explorer window that can be used to display the code editor or the
form designer.
You’ll use the Solution Explorer window so often that you’ll probably want to dock it
to an edge and set it to Auto Hide, or perhaps keep it visible all the time. The Solution
Explorer window is one of the easiest to get the hang of in Visual Basic. Navigating
the Solution Explorer window will be second nature to you before you know it.
Working with Solutions
A project is what you create with Visual Basic. Often, the words project and program
are used interchangeably, but this isn’t much of a problem if you understand the
FIGURE 2.14
Click Show All
Files to view secondary
file information.
Managing Projects 47
important distinctions. A project is the set of source files that make up a program or
component. A program is the binary file that you build by compiling source files into
something such as a Windows executable file (.exe). Projects always consist of a
main project file and can be made up of any number of other files, such as form files or
class module files. The main project file stores information about the project—all the
files that make up the project, for example—as well as properties that define aspects of
a project, such as the parameters to use when the project is compiled into a program.
What, then, is a solution? As your abilities grow and your applications increase in
complexity, you’ll find that you have to build multiple projects that work harmoniously
to accomplish your goals. For instance, you might build a custom user control
such as a custom data grid that you use within other projects you design. Or you
might isolate the business rules of a complex application into separate components
to run on isolated servers. All the projects used to accomplish those goals are collectively
called a solution. Therefore, a solution (at its most basic level) is really nothing
more than a grouping of projects.
You should group projects into a single solution only when the projects relate to
one another. If you’re working on a number of projects, but each of them is
autonomous, work with each project in a separate solution.
Did you
Know?
Visual Basic creates a solution file for you when you save a project. The solution file is
saved with the extension .sln, and you can open this file just as you would a project
file. If a solution contains a single project, it really doesn’t matter which you open—
the solution or the project file. However, when you need to work with multiple projects
together, you should open the solution file.
Understanding Project Components
As I stated earlier, a project always consists of a main project file, and it might consist
of one or more secondary files, such as files that make up forms or code modules. As
you create and save objects within your project, one or more corresponding files are
created and saved on your hard drive. Each file that’s created for a Visual Basic 2010
source object has the extension .vb, denoting that it defines a Visual Basic object. Be
sure that you save your objects with understandable names, or things will get confusing
as your project grows in size.
With previous editions of Visual Basic (version 6 and earlier), you could easily tell
the type of object defined by project files by looking at the file extension. For
example, form files had the extension .frm. Unfortunately, this is no longer the
case, so you need to be diligent about giving your files unique names.
By the
Way
48 HOUR 2: Navigating Visual Basic 2010
All files that make up a project are text files. Some objects need to store binary information,
such as a picture for a form’s BackgroundImage property. Binary data is
stored in an XML file (which is still a text file). Suppose that you had a form with an
icon on it. You’d have a text file defining the form—its size, the controls on it, and the
code behind it. You also would have an associated resource file with the same name
as the form file, but with the extension .resx. This secondary file would be in XML
format and would contain all the binary data needed to create the form.
If you want to see what the source file of a form file looks like, use Notepad to
open one on your computer. Don’t save any changes to the file, however, or it
might never work again (insert evil laugh here).
By the
Way
The following is a list of some of the components you might use in your projects:
. Modules enable you to store code procedures without needing a specific form to
attach them to.
. A class modules is a special type of module that enables you to create objectoriented
applications. Throughout the course of this book, you’ll learn how to
program using an object-oriented language, but mostly you’ll learn how to use
objects supplied by Visual Basic. In Hour 16, “Designing Objects Using Classes,”
you’ll learn how to use class modules to create your own objects.
. Forms are the visual windows that make up your application’s interface. A special
type of class module is used to define forms.
. User controls (formerly ActiveX controls, which themselves are formerly OLE
controls) are controls that can be used on the forms of other projects. For example,
you could create a user control with a calendar interface for a contact manager.
Creating user controls requires much programming experience, so I won’t
cover them in this book.
Setting Project Properties
Visual Basic projects have properties, just as other objects such as controls do. Projects
have many properties, many of them related to advanced functionality not covered
in this book. You need to be aware of how to access project properties, however, and
how to change some of the more commonly used properties.
To access the properties for a project, right-click the project name (Picture Viewer) in
the Solution Explorer window and choose Properties from the shortcut menu. You
Managing Projects 49
could also double-click the My Project item in the Solutions Explorer to accomplish
the same goal. Perform one of these actions now.
The properties for a project are presented as a set of vertical tabs, as shown in
Figure 2.15.
As you work through the hours in this book, I’ll refer to the Project Properties dialog
box as necessary, explaining pages and items in context with other material. Feel free
to take a look at your Picture Viewer properties, but don’t change any at this time.
You can close the project properties by clicking the small X in the upper-right corner
of the tab section in the IDE. You can also just click a different tab.
Adding and Removing Project Files
When you first start Visual Basic 2010 and create a new Windows Forms Application
project, Visual Basic creates the project with a single form. You’re not limited to having
one form in a project, however; you can create new forms or add existing forms to
your project at will (feeling powerful yet?). You can also create and add code modules
and classes as well as other types of objects.
You can add a new or existing object to your project in one of three ways:
. Choose the appropriate item from the Project menu.
. Click the small drop-down arrow that’s part of the Add New Item button on the
Standard toolbar, and then choose from the menu that appears (see Figure 2.16).
FIGURE 2.15
The project properties
are used
to tailor the project
as a whole.
50 HOUR 2: Navigating Visual Basic 2010
. Right-click the project name in the Solution Explorer window, and then choose
Add from the shortcut menu to access a submenu from which you can select
object types.
When you select Add ObjectType from any of these menus, a dialog box appears,
showing you the objects that can be added to the project. Your chosen item type is
selected by default, as shown in Figure 2.17. Simply name the object and click Open
to create a new object of the selected type. To create an object of a different type, click
the type to select it, name it, and then click Open.
Adding new forms and modules to your project is easy, and you can add as many as
you want. You’ll come to rely on the Solution Explorer more and more to manage all
the objects in the project as the project becomes more complex.
Although it won’t happen as often as adding project files, you might sometimes need
to remove an object from a project. Removing objects from your project is even easier
than adding them. To remove an object, right-click the object in the Solution Explorer
window and select Delete. This not only removes the object from the project, it also
deletes the source file from the disk!
FIGURE 2.16
This toolbutton
drop-down is one
of three ways to
add objects to a
project.
FIGURE 2.17
Regardless of
the menu option
you select, you
can add any type
of object you
want by using
this dialog box.
A Quick-and-Dirty Programming Primer 51
A Quick-and-Dirty Programming Primer
Programming is complicated. Everything is so interrelated that it’s difficult, if not
impossible, to isolate each programming concept and then present the material in a
linear fashion. Instead, while learning one subject, you often have to touch on elements
of another subject before you’ve had a chance to learn about the secondary
topic. As I mentioned in Hour 1, I’ve made every effort to avoid such forward references,
but there are some concepts you’ll need to be at least slightly familiar with
before proceeding. You’ll learn the basics of each of these topics in their respective
hours, but you’ll need to have at least heard of them before digging any deeper into
this book.
Storing Values in Variables
A variable is an element in code that holds a value. You might create a variable that
holds the name of a user or perhaps the user’s age, for example. Each variable (storage
entity) must be created before it can be used. The process of creating a variable is
known as declaring a variable. In addition, each variable is declared to hold data of a
specific type, such as text (called a string) for a person’s name or a number for a person’s
age. An example of a variable declaration is
Dim strFirstName As String
This statement creates a variable called strFirstName. This variable is of type
String, which means that it can hold any text you choose to put into it. The contents
of a variable can be changed as often as you like.
The key primer point to remember is that variables are storage locations that must be
declared before use and that hold a specific type of data.
Using Procedures to Write Functional Units of Code
When you write Visual Basic code, you place the code in a procedure. A procedure is a
group of code statements that perform a specific function. You can call a procedure
from code in another procedure. For example, you might create one procedure that
totals the items on an order and another procedure that calculates the tax on the
entire sale. There are two types of procedures: procedures that don’t return values and
procedures that do return values. In addition, some procedures allow data to be
passed to them. For example, the tax calculation procedure mentioned previously
might allow a calling statement to pass a monetary total into the procedure and then
use that total to calculate tax. When a procedure accepts data from the calling code,
the data is called a parameter. Procedures don’t have to accept parameters.
52 HOUR 2: Navigating Visual Basic 2010
The keyword Sub is used to declare a procedure that doesn’t return a value. It looks like
this:
Public Sub MyProcedure()
‘ The procedure’s code goes here.
End Sub
The keyword Function is used to delare a procedure that returns a value. In addition,
it has a data type specified at the end of the procedure, which denotes the type of
data returned by the procedure:
Public Function MyProcedure() As String
‘ The procedure’s code goes here.
End Function
Notice the words As String. The keyword As is used to specify a data type. In this
example, the function returns a string, which is text.
If a procedure accepts a parameter, it is enclosed in the parentheses. Again, notice
how the word As is used to denote the type of data being accepted:
Public Function CalculateTax(dblItemTotal As Double) As String
‘ The procedure’s code goes here.
End Function
MessageBox.Show()
You’re almost certainly familiar with the Windows message box. It’s the little dialog
box used to display text to a user, as shown in Figure 2.18. Visual Basic 2010 provides
an easy way to display such messages: the MessageBox.Show() statement. The following
is a MessageBox.Show() statement in its most basic form:
MessageBox.Show(“This is a standard message box”)
You’ll use message boxes throughout this book, and you’ll learn about them in detail
in Hour 17, “Interacting with Users.”
FIGURE 2.18
Visual Basic
makes it easy to
display simple
message boxes
like this.
Summary 53
Getting Help
Although Visual Basic was designed to be as intuitive as possible, you’ll find that you
occasionally need help performing a task. In all honesty, Visual Basic isn’t as intuitive
as its predecessors. With all its additional power and flexibility comes complexity.
It doesn’t matter how much you know; Visual Basic is so complex and contains so
many features that you’ll have to use Help at times. This is particularly true when
writing Visual Basic code; you won’t always remember the command you need or a
command’s syntax. Fortunately, Visual Basic includes a comprehensive Help feature.
Unfortunately, it isn’t as complete as it could be.
To access Help from within the design environment, press F1. Generally, when you
press F1, Visual Basic shows you a Help topic directly related to what you’re doing.
This is known as context-sensitive help, and when it works, it works well. For example,
you can display help for any Visual Basic syntax or keyword (functions, objects, methods,
properties, and so on) when writing Visual Basic code. Type the word into the
code editor, position the cursor anywhere within the word (including before the first
letter or after the last), and press F1. You can also get to Help by using the Help menu.
If your project is in Run mode, Visual Basic’s Help doesn’t appear when you press
F1. Instead, the Help for your application appears—if you’ve created Help.
By the
Way
Summary
In this hour, you learned how to use the Visual Basic Start Page—your gateway to
Visual Basic 2010. You learned how to create new projects and how to open existing
projects. The Visual Basic environment is your workspace, toolbox, and much more.
You learned how to navigate this environment, including how to work with design
windows (hide, show, dock, and float).
Visual Basic has many different design windows, and in this hour, you began learning
about some of them in detail. You learned how to get and set properties using the
Properties window, how to manage projects using the Solution Explorer, and how to
add controls to a form using the toolbox. You’ll use these skills often, so it’s important
to get familiar with them right away. Finally, you learned how to access Visual Basic’s
Help feature, which I guarantee you’ll find important as you learn to use Visual Basic.
Visual Basic 2010 is a vast and powerful development tool—far more powerful than
any version that’s come before it. Don’t expect to become an expert overnight; that’s
simply not possible. However, by learning the tools and techniques presented in this
hour, you’ve begun your journey. Remember, you’ll use most of what you learned in
this hour each time you use Visual Basic. Get proficient with these basics, and you’ll
be building useful programs in no time!
54 HOUR 2: Navigating Visual Basic 2010
Q&A
Q. How can I easily get more information about a property when the Description
section of the Properties window just doesn’t cut it?
A. Click the property in question to select it, and then press F1. Context-sensitive
Help applies to properties in the Properties window as well.
Q. I find that I need to see a lot of design windows at one time, but I can’t find
that “magic” layout. Any suggestions?
A. Run at a higher resolution. Personally, I won’t develop in less than 1024×768.
As a matter of fact, all my development machines have two displays, both running
at 1680×1050 or higher. You’ll find that any investment you make in having
more screen real estate will pay big dividends.
Workshop
Quiz
1. Unless instructed otherwise, you’re to create what type of project when building
examples in this book?
2. To make a docked design window appear when you hover the mouse pointer
over its tab and disappear when you move the mouse away from it, you
change what setting of the window?
3. What design window do you use to add controls to a form?
4. What design window is used to change an object’s attributes?
5. To modify a project’s properties, you must select the project in what design
window?
Answers
1. Windows Forms Application
2. Its Auto Hide settings
3. The toolbox window
4. The Properties window
5. The Solutions Explorer window
Workshop 55
Exercises
1. Use the Custom Color dialog box to create a color of your choice, and then
assign the color to the BackColor property of a form.
2. Move the toolbox to the right side of the IDE and dock it there. Make it Auto
Hide. When you’re finished, move it back.
This page intentionally left blank
57
HOUR 3
Understanding Objects and
Collections
What You’ll Learn in This Hour:
. Understanding objects
. Getting and setting properties
. Triggering methods
. Understanding method dynamism
. Writing object-based code
. Understanding collections
. Using the Object Browser
In Hour 1, “Jumping in with Both Feet: A Visual Basic 2010 Programming Tour,” you
were introduced to programming in Visual Basic by building a Picture Viewer project.
You then spent Hour 2, “Navigating Visual Basic 2010,” digging into the integrated
development environment (IDE) and learning skills critical to your success with
Visual Basic. In this hour, you begin learning about an important programming concept:
objects.
The term object as it relates to programming might have been new to you prior to
this book. The more you work with Visual Basic, the more you’ll hear about objects.
Visual Basic 2010, unlike its early predecessors, is a true object-oriented language.
This hour doesn’t discuss object-oriented programming in any detail; object-oriented
programming is a complex subject and well beyond the scope of this book. Instead,
you’ll learn about objects in a more general sense.
Everything you use in Visual Basic is an object, so understanding this material is critical
to your success with Visual Basic. For example, forms are objects, as are the controls
you place on a form. Pretty much every element of a Visual Basic project is an
object and belongs to a collection of objects. All objects have attributes (called
58 HOUR 3: Understanding Objects and Collections
properties), most have methods, and many have events. Whether creating simple
applications or building large-scale enterprise solutions, you must understand what
an object is and how it works. In this hour, you’ll learn what makes an object an
object, and you’ll also learn about collections.
If you’ve listened to the programming press at all, you’ve probably heard the term
object-oriented, and perhaps words such as polymorphism, encapsulation, and
inheritance. In truth, these object-oriented features of Visual Basic are exciting,
but they’re far beyond this hour (or the last hour, for that matter). You’ll learn a little
about object-oriented programming in this book, but if you’re really interested
in taking your programming skills to the next level, you should buy a book dedicated
to the subject after you’ve completed this book.
By the
Way
Understanding Objects
Object-oriented programming has been a technical buzzword for quite some time, but
as far as Visual Basic programmers are concerned, it became a reality only with
Visual Basic .NET. (No previous version of Visual Basic was a true object-oriented language.)
Almost everywhere you look—the Web, publications, books—you read about
objects. What exactly is an object? Strictly speaking, an object is a programming
structure that encapsulates data and functionality as a single unit and for which the
only public access is through the programming structure’s interfaces (properties,
methods, and events). In reality, the answer to this question can be somewhat
ambiguous, because there are so many types of objects—and the number grows
almost daily. All objects share specific characteristics, however, such as properties and
methods.
The most commonly used objects in Visual Basic are the form object and the control
object. Earlier hours introduced you to working with forms and controls and even
showed you how to set form and control properties. In your Picture Viewer project
from Hour 1, for example, you added a picture box and two buttons to a form. Both
the PictureBox and the Button controls are control objects, but each is a specific type
of control object. Another, less-technical example uses pets. Dogs and cats are definitely
different entities (objects), but they both fit into the category of pet objects. Similarly,
a text box and a button is each a unique type of object, but they’re both
considered control objects. This small distinction is important.
Understanding Properties
All objects have attributes that are used to specify and return the state of the object.
These attributes are properties, and you’ve already used some of them in previous
hours in the Properties window. Indeed, every object exposes a specific set of proper-
Understanding Properties 59
ties, but not every object exposes the same set of properties. To illustrate this point, I’ll
continue with the hypothetical pet object. Suppose that you have an object, and the
object is a dog. This Dog object has certain properties common to all dogs. These
properties include attributes such as the dog’s name, the color of its hair, and even
the number of legs it has. All dogs have these same properties; however, different
dogs have different values for these properties. Figure 3.1 illustrates such a Dog object
and its properties.
Getting and Setting Properties
You’ve already seen how to read and change properties using the Properties window.
The Properties window is available only at design time, however, and is used only to
manipulate the properties of forms and controls. Most getting and setting of properties
you’ll perform will be done with Visual Basic code, not in the Properties window.
When referencing properties in code, you specify the object’s name first, followed by a
period (.), and then the property name, as in the following syntax:
ObjectName.Property
If you had a Button object named btnClickMe, for example, you would reference the
button’s Text property this way:
btnClickMe.Text
This line of code would return whatever value was contained in the Text property of
the Button object btnClickMe. To set a property to some value, you use an equals
sign (=). To change the Button object’s Left property, for example, you’d use a line of
code such as the following:
btnClickMe.Left = 90
Dog Object
Properties
Name
Sex
Weight
HairColor
NumberofLegs
FIGURE 3.1
Properties are
the attributes
that describe an
object.
60 HOUR 3: Understanding Objects and Collections
When you reference a property on the left side of an equals sign, you’re setting the
value. When you reference a property on the right side of the equals sign, you’re getting
(reading) the value. In the early days of BASIC, you actually used the word Let
when setting values. This made the code easier to read for novices, but it was unnecessarily
tedious. Nevertheless, using Let makes the statement clearer for this example,
so I’ll show the same code statement as before with the word Let:
Let btnClickMe.Left = 90
It’s easier to see here that referencing the property on the left side of the equals sign
indicates that you’re setting the property to some value. The keyword Let is no longer
a valid way to make variable assignments. If you enter a code statement that uses
Let, you won’t receive an error, but the code editor (also known as the gremlins) automatically
removes the word Let from the statement for you.
The following line of code places the value of the Left property of the Button object
called btnClickMe into a temporary variable. This statement retrieves the value of
the Left property because the Left property is referenced on the right side of the
equals sign.
intLeftVariable = btnClickMe.Left
Variables are discussed in detail in Hour 11, “Using Constants, Data Types, Variables,
and Arrays.” For now, think of a variable as a storage location. When the processor
executes this statement, it retrieves the value in the Left property of the Button
object btnClickMe and places it in the variable (storage location) titled
intLeftVariable. Assuming that btnClickMe’s Left property value is 90, as set in
the previous example, the computer would process the code statement like this:
intLeftVariable = 90
Just as in real life, some properties can be read but not changed. Think back to the
hypothetical pet object, and suppose that you have a Gender property to designate
the gender of a Dog object. It’s impossible for you to change a dog from a male to a
female or vice versa (at least, I think it is). Because the Gender property can be
retrieved but not changed, it’s known as a read-only property. You’ll often encounter
properties that can be set in Design view but become read-only when the program is
running.
One example of a read-only property is the Height property of the Combo Box control.
Although you can view the value of the Height property in the Properties window,
you can’t change the value—no matter how hard you try. If you attempt to
change the Height property using Visual Basic code, Visual Basic simply changes the
value back to the default—eerie gremlins.
Understanding Properties 61
The best way to determine which properties of an object are read-only is to consult
the online help for the object in question.
By the
Way
Working with an Object and Its Properties
Now that you know what properties are and how they can be viewed and changed,
you’ll experiment with properties by modifying the Picture Viewer project you built in
Hour 1. Recall from Hour 1 how you learned to set the Height and Width properties
of a form in the Properties window. Here, you’ll change the same properties, now
using Visual Basic code.
You’ll add two buttons to your Picture Viewer. One button will enlarge the form when
clicked, and the other will shrink the form. This is a simple example, but it illustrates
well how to change object properties in Visual Basic code.
Start by opening your Picture Viewer project from Hour 1. If you download the code
samples from my site, I provide a Picture Viewer project for you to start with. Doubleclick
ViewerForm.vb in the Solution Explorer window to show the form designer.
When the project first runs, the form has the Height and Width you specified in the
Properties window. You’ll add buttons to the form that a user can click to enlarge or
shrink the form at runtime by following these steps:
1. Add a new button to the form by double-clicking the Button tool in the toolbox.
Set the new button’s properties as follows:
2. Now for the Shrink button. Again, double-click the Button tool in the toolbox to
create a new button on the form. Set this new button’s properties as follows:
Property Value
Name btnEnlarge
Location 338,261
Size 21,23
Text ^ (This is Shift+6.)
Property Value
Name btnShrink
Location 359,261
Size 21,23
Text v
62 HOUR 3: Understanding Objects and Collections
Your form should now look like the one in shown in Figure 3.2.
To complete the project, you need to add the small amount of Visual Basic code
necessary to modify the form’s Height and Width properties when the user
clicks a button.
3. Access the code for the Enlarge button by double-clicking the ^ button. Type the
following statement exactly as you see it here. Do not press the Enter key or add
a space after you’ve entered this text:
Me.Width
When you type the period, or dot, as it’s called, a small drop-down list like the
one shown in Figure 3.3 appears. Visual Basic is smart enough to realize that
Me represents the current form (more on this in a moment). To help you write
code for the object, it gives you a drop-down list containing all the properties
and methods of the form. This feature is called IntelliSense. When an IntelliSense
drop-down box appears, you can use the up and down arrow keys to
navigate the list and press Tab to select the highlighted list item. This prevents
you from misspelling a member name, thereby reducing compile errors.
Because Visual Basic is fully object-oriented, you’ll come to rely on IntelliSense
drop-down lists in a big way; I think I’d rather dig ditches than program without
them.
FIGURE 3.2
Each button is
an object, as is
the form on
which the buttons
sit.
Understanding Properties 63
By the
Way
FIGURE 3.3
IntelliSense
drop-down lists
(also called autocompletion
dropdown
lists) make
coding dramatically
easier.
4. Use the Backspace key to erase the code you just entered, and enter the following
code in its place (press Enter at the end of each line):
Me.Width = Me.Width + 20
Me.Height = Me.Height + 20
Remember from before that the word Me doesn’t refer to a person, it refers to the
object to which the code belongs (in this case, the form). Me is a reserved word;
it’s a word that you can’t use to name objects or variables because Visual Basic
has a specific meaning for it. When writing code within a form module, as
you’re doing here, always use the reserved word Me rather than the name of the
form. Me is much shorter than using the full name of the current form, and it
makes the code more portable. (You can copy and paste the code into another
form module and not have to change the form name to make the code work.)
Also, should you change the name of the form at any time in the future, you
won’t have to change references to the old name.
Me works only in object-based modules such as form modules; you can’t use Me
in a standard module, which you’ll learn about in Hour 10, “Creating and Calling
Code Procedures.”
The code you just entered does nothing more than set the form’s Width and
Height properties to their current value plus 20 pixels.
64 HOUR 3: Understanding Objects and Collections
5. Redisplay the form designer by selecting the tab named ViewerForm.vb [Design]
at the top of the designer window. Then double-click the button with the v to
access its Click event, and add the following code:
Me.Width = Me.Width - 20
Me.Height = Me.Height - 20
This code is similar to the code in the btnEnlarge_Click event, except that it
reduces the form’s Width and Height properties by 20 pixels. Your screen
should now look like Figure 3.4.
As you create projects, it’s a good idea to save frequently. When an asterisk
appears to the right of a tab’s title (as you can see in Figure 3.4), you know that
the file edited within that tab has been changed but not saved. Save your project
now by clicking the Save All button on the toolbar.
Did you
Know?
Again, display the form designer by clicking the tab ViewerForm.vb [Design]. Your
Properties Example project is now ready to be run! Press F5 to put the project in Run
mode. Before continuing, click the Select Picture button, and choose a picture from
your hard drive.
Next, click the ^ button a few times and notice how the form gets bigger (see Figure 3.5).
FIGURE 3.4
The code you’ve
entered should
look exactly like
this.
Understanding Methods 65
Next, click the v button to make the form smaller. When you’ve clicked enough to
satisfy your curiosity (or until you get bored), end the running program, and return to
Design mode by clicking the Stop Debugging button on the toolbar.
Did you notice how the buttons and the image on the form didn’t resize as the form’s
size changed? In Hour 6, “Building Forms: Advanced Techniques,” you’ll learn how to
make your forms resize their contents.
Understanding Methods
In addition to properties, most objects have methods. Methods are actions the object
can perform, in contrast to attributes, which describe the object. To understand this
distinction, think about the pet object example one more time. A Dog object has a
certain set of actions it can perform. These actions, called methods in Visual Basic,
include barking, tail wagging, and chewing carpet (don’t ask). Figure 3.6 illustrates
the Dog object and its methods.
FIGURE 3.5
The form gets
bigger, but it still
looks just as you
designed it.
66 HOUR 3: Understanding Objects and Collections
Dog Object
Bark
WagTail
Eat
Walk
Fetch
Methods
FIGURE 3.6
Invoking a
method causes
the object to perform
an action.
Triggering Methods
Think of methods as functions—which is exactly what they are. When you invoke a
method, code is executed. You can pass data to a method, and methods can return
values. However, a method is not required to accept parameters (data passed to it by
the calling code) or return a value; many methods simply perform an action in code.
Invoking (triggering) a method is similar to referencing the value of a property. First
you reference the object’s name, and then provide a dot, and then the method name:
ObjectName.Method
For example, to make the hypothetical Dog object Bruno bark using Visual Basic code,
you would use this line of code:
Bruno.Bark()
Methods generally are used to have an object perform an action, such as saving
or deleting a record in a database. Properties, on the other hand, are used to get
and set the object’s attributes. One way to tell in code whether a statement is a
property reference or method call is that a method call has a set of parentheses
after it, like this:
AlbumForm.ShowDialog()
By the
Way
Building a Simple Object Example Project 67
Invoking methods is simple; the real skill lies in knowing what methods an object
supports and when to use a particular method.
Understanding Method Dynamism
Properties and methods go hand in hand, and at times a particular method might
become unavailable because of one or more property values. For example, if you were
to set the NumberofLegs property on the Dog object Bruno equal to 0, the Walk() and
Fetch() methods obviously would be inapplicable. If you were to set the NumberofLegs
property back to 4, you could then trigger the Walk() or Fetch() methods again.
Building a Simple Object Example Project
The only way to really grasp what objects are and how they work is to use them. I’ve
said this before, but I can’t say it enough: Everything in Visual Basic 2010 is an
object. This fact has its good points and bad points. One of the bad points is that in
some instances, it takes more code to accomplish a task than it did in the past—
sometimes more characters, sometimes more statements. If you’re moving from
Visual Basic 6, you have some learning and adjusting ahead of you, but it’s worth it!
Every project you’ve built so far uses objects, but now you’ll create a sample project
that specifically illustrates using objects. If you’re new to programming with objects,
you’ll probably find this a bit confusing. However, I’ll walk you through step by step,
explaining each section in detail.
You’ll modify your Picture Viewer project to include a button that, when clicked,
draws a colored border around the picture. You’ll get a taste of some drawing functions
in this example. Don’t worry; you’re not expected to understand all the intricacies
of the drawing code. Your sole responsibility is grasping how objects work.
Creating the Interface for the Drawing Project
Continuing with the Picture Viewer project you’ve been using in this chapter, add a
new button to the form, and set its properties as follows:
Property Value
Name btnDrawBorder
Location 295,69
Size 85,23
Text Draw Border
68 HOUR 3: Understanding Objects and Collections
Writing the Object-Based Code
Now you’ll add code to the button’s Click event. I’ll explain each statement, and at
the end of the steps, I’ll show the complete code listing. Follow these steps to create
the code that draws the border:
1. Double-click the Draw Border button to access its Click event.
2. Enter the first line of code as follows (remember to press Enter at the end of each
statement):
Dim objGraphics As Graphics
Here you’ve just created a variable that will hold an instance of an object. Objects
don’t materialize out of thin air; they have to be created. When a form is loaded into
memory, it loads all its controls (that is, it creates the control objects), but not all
objects are created automatically as they are in this situation. The process of creating
an instance of an object is called instantiation. When you load a form, you instantiate
the form object, which in turn instantiates its control objects. You could load a second
instance of the form, which in turn would instantiate a new instance of the form and
new instances of all controls. You would then have two forms in memory, and two of
each used control.
To instantiate an object in code, you create a variable that holds a reference to an
instantiated object. The Dim statement you wrote in step 2 creates a new variable
called objGraphics, which holds a reference to an object of type Graphics. You’ll
learn more about variables in Hour 11.
Next, enter the second line of code exactly as shown here:
objGraphics = Me.CreateGraphics
CreateGraphics is a method of the form. (Remember, the keyword Me is shorthand
for referencing the current form.) Under the hood, the CreateGraphics method is
pretty complicated. For now, understand that the method CreateGraphics instantiates
a new object that represents the client area of the current form. The client area is
the gray area within a form’s borders and title bar. Anything drawn on the
Building a Simple Object Example Project 69
objGraphics object appears on the form. What you’ve done is set the variable
objGraphics to point to an object that was returned by the CreateGraphics method.
Notice how values returned by a property or method don’t have to be traditional values
such as numbers or text; they could also be objects.
Enter the third line of code:
objGraphics.Clear(SystemColors.Control)
This statement clears the form’s background using whatever color the user has
selected as the Windows Control color, which Windows uses to paint forms.
How does this happen? After declaring the objGraphics object, you used the
CreateGraphics method of the form to instantiate a new graphics object in the variable
objGraphics. With the code statement you just entered, you’re calling the
Clear() method of the objGraphics object. The Clear() method is a method of all
Graphics objects used to clear the graphic surface. The Clear() method accepts a
single parameter: the color you want used to clear the surface.
The value you’re passing to the parameter might seem a bit odd. Remember that
“dots” are a way of separating objects from their properties and methods. (Properties,
methods, and events are often called object members.) Knowing this, you can discern
that SystemColors is an object because it appears before any of the dots. Object references
can and do go pretty deep, and you’ll use many dots throughout your code.
The key points to remember are
. Text that appears to the left of a dot is always an object (or namespace).
. Text that appears to the right of a dot is a property reference or method call. If
the text is followed by parentheses, it’s a method call. If not, it’s most likely a
property.
. Methods can return objects, just as properties can. The only surefire ways to
know whether the text between two dots is a property or method are to look at
the icon of the member in the IntelliSense drop-down or to consult the object’s
documentation.
The final text in this statement is the word Control. Because Control isn’t followed
by a dot, you know that it’s not an object; therefore, it must be a property or method.
You expect this string of object references to return a color value to be used to clear
the graphic object. Therefore, you know that Control in this instance must be a property
or method that returns a value (because you need the return value to set the
Clear() method). A quick check of the documentation would tell you that Control is
indeed a property. The value of Control always equates to the color designated on
the user’s computer for the face of forms and buttons. By default, this is a light gray
70 HOUR 3: Understanding Objects and Collections
(often fondly referred to as battleship gray), but users can change this value on their
computers. By using this property to specify a color rather than supplying the actual
value for gray, you’re assured that no matter the color scheme used on a computer,
the code will clear the form to the proper system color.
Enter the following statement. (Note: Do not press Enter until you’re finished entering
all the code shown here. The code appears on two lines only because of the size
restriction of this page.)
objGraphics.DrawRectangle(Pens.Blue, picShowPicture.Left - 1,
picShowPicture.Top - 1, picShowPicture.Width + 1, picShowPicture.Height + 1)
This statement draws a blue rectangle around the picture on the form. Within this
statement is a single method call and five property references. Can you tell what’s
what? Immediately following objGraphics (and a dot) is DrawRectangle. Because
no equals sign is present but there is an open parenthesis, you can deduce that this is
a method call. As with the Clear() method, the parentheses after DrawRectangle
are used to enclose values passed to the method.
The DrawRectangle() method accepts the following parameters in the order in
which they appear here:
. A pen
. X value of the upper-left corner
. Y value of the upper-left corner
. Width of the rectangle
. Height of the rectangle
The DrawRectangle() method draws a prefect rectangle using the X, Y, Width, and
Height values passed to it. The attributes of the line (color, width, and so on) are
determined by the pen specified in the Pen parameter. (I won’t go into detail on pens
here; check the online help if pens interest you.) Looking at the dots once more, notice
that you’re passing the Blue property of the Pens object. Blue is an object property
that returns a predefined Pen object that has a width of 1 pixel and the color blue.
For the next two parameters, you pass property values. Specifically, you pass the top
and left values for the picture, less 1. If you passed the exact left and top values, the
rectangle would be drawn on the form at exactly the top and left properties of the
PictureBox. You wouldn’t see them because controls by default overlap any drawing
performed on the form.
Building a Simple Object Example Project 71
The last two property references are for the height and width of the PictureBox.
Again, we adjust the values by 1 to ensure that the rectangle is drawn outside the
borders of the PictureBox.
Finally, you have to clean up after yourself by entering the following code statement:
objGraphics.Dispose()
Objects often use other objects and resources. The underlying mechanics of an object
can be mind-boggling and are almost impossible to discuss in an entry-level programming
book. The net effect, however, is that you must explicitly destroy most
objects when you’re finished with them. If you don’t destroy an object, it might persist
in memory, and it might hold references to other objects or resources that exist in
memory. This means that you can create a memory leak within your application that
slowly (or rather quickly) munches system memory and resources. This is one of the
cardinal no-no’s of Windows programming. However, the nature of using resources
and the fact that you’re responsible for telling your objects to clean up after themselves
make this easy to do. If your application causes memory leaks, your users
won’t call for a plumber, but they might reach for a monkey wrench—in an effort to
smack you upside the head!
Objects that must explicitly be told to clean up after themselves usually provide a
Dispose() method. When you’re finished with such an object, call Dispose() on the
object to make sure that it frees any resources it might be holding.
For your convenience, here are all the lines of code:
Dim objGraphics As Graphics
objGraphics = Me.CreateGraphics
objGraphics.Clear(System.Drawing.SystemColors.Control)
objGraphics.DrawRectangle(System.Drawing.Pens.Blue, _
picShowPicture.Left - 1, picShowPicture.Top - 1, _
picShowPicture.Width + 1, picShowPicture.Height + 1)
objGraphics.Dispose()
The statement calling DrawRectangle() is shown here as three lines of code. At
the end of the first and second lines is an underscore character (_), also known
as a line continuation character. It tells the Visual Basic compiler that the statement
immediately following the character is a continuation of the current statement.
You can, and should, use this character to break up long statements in
your code.
By the
Way
Click Save All on the toolbar to save your work before continuing.
72 HOUR 3: Understanding Objects and Collections
Testing Your Object Example Project
Now the easy part: Run the project by pressing F5 or by clicking the Start button on
the toolbar. Your form looks pretty much as it did at design time. Clicking the button
causes a blue rectangle to be drawn around the PictureBox, as shown in Figure 3.7.
If you receive any errors when you attempt to run the project, go back and make
sure that the code you entered exactly matches the code I’ve provided.
If you use Alt+Tab to switch to another application after drawing the rectangle, the
rectangle will be gone when you come back to your form. In fact, this occurs any
time you overlay the graphics with another form. In Hour 18, “Working with Graphics,”
you will learn how to persist images so that they don’t disappear when the
form becomes obscured.
By the
Way
Stop the project now by clicking Stop Debugging on the Visual Basic toolbar. What I
hope you’ve gained from building this example is not necessarily that you can now
draw a rectangle (which is cool), but rather an understanding of how objects are used
in programming. As with learning almost anything, repetition aids understanding.
That said, you’ll be working with objects a lot throughout this book.
Understanding Collections
A collection is just what its name implies: a collection of objects. Collections make it
easy to work with large numbers of similar objects by enabling you to create code
that performs iterative processing on items within the collection. Iterative processing is
an operation that uses a loop to perform actions on multiple objects, rather than
requiring you to write the operative code for each object. In addition to containing an
indexed set of objects, collections have properties and might have methods. Figure 3.8
illustrates the structure of a collection.
FIGURE 3.7
You can create
simple lines and
complex drawings
by using
objects.
Understanding Collections 73
Collection
Objects
Properties
Methods
Properties
Methods
FIGURE 3.8
Collections contain
sets of like
objects, and they
have their own
properties and
methods.
Continuing with the Dog/Pet object metaphor, think about what an Animals collection
might look like. The Animals collection might contain one or more pet objects,
or it might be empty (contain no objects). All collections have a Count property that
returns the total count of objects contained in the collection. Collections might also
have methods, such as a Delete() method used to remove objects from the collection,
and an Add() method used to add a new object to the collection.
To better understand collections, you’ll create a small Visual Basic project that cycles
through the Controls collection of a form and tells you the value of the Name property
of every control on the form. To create your sample project, follow these steps:
1. Start Visual Basic (if it’s not already loaded), and create a new Windows Application
project titled Collections Example.
2. Change the form’s filename to CollectionsExampleForm.vb using the Solution
Explorer (right-click Form1.vb in the Solution Explorer and choose
Rename), and set the form’s Text property to Collections Example in the Properties
window (you need to click the form to view its properties).
3. Add a new button to the form by double-clicking the Button tool in the toolbox.
Set the button’s properties as follows:
Property Value
Name btnShowNames
Location 88, 112
Size 120, 23
Text Show Control Names
74 HOUR 3: Understanding Objects and Collections
4. Next, add some Text Box and Label controls to the form. As you add the controls
to the form, be sure to give each control a unique name. Feel free to use
any name you want, but you can’t use spaces in a control name. You might want
to drag the controls to different locations on the form so that they don’t overlap.
5. When you’re finished adding controls to your form, double-click the Show Control
Names button to add code to its Click event. Enter the following code:
Dim intIndex As Integer
For intIndex = 0 To Me.Controls.Count - 1
MessageBox.Show(“Control #” & intIndex & “ has the name “ & _
Me.Controls(intIndex).Name)
Next intIndex
Every form has a Controls collection, which might not contain any controls; even
if no controls are on the form, the form still has a Controls collection.
By the
Way
The first statement of the preceding code should look familiar to you by now. As with
the Object example you created earlier, this statement creates a variable to hold a
value. Rather than create a variable that can hold an object, as you did in the earlier
example, this statement creates a variable that can hold only a number.
The next statement (the one that begins with For) accomplishes a few tasks. First, it
initializes the variable intIndex to 0, and then it starts a loop (loops are discussed in
Hour 14, “Looping for Efficiency”). It increments intIndex by 1 until intIndex
equals the number of controls on the form, less 1. The reason you subtract 1 from the
Count property is that collections are 0-based—the first item is always item 0. Thus,
the first item is in index 0, the second item is in location 1, and so forth. If you tried
to reference an item of a collection in the location of the value of the Count property,
an error would occur. You would be referencing an index that’s 1 higher than the
actual locations within the collection.
The MessageBox.Show() method (mentioned in Hour 2 and discussed in detail in
Hour 17, “Interacting with Users”) is a class of the .NET Framework that’s used to display
simple dialog boxes with text. The text that you’re providing, which the Show()
method displays, is a concatenation of multiple strings of text. (Concatenation is the
process of adding strings together; it’s discussed in Hour 12, “Performing Arithmetic,
String Manipulation, and Date/Time Adjustments.”)
Run the project by pressing F5 or by clicking Start on the toolbar. Ignore the additional
controls that you placed on the form, and click the Show Control Names button.
Your program then displays a message box similar to the one shown in Figure
3.9 for each control on your form (because of the loop). When the program is finished
displaying the names of the controls, choose Debug, Stop Debugging to stop
the program, and then save the project.
Using the Object Browser 75
FIGURE 3.9
The Controls collection
enables
you to get to
every control on
a form.
Because everything in Visual Basic 2010 is an object, you can expect to use numerous
collections as you create your programs. Collections are powerful, and the
quicker you become comfortable using them, the more productive you’ll be.
Using the Object Browser
Visual Basic 2010 includes a useful tool that enables you to easily view members
(properties, methods, and events) of all the objects in a project: the Object Browser
(see Figure 3.10). This is useful when you’re dealing with objects that aren’t well documented
because it enables you to see all the members an object supports. To view
the Object Browser, press F2. The Object Browser should also be available from the
View menu, but it is not visible in the beta 2 release I am using for this book.
FIGURE 3.10
The Object
Browser enables
you to view all
properties and
methods of an
object.
76 HOUR 3: Understanding Objects and Collections
The Browse drop-down list in the upper-left corner of the Object Browser is used to
determine the browsing scope. You can choose My Solution to view only the objects
referenced in the active solution, or you can choose All Components to view all possible
objects. You can customize the object set by clicking the drop-down arrow next to
the Object Browser Settings button to the far right of the Browse drop-down list. I
don’t recommend changing the custom object setting until you have some experience
using Visual Basic .NET objects, as well as experience using the Object Browser.
The top-level nodes (each item in the tree is called a node) in the Objects tree are
libraries. Libraries are usually DLL or EXE files on your computer that contain one or
more objects. To view the objects in a library, simply expand the library node. As you
select objects within a library, the list to the right of the Objects tree shows information
about the members of the selected object (refer to Figure 3.10). For even more
detailed information, click a member in the list on the right. The Object Browser
shows information about the member in the area below the member list.
Summary
In this hour, you learned a lot about objects. You learned how objects have properties,
which are attributes that describe the object. Some properties can be set at
design time in the Properties window, and most can also be set at runtime in Visual
Basic code. You learned that referencing a property on the left side of the equals sign
has the effect of changing the property, whereas referencing a property on the right
side of the equals sign retrieves the property’s value.
In addition to properties, you learned that objects have executable functions, called
methods. Like properties, methods are referenced by using a dot at the end of an
object reference. An object might contain many methods and properties, and some
properties can even be objects themselves. You learned how to “follow the dots” to
interpret a lengthy object reference.
Objects are often used as a group, called a collection. You learned that a collection
often contains properties and methods, and that collections let you easily iterate
through a set of like objects. Finally, you learned that the Object Browser can be used
to explore all the members of an object in a project.
The knowledge you’ve gained in this hour is fundamental to understanding programming
with Visual Basic, because objects and collections are the basis on which
applications are built. After you have a strong grasp of objects and collections—and
you will have by the time you’ve completed all the hours in this book—you’ll be well
on your way to fully understanding the complexities of creating robust applications
with Visual Basic .NET.
Workshop 77
Q&A
Q. Is there an easy way to get help about an object’s member?
A. Absolutely. Visual Basic’s context-sensitive Help extends to code as well as
visual objects. To get help on a member, write a code statement that includes
the member (it doesn’t have to be a complete statement), position the cursor
within the member text, and press F1. For instance, to get help on the Integer
data type, you could type Integer, position the cursor within the word
Integer, and press F1.
Q. Are there any other types of object members besides properties and methods?
A. Yes. An event is actually a member of an object, although it’s not always
thought of that way. Although not all objects support events, most objects do
support properties and methods.
Workshop
Quiz
1. True or false: Visual Basic 2010 is a true object-oriented language.
2. An attribute that defines the state of an object is called a ____________.
3. For you to change the value of a property, the property must be referenced on
which side of the equals sign?
4. What is the term for when a new object is created from a template class?
5. An external function of an object (one that is available to code manipulating
an object) is called a ____________.
6. True or false: A property of an object can be another object.
7. A group of like objects is called a ____________.
8. What tool is used to explore the members of an object?
78 HOUR 3: Understanding Objects and Collections
Answers
1. True
2. Property
3. The left side
4. Instantiation
5. Method
6. True
7. Collection
8. The Object Browser
Exercises
1. Create a new project, and add two text boxes and a button to the form. Write
code that, when a button is clicked, places the text in the first text box into the
second text box. Hint: Use the Text property of the TextBox controls.
2. Modify the collections example in this hour to print the height of all controls,
rather than the name.
Understanding Event-Driven Programming 79
HOUR 4
Understanding Events
What You’ll Learn in This Hour:
. Understanding event-driven programming
. Triggering events
. Avoiding recursive events
. Accessing an object’s events
. Working with event parameters
. Creating event handlers
. Keeping event names current
It’s easy to produce an attractive interface for an application with Visual Basic 2010’s
integrated design tools. You can create beautiful forms that have buttons to click,
text boxes in which to type information, picture boxes that display pictures, and
many other creative and attractive elements with which users can interact. However,
that’s just the start of producing a Visual Basic program. In addition to designing an
interface, you have to empower your program to perform actions in response to both
how a user interacts with the program and how Windows interacts with the program.
This is accomplished through the use of events. In Hour 3, “Understanding Objects
and Collections,” you learned about objects and their members—notably, properties
and methods. In this hour, you’ll learn about object events and event-driven programming,
and you’ll learn how to use events to make your applications responsive.
Understanding Event-Driven
Programming
With traditional programming languages (often called procedural languages), the program
itself fully dictates what code is executed, as well as when it’s executed. When
you start such a program, the first line of code in the program executes, and the code
80 HOUR 4: Understanding Events
continues to execute in a completely predetermined path. The execution of code
might branch and loop on occasion, but the execution path is wholly determined by
the program. This often means that such a program is restricted in how it can
respond to the user. For example, the program might expect text to be entered into
controls on the screen in a predetermined order. This is unlike a Windows application,
in which a user can interact with different parts of the interface—often in any
order he or she chooses.
Visual Basic 2010 incorporates an event-driven programming model. Event-driven
applications aren’t bound by the constraints of procedural programs. Instead of the
top-down approach of procedural languages, event-driven programs have logical
sections of code placed within events. Events don’t occur in a predetermined order;
the user often has complete control over what code is executed in an event-driven
program by interactively triggering specific events, such as by clicking a button.
Triggering Events
In Hour 3, you learned that a method is simply a function of an object. An event, in
a sense, is really a special kind of method used by an object to signal state changes
that might be useful to clients (code using the object). In fact, the Visual Basic 2010
documentation often calls events methods (something that no doubt confuses new
programmers). Events are methods that can be called in special ways—usually by the
user interacting with something on a form or by Windows itself—rather than being
called from a statement in your code.
There are many types of events and many ways to trigger them. You’ve already seen
how a user can trigger the event of a button by clicking it. User interaction isn’t the
only thing that can trigger an event; an event can be triggered in one of the following
four ways:
. Users can trigger events by interacting with your program. Clicking a button,
for example, triggers the button’s Click event.
. Objects can trigger their own events as needed. The Timer control, for example,
can trigger its Timer event at regular intervals.
. The operating system (whichever version of Windows the user is running) can
trigger events.
. You can trigger events by calling them much as you would invoke a method
when using Visual Basic code.
Understanding Event-Driven Programming 81
Events Triggered Through User Interaction
The most common way an event is triggered is when a user interacts with a program.
Every form, and almost every control you can place on a form, has a set of events
specific to its object type. The Button control, for example, has a number of events,
including the Click event you’ve already used in previous hours. When the user
clicks a button, the button’s Click event is triggered, and then the code within the
Click event executes.
The Textbox control enables users to enter information with the keyboard, and it
also has a set of events. The Textbox control has some of the same types of events as
the Button control, such as a Click event, but the Textbox control also has events
not supported by the Button control, such as the MultilineChanged event. The
MultilineChanged event occurs when the Multiline property of the text box
changes. Because you can’t enter text into a Button control, it doesn’t have a
Multiline property and therefore no MultilineChanged event. Every object that
supports events supports a unique set of events.
Each type of event has its own behavior, and it’s important to understand the events
you work with. The TextChanged event, for example, exhibits a behavior that might
not be intuitive to a new developer because the event fires each time the contents of
the text box change. Consider what would happen if you were to type the following
sentence into an empty text box in a project you created:
www.ChemicalEcho.com
Although it’s easy to think that the TextChanged event fires only when you commit
your entry, such as by leaving the text box or pressing Enter, this isn’t how it works.
Instead, the TextChanged event would be triggered 20 times—once for each character
typed—because each time you enter a new character, the contents of the text box
change. Again, it’s important to learn the nuances and the exact behavior of the
events you’re using. If you use events without fully understanding how they work,
your program might exhibit unusual (which usually means undesirable) results.
Events Triggered by an Object
Sometimes an object triggers its own events. The most common example of this is the
Timer control’s Tick event. The Timer control is a nonvisual control like the common
dialog control. It doesn’t appear on a form when the program is running; it
appears at design time in the space reserved for nonvisual controls. The Timer control’s
sole purpose is to trigger its Tick event at an interval specified in its Interval
property.
82 HOUR 4: Understanding Events
By setting the Timer control’s Interval property, you control the interval (in milliseconds)
at which the Timer event executes. After firing its Timer event, a Timer
control resets itself and fires its Timer event again when the interval has passed. This
occurs until the interval is changed, the Timer control is disabled, or the Timer control’s
form is unloaded. A common use of timers is to create a clock on a form. You
can display the time in a label and update it at regular intervals by placing the code
to display the current time in the Timer event. You’ll create a project with a Timer
control in Hour 8, “Using Advanced Controls.”
Events Triggered by the Operating System
The third way an event can be triggered is by Windows itself. Often, you might not
even realize these events exist. For example, when a form is fully or partially
obstructed by another window, the program needs to know when the offending window
is resized or moved so that it can repaint the area of the window that’s hidden.
Windows and Visual Basic work together in this respect. When the obstructing window
is moved or resized, Windows tells Visual Basic to repaint the form, which Visual
Basic does. This also causes Visual Basic to raise the form’s Paint event. You can
place code into the Paint event to create a custom display for the form, such as
drawing shapes on the form with a Graphics object. When you do so, your custom
drawing code executes every time the form repaints itself.
Avoiding Recursive Events
You must ensure that you never create code where an event can endlessly trigger
itself. This is called a recursive event. To illustrate a situation that causes a recursive
event, think of the Textbox control’s TextChanged event, discussed earlier. The
TextChanged event fires every time the text in the text box changes. Placing code in
the TextChanged event that alters the text in the text box causes the Change event to
be fired again, which could result in an endless loop. Recursive events terminate
when Windows returns a StackOverflow exception (see Figure 4.1), indicating that
Windows no longer has the resources to follow the recursion.
Recursive behavior can occur with more than one event in the loop. For example, if
Event A triggers Event B, which in turn triggers Event A, you can have infinite looping
of the two events. Recursive behavior can take place among a sequence of many
events, not just one or two.
Uses for recursive procedures actually exist, such as when writing complex math
functions. For instance, recursive events are often used to compute factorials.
However, when you purposely create a recursive event, you must ensure that the
recursion isn’t infinite.
By the
Way
Understanding Event-Driven Programming 83
FIGURE 4.1
When you
receive a Stack-
Overflow exception,
you should
look for a recursive
event as the
culprit.
Accessing an Object’s Events
Accessing an object’s events is simple. If you’ve been following the examples in this
book, you’ve already accessed a number of objects’ default events. To access an
object’s events, you double-click the object in Form Design view.
You’ll now create a project to get a feel for working with events. Start Visual Basic
2010, create a new Windows Application project titled View Events, and then follow
these steps:
1. Right-click Form1.vb in the Solutions Explorer and choose Rename. Change the
filename to ViewEventsForm.vb. Next, change the Text property of the form
to View Events Example.
2. Use the toolbox to add a picture box to the form.
3. Change the name of the picture box to picText, and then double-click the picture
box to access its event procedures.
Your screen should look like the one shown in Figure 4.2. Notice the two combo boxes
at the top of the code window. One contains the word picText, and the other reads
Click. The combo box on the left contains a list of all the objects of the current form
84 HOUR 4: Understanding Events
FIGURE 4.2
Use the events
drop-down list in
the code editor
to create event
procedures.
(including the form itself and all its controls). The combo box on the right contains
all the events for the object selected in the first drop-down list.
Currently, you’re viewing the Click event for the picText object. The cursor is placed
within the Click event procedure, ready for you to enter code. The code statement
above the cursor is the event declaration—a statement that defines the structure of an
event. Notice that this event declaration contains the name of the object, an underscore
character (_), and then the event name. Following the event name is a set of parentheses.
The items within the parentheses are called parameters, which are the topic of the
next section. This is the standard declaration structure for an event procedure.
Click the events drop-down list (the list on the right), and take a look at all the events
that the picture box supports. Select MouseDown from the list, and notice how your
code window changes to look like the one shown in Figure 4.3.
When you select an event from the list, Visual Basic creates a new event procedure for
that event. The full event declaration is shown here:
Private Sub picText_MouseDown(ByVal sender As Object, _
ByVal e As System.Windows.Forms.MouseEventArgs) _
Handles picText.MouseDown
Notice that the new event declaration is similar to the first one in the window in that
it’s titled with the object’s name followed by an underscore. However, the remainder
of the event procedure declaration is different. It’s the name of the event—in this case,
MouseDown.
Understanding Event-Driven Programming 85
FIGURE 4.3
Visual Basic creates
an empty
event procedure
the first time you
select an
object’s event.
The words Private and Sub are Visual Basic reserved words that indicate the
scope and type of the procedure. Scope and type are discussed in Hour 10, “Creating
and Calling Code Procedures.”
By the
Way
Working with Event Parameters
As mentioned previously, the items within the parentheses of an event declaration
are called parameters. An event parameter is a variable that’s created and assigned a
value by Visual Basic. These parameter variables are used to get, and sometimes set,
relevant information within the event. This data may be text, a number, an object—
almost anything. Multiple parameters within an event procedure are always separated
by commas. As you can see, the MouseDown event has two parameters. When
the event procedure is triggered, Visual Basic automatically creates the parameter
variables and assigns them values for use in this single execution of the event procedure.
The next time the event procedure occurs, the values in the parameters are
reset. You use the values in the parameters to make decisions or perform operations
in your code.
The MouseDown event of a form has the following parameters:
ByVal sender As Object
and
ByVal e As System.Windows.Forms.MouseEventArgs
86 HOUR 4: Understanding Events
For now, ignore the ByVal keywords. These are discussed in Hour 11, “Using Constants,
Data Types, Variables, and Arrays.”
The text following ByVal is the name of the parameter, and the string after the word
As indicates the type of data the parameter contains. The first parameter, sender,
holds a generic object. Object parameters can be any type of object supported by
Visual Basic. Some contain text, others contain numbers, and still others (many others)
contain objects. In the case of the sender parameter, it always holds a reference
to the control causing the event.
The e parameter of the MouseDown event, on the other hand, is where the real action
is. The e parameter also holds an object, and in this case the object is of type
System.Windows.Forms.MouseEventArgs. This object has properties that relate to
the MouseDown event. To see them, type in the following code, but don’t press anything
after entering the dot (period):
e.
When you enter the period, you get a drop-down list showing you the members
(properties and methods) of the e object, as shown in Figure 4.4. Using the e object,
you can determine a number of things about the occurrence of the MouseDown event.
Table 4.1 lists some of the more interesting items.
FIGURE 4.4
IntelliSense
drop-down lists
alleviate the
need to memorize
the makeup
of hundreds of
objects.
Building an Event Example Project 87
Each time the event occurs, Visual Basic initializes the parameters so that they
always reflect the current occurrence of the event.
By the
Way
Each event has parameters specific to it. For instance, the TextChanged event returns
parameters that are different from the MouseDown event. As you work with events—
and you’ll work with a lot of events—you’ll quickly become familiar with the parameters
of each event type. You’ll learn how to create parameters for your own functions
and procedures in Hour 10.
Building an Event Example Project
You’ll now learn how to use the MouseMove event by modifying the Picture Viewer
project of Hour 3. You’ll make it so that, as a user moves the mouse over a picture,
the cursor’s x- and y-coordinates are displayed on the form. You’ll use the e parameter
to get the coordinates of the mouse pointer.
Go ahead and open the Picture Viewer project you completed in Hour 3 now. If
prompted to save your changes, answer No. If you don’t have this project, you can
download it from my website.
TABLE 4.1 Commonly Used Members of System.Windows.Forms.
MouseEventArgs
Property Description
Clicks Returns the number of times the user clicked the mouse button.
Button Returns the button that was clicked (left, middle, right).
Delta Returns a positive or negative number indicating the number of
clicks performed (forward or backward) with the mouse wheel.
X Returns the horizontal coordinate at which the pointer was located
when the user clicked.
Y Returns the vertical coordinate at which the pointer was located
when the user clicked.
Location Returns a Point object that contains the X and Y coordinates at
which the pointer was located when the user clicked.
88 HOUR 4: Understanding Events
Creating the User Interface
You’ll need two Label controls on the form—one for the X value and one for the Y
value. Label controls are used to display static text; users can’t type text into a label.
Add a Label control to the form by double-clicking the Label tool in the toolbox. Set
its properties as follows:
Use the toolbox to add one more Label control to the form. Set its properties as follows:
Your form should now look like the one shown in Figure 4.5. It’s a good idea to save
frequently, so save your project now by clicking the Save All button on the toolbar.
Property Value
Name lblY
Location 300, 125
Text Y:
Property Value
Name lblX
Location 300, 110
Text X:
FIGURE 4.5
Label controls
display static
text to the user.
Building an Event Example Project 89
Creating Event Handlers
The interface for this example is complete—now on to the fun part. You’ll now create
the event procedures that empower the program to do something. The first event that
we’re interested in is the MouseMove event. Double-click the picture box on the form
to access its event procedures. When you double-click a control, the event procedure
that’s created is always for the default event for the type of control. For picture boxes,
this is the Click event. We’re not interested in the Click event at this time, however.
Open the event list (the drop-down list in the upper right), and then select MouseMove
in the list. Visual Basic creates a new MouseMove procedure for the text box.
Notice that Visual Basic left the default event procedure it created for you. It’s best not
to leave dead code (code that isn’t used), so delete the Click event procedure now.
To fully delete the event procedure, you must delete all the following code:
Private Sub picShowPicture_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) _
Handles picShowPicture.Click
End Sub
After you’ve deleted the procedure, your code should look like Figure 4.6.
Now, place the cursor on the line between the Private Sub and End Sub statements
of the picShowPicture_MouseMove procedure.
FIGURE 4.6
Each time you
select a new
event, Visual
Basic creates an
empty event procedure—
if one
wasn’t created
previously for the
control.
90 HOUR 4: Understanding Events
Enter the following code into the MouseMove event procedure:
lblX.Text = “X: “ & e.X
lblY.Text = “Y: “ & e.Y
This code is simple, and it may already make sense to you. If it’s still not clear, it will
be soon. Consider the first line of code (called a statement). lblX.Text is on the left of
the equals sign, so Text is a property of the label, and you’ll set it to some value. The
text ”X: “ is a literal value that we’re placing in the Text property of the Label control.
The reason you include this literal is that when you set the Text property, you
overwrite the property’s current value. So, even though you entered X: as the property
in the properties window, you need to include it when setting the property as well. To
make this useful, we also have to include the actual value for X, which is stored in the
X property of the e object. Again, we’re concatenating the literal value of ”X: “ with the
value stored in e.X. The second statement does the same thing, only with the Y value.
The nice thing about objects is that you don’t have to commit every detail about
them to memory. For example, you don’t need to memorize the return values for each
type of button. (Who wants to remember e.X, e.Y, or e.Button, anyway?) Just
remember that the e parameter contains information about the event. When you
type e and press the period, the IntelliSense drop-down list appears and shows you
the members of e. Don’t feel overwhelmed by all the object references you’ll
encounter throughout this book. Simply accept that you can’t memorize them all, nor
do you need to; you’ll learn the ones that are important, and you’ll use Help when
you’re stuck. Also, after you know the parent object in a situation (such as the e
object in this example), it’s easy for you to determine the objects and members that
belong to it by using the IntelliSense drop-down lists.
Click the Save All button in the toolbar to save your work. (You wouldn’t want to lose
it!) Next, press F5 to run the project, and move the mouse pointer over the picture
box. You’ll see the coordinates of the pointer (as it relates to the picture box) displayed
in the two Label controls you created, as shown in Figure 4.7.
Now, move the mouse pointer off the picture box. Notice that the labels display the
last coordinate that the pointer moved over on the picture box. The MouseMove event
fires only when the mouse pointer is moved over the control to which the event is
attached: the picture box in this example. We can’t just leave those numbers dangling
there, can we?
The PictureBox just so happens to have another event you can use to fix this: the
MouseLeave event. Oddly enough, the MouseLeave event fires when the mouse
pointer leaves the control’s space. (Woot—something that’s actually intuitive!) Follow
these steps to clear the coordinates when the pointer leaves the picture box:
Building an Event Example Project 91
FIGURE 4.7
The MouseMove
event makes it
easy to track the
pointer over a
control.
1. Stop the project if it’s still running by closing the Picture Viewer form.
2. Open the Events drop-down list for the picShowPicture control, and choose
MouseLeave.
3. Enter the following code into the MouseLeave event:
lblX.Text = ““
lblY.Text = ““
Press F5 to run the project again. Move the mouse pointer over the picture box and
then off it. Notice that the coordinates go away. Move the pointer over the picture
box again, and they reappear—perfect! Go ahead and stop the running project now.
There’s only one thing left to do. Did you notice that when you first start the project,
the labels have “X:” and “Y:” in them? Wouldn’t it be better to not display this text
until the user mouses over the picture box? You could set the Text properties of these
labels to empty by using the Properties window. However, if you do this, you won’t see
the labels on the form in the designer and may place other controls over the top of
them. A better solution is to initialize their values when the form first loads. You’ll do
just that by following these steps:
1. Open the object drop-down list in the upper left and select (ViewerForm Events).
This is the object reference to your form (see Figure 4.8).
2. Open the event drop-down list in the upper-right corner and choose Load. The
Load event executes automatically when the form first loads—the perfect place
to initialize the Label controls.
92 HOUR 4: Understanding Events
FIGURE 4.8
The form itself
always appears
at the top of the
object list.
3. Enter the following two code statements:
lblX.Text = ““
lblY.Text = ““
That’s it—you’re finished! Go ahead and press F5 to run the project and give it a test
drive. When the form first loads, the coordinate labels should be empty (this makes
them appear invisible). When you mouse over the picture box, the coordinates are
displayed, and when you leave the confines of the picture box, the coordinates are
hidden again. A little bit of code and the right event selection can go a long way.
Keeping Event Names Current
If you’ve used any version of Visual Basic prior to 2010, you’ve undoubtedly experienced
orphaned events. As you know, the name of an event procedure is defined by
the control’s name, followed by an underscore and then the event name (such as
txtAddress_TextChanged). When you change the name of a control, Visual Basic
doesn’t change the control’s event declarations to reflect the new name, but it does
keep the event attached to the control. The way this works is that at the end of each
event declaration is the keyword Handles, followed by an object name. The Handles
keyword effectively “hooks up” an event handler to the event of a control. When you
change the name of a control, Visual Basic changes the Handles reference, but it
Q&A 93
doesn’t change the event name itself. Although your code will work, you should manually
change the name of the corresponding procedures so that they match the new
name of the control. This will help a lot when you debug complicated code.
Although Visual Basic doesn’t update the name of event procedures when you
change the name of a control, it updates any references to the control you have in
other procedures. This is a great time-saving feature that is relatively new to
Visual Basic.
Did you
Know?
Summary
In this hour, you learned about event-driven programming, including what events
are, how to trigger them, and how to avoid recursive events. In addition, you learned
how to access an object’s events and how to work with parameters. Much of the code
you write will execute in response to an event of some kind, and you’ll often write
code for multiple events of one control. By understanding how events work, including
being aware of the available events and their parameters, you’ll be able to create
complex Visual Basic programs that react to a multitude of user and system input.
Q&A
Q. Is it possible to create custom events for an object?
A. Yes, you can create custom events for your own objects (you’ll learn about such
objects in Hour 16, “Designing Objects Using Classes”), and you can also create
them for existing objects. Creating custom events, however, is beyond the scope
of this book.
Q. Is it possible for objects that don’t have an interface to support events?
A. Yes. To use the events of such an object, however, the object variable must be
dimensioned a special way, or the events aren’t available. This gets a little
tricky and is beyond the scope of this book. If you have an object in code that
supports events, look in Help for the keyword WithEvents for information on
how to use such events.
94 HOUR 4: Understanding Events
Workshop
Quiz
1. Name three things that can cause events to occur.
2. True or false: All objects support the same set of events.
3. What is the default event type for a button?
4. What is it called when you write code in an event that causes that same event
to be triggered, setting off a chain reaction, with the event triggered repeatedly?
5. What is the easiest way to access a control’s default event handler?
6. All control events pass a reference to the control causing the event. What is the
name of the parameter that holds this reference?
7. What should you do when you change a control’s name?
Answers
1. User input, system input, and other code
2. False
3. Click
4. Recursion
5. Double-click the control in the form designer
6. sender
7. Change the name of its defined events accordingly
Exercises
1. Use the knowledge you’ve gained so far to create a new project with a form
that is gray at design time but that appears blue when it is displayed.
2. Create a project with a form and a text box. Add code to the TextChange event
to cause a recursion when the user types in text. Hint: Concatenate a character
to the end of the user’s text, using a statement such as
txtMyTextBox.Text = txtMyTextBox.Text & “a”
The ampersand tells Visual Basic to add the letter a to the end of the existing
text box contents. Notice how you eventually get a Stack Over-Flow error—not
a good thing!
95
HOUR 5
Building Forms: The Basics
What You’ll Learn in This Hour:
. Changing a form’s name
. Changing a form’s appearance
. Displaying text on a form’s title bar
. Adding an image to a form’s background
. Giving a form an icon
. Changing the mouse pointer
. Showing and hiding forms
. Displaying a form in a normal, maximized, or minimized state
. Specifying a form’s initial display position
. Preventing a form from appearing in the taskbar
With few exceptions, forms are the cornerstone of every Windows application interface.
Forms are essentially windows, and the two terms are often used interchangeably.
More accurately, window refers to what the user sees and interacts with, whereas
form refers to what you see when you design. Forms enable users to view and enter
information in a program (such as the form you built in your Picture Viewer program
in Hour 1, “Jumping in with Both Feet: A Visual Basic 2010 Programming
Tour”). Such information may be text, pictures, graphs—almost anything that can
be seen on the screen. Understanding how to design forms correctly enables you to
begin creating solid interface foundations for your programs.
Think of a form as a canvas on which you build your program’s interface. On this
canvas, you can print text, draw shapes, and place controls with which users can
interact. The wonderful thing about Visual Basic forms is that they behave like a
dynamic canvas. Not only can you adjust a form’s appearance by manipulating
what’s on it, you also can manipulate specific properties of the form itself.
96 HOUR 5: Building Forms: The Basics
In previous hours, you manipulated the following form appearance properties:
. Text
. Height
. Left
. Top
. Width
The ability to tailor your forms goes far beyond these basic property manipulations,
as you’ll see.
There’s so much to cover about Windows forms that I’ve broken the material into two
hours. In this hour, you’ll learn the basics of forms—adding them to a project,
manipulating their properties, and showing and hiding them using Visual Basic
code. Although you’ve done some of these things in previous hours, here you’ll learn
the nuts and bolts of the tasks you’ve performed. In the next hour, you’ll learn more
advanced form techniques.
Changing a Form’s Name
The first thing you should do when you create a new object is give it a descriptive
name, so that’s the first thing I’ll talk about in this hour. Start by opening the Picture
Viewer project you completed in Hour 4, “Understanding Events.” If you don’t have
this project, you can download it from my website.
Your Picture Viewer currently has some useful functionality, but it’s not very flexible.
In this hour, you’ll start building an Options dialog box for the program. Add a new
form for the dialog box by following these steps:
1. Choose Project, Add Windows Form to display the Add New Item dialog box.
2. In the Name text box, enter Optionsform.vb. This will be the name of your
form as well as the name of the file that defines the form on the hard drive.
3. Click the Add button (or double-click the Windows Form icon) to close the Add
New Item dialog box and add the form to your project (see Figure 5.1).
You can use the Properties window to change the name of a form at any time. Doing
so changes the form’s Name property (but not the name of the file on the hard disk).
Whenever possible, give your forms solid names when creating them.
Changing a Form’s Appearance 97
FIGURE 5.1
Each new form
starts off as a
blank canvas.
Changing a Form’s Appearance
The Properties window can actually show two different sets of properties for a form.
Right now, it’s probably showing the form’s file properties (the properties that
describe the physical file[s] on the hard drive, as shown in Figure 5.2). If so, click the
form in the designer again to view its development properties. Clicking the form itself
shows the form’s development properties, whereas clicking the form’s name in the
Solution Explorer shows you the form’s physical file properties. This is why I usually
tell you to click the form before setting its properties.
Take a moment to browse the form’s properties in the Properties window. In this hour,
I’ll show you how to use the form’s more common properties to tailor its appearance.
Displaying Text on a Form’s Title Bar
You should always set the text in a form’s title bar to something meaningful. (Not all
forms have title bars, as you’ll see later in this hour.) The text displayed in the title
bar is the value placed in the form’s Text property. Generally, the text should be one
of the following:
. The name of the program: This is most appropriate when the form is the
program’s main or only form. You used the name of the program for your
main form when you defined it in Hour 1.
98 HOUR 5: Building Forms: The Basics
FIGURE 5.2
File properties
can be useful,
but they don’t
allow you to do
much with the
form.
. The purpose of the form: This is perhaps the most common type of text displayed
in a title bar. For example, if a form is used to select a printer, consider
setting the Text property to Select Printer. When you take this approach, use
active voice (for instance, don’t use Printer Select).
. The name of the form: If you choose to place the form’s name in the form’s
title bar, use the English name, not the actual form name. For instance, if
you’ve used a naming convention and you named a form LoginForm, use the
text Login or User Login.
Change the Text property of your form to Picture Viewer Options. Remember, you
may have to click the form to select it and see its properties. Your form should now
look like the one shown in Figure 5.3.
As with most other form properties, you can change the Text property at any time
using Visual Basic code.
By the
Way
Changing a Form’s Background Color
Although most forms appear with a gray background (this is part of the standard 3D
color scheme in Windows), you can change a form’s background to any color you
want. To change a form’s background color, you change its BackColor property. The
Changing a Form’s Appearance 99
FIGURE 5.3
Use common
sense when setting
title bar
text.
BackColor property is a unique property in that you can specify a named color or an
RGB value in the format red, green, blue.
By default, the BackColor property is set to the color named Control. This color is a
system color and might not be gray. When Windows is installed, it’s configured to a
default color scheme. In the default scheme for all Windows versions earlier than XP,
the color for forms and other objects is the familiar “battleship gray.” For XP, Vista,
and Windows 7 installations, this color is a light tan (although it still looks gray on
most monitors). As a Windows user, you’re free to change any system color you want.
For instance, some people with color blindness prefer to change their system colors to
colors that have more contrast than the defaults so that objects are more clearly distinguishable.
When you assign a system color to a form or control, the object’s
appearance adjusts itself to the current user’s system color scheme. This doesn’t just
occur when a form is first displayed; changes to the system color scheme are immediately
propagated to all objects that use the affected colors.
Try to use system colors whenever possible. This will make your application
behave as closely as possible to what the user expects and will avoid problems
such as using colors that are indistinguishable from one another to someone who
is color-blind.
By the
Way
Change your form’s background color by deleting the word Control in the
BackColor property in the Properties window. In its place, enter 0,0,255 and press
100 HOUR 5: Building Forms: The Basics
Enter or Tab to commit your entry. When you commit the entry, the RGB value
changes to the word Blue. If Visual Basic has a named color that matches your RGB
values, it automatically switches to the name for you.
Your form should now be blue, because you entered an RGB value in which you specified
no red, no green, and maximum blue (color values range from 0 to 255). In reality,
you’ll probably rarely enter RGB values. Instead, you’ll select colors from color
palettes. To view color palettes from which you can select a color for the BackColor
property, click the drop-down arrow in the BackColor property in the Properties window,
as shown in Figure 5.4.
By the System colors are discussed in detail in Hour 18, “Working with Graphics.”
Way
When the drop-down list appears, the color blue is selected on the Web tab. Again,
this happens because when you enter the RGB value 0,0,255, Visual Basic looks for a
named color composed of the same values and finds blue. The color palettes were
explained in Hour 2, “Navigating Visual Basic 2010,” so I won’t go into detail about
them here. For now, select the System tab to see a list of the available system colors.
Choose Control from the list to change your form’s BackColor property back to the
default Windows color.
Adding an Image to a Form’s Background
In addition to changing the color of a form’s background, you can place a picture on
it. To add a picture to a form, set the form’s BackgroundImage property. When you
add an image to a form, the image is painted on the form’s background. All the controls
that you place on the form appear on top of the picture.
Add an image to your form by following these steps:
1. Click the form to select it.
FIGURE 5.4
All color properties
have
palettes from
which you can
choose a color.
Changing a Form’s Appearance 101
2. Change the form’s Size property to 400, 300.
3. Click the BackgroundImage property in the Properties window.
4. Click the Build button that appears next to the property (the small button with
three dots).
5. The Select Resource dialog box appears, as shown in Figure 5.5. Click the Local
Resource option button.
6. Click Import and locate the file Options.bmp, which you can get from downloading
the example files from my website.
7. You are returned to the Select Resource dialog box. Click OK to load the picture.
The selected image is displayed on the form’s background, as shown in Figure 5.6.
If the image you select is smaller than the form, Visual Basic displays additional
copies of the picture, creating a tiled effect. The image you just selected was specifically
made to be the same size as the form, so you don’t have to worry about this.
Notice that to the left of the BackgroundImage property in the Properties window is a
small box containing a triangle. This indicates that the BackgroundImage property
has related properties, or subproperties. Click the triangle to expand the list of subproperties,
as shown in Figure 5.7. In the case of the BackgroundImage property,
Visual Basic shows you a number of properties related to the image assigned to the
property, such as its dimensions and image format. Note that these subproperties are
read-only (with the exception of the Tag property); not all subproperties are read-only.
Adding a background image to a form can add pizzazz to a program, but it can
also confuse users by making the form unnecessarily busy. Try to avoid adding
images just because you can. Use discretion, and add an image to a form only
when the image adds value to the interface.
Did you
Know?
FIGURE 5.5
Images on your
hard drive are
considered local
resources.
102 HOUR 5: Building Forms: The Basics
FIGURE 5.6
A form can display
a picture,
just as a picture
box does.
FIGURE 5.7
The subproperties
show you
details about the
image.
Removing an image from a form is just as easy as adding the image in the first place.
To remove the picture you just added to your form, right-click the BackgroundImage
property name and choose Reset from the shortcut menu that appears. You must
right-click the Name column of the property or right-click the Build button in the
Value column, but don’t right-click the Value column itself. If you right-click the property’s
value, you get a different shortcut menu that doesn’t have a Reset option. Feel
free to try this, but load the image again before continuing.
Changing a Form’s Appearance 103
Giving a Form an Icon
The icon assigned to a form appears on the left side of the form’s title bar, in the
taskbar when the form is minimized, and in the iconic list of tasks when you press
Alt+Tab to switch to another application, as well as in other places. The icon often
represents the application; therefore, you should assign an icon to any form that a
user can minimize. If you don’t assign an icon to a form, Visual Basic supplies a
default icon to represent the form when it’s minimized. This default icon is generic
and unattractive and doesn’t really represent anything; you should avoid it.
In the past, it was recommended that every form have a unique icon that represented
the form’s purpose. This proved difficult to accomplish in large applications containing
dozens or even hundreds of forms. Instead, it’s usually just best to set the Icon
property of all your forms to the icon that best represents your application. Because
you used the Properties window to set the icon of the main form in Hour 1, you’ll use
that icon again, but you’ll do it with Visual Basic code. To assign the main icon to
your form, follow these steps:
1. Double-click the form in the Form Designer to access its default event: the
Load event.
2. Enter the following code statement into the Load event:
Me.Icon = ViewerForm.Icon
Recall from earlier that Me represents the form in which the code resides—your Options
form. This code sets the Options form icon to the icon of the Picture Viewer form (your
main form). Now, if you change the icon of the main form in design view, you can be
certain that the Options form will always appear with the proper icon. If you were to use
the Properties window to set an icon for the Options form, you would lose this flexibility.
Adding Minimize, Maximize, and Control Box
Buttons to a Form
Click the OptionsForm.vb [Design]* tab at the top of the work area to switch to the
Form Designer. Take a look at the title bar of the Picture Viewer Options form that
you’ve created, and notice that it has three buttons on it, as shown in Figure 5.8.
The three buttons in the form’s title bar are
. Minimize
. Maximize
. Close
104 HOUR 5: Building Forms: The Basics
FIGURE 5.8
You control
which, if any, of
these buttons
are displayed.
Also note that the form’s icon acts as a button as well, but only while the application
is running, not while it is in design mode. If the user clicks the icon, a drop-down
menu appears with some basic options, as shown in Figure 5.9.
The Minimize and Maximize buttons make it easy for a user to quickly hide a form or
make it fill the entire display, respectively. You’ve probably used these buttons on
applications you work with. You’ll be happy to know that you don’t have to write
code to implement this—Windows handles it automatically. All you have to do is
decide whether you want a Maximize or Minimize button on a form. In the case of
this Options form, the contents won’t be resizable, so there’s no need for a Maximize
button. Also, you’ll want the user to close the form when she’s finished with it, so
there’s no need for a Minimize button either. To remove these buttons, set the following
properties of the form:
FIGURE 5.9
A form’s icon
acts like a
button.
Property Value
MinimizeBox False
MaximizeBox False
Changing a Form’s Appearance 105
If you don’t want the user to be able to close the form with the Close button (the button
with the X in the upper-right corner of the form), you would set the ControlBox
property to False. Be aware, however, that the Minimize and Maximize buttons are
hidden automatically when ControlBox is set to False. If you want a Minimize or
Maximize button, you have to set ControlBox = True.
Changing the Appearance and Behavior of a
Form’s Border
You might have noticed while working with other Windows programs that the borders
of forms can vary. Some forms have borders that you can click and drag to
change the size of the form, some have fixed borders that can’t be changed, and still
others have no borders at all. The appearance and behavior of a form’s border are
controlled by its FormBorderStyle property.
The FormBorderStyle property can be set to one of the following values:
. None
. FixedSingle
. Fixed3D
. FixedDialog
. Sizable
. FixedToolWindow
. SizableToolWindow
Run your project now by pressing F5, and move the mouse pointer over one of the
borders of your main Picture Viewer form. This form has a sizable border, which
means that you can resize the form by dragging the border. Move the pointer over an
edge of the form. Notice how the pointer changes from a large arrow to a line with
arrows pointing to either side, indicating the direction in which you can stretch the
border. When you move the pointer over a corner, you get a diagonal cursor that
indicates that you can stretch both of the sides that meet at the corner. Clicking and
dragging the border changes the size of the form.
Stop the project now by choosing Debug, Stop Debugging (or click the Close button
on the form), and change the OptionsForm form’s FormBorderStyle property to
None. Notice that the title bar disappears as well, as shown in Figure 5.10. Of course,
when the title bar is gone, there’s no visible title bar text, no control box, and no Minimize
or Maximize buttons. In addition, there’s no way to move or resize the form. It’s
rarely appropriate to specify None for a form’s BorderStyle, but if you need to do so
(a splash screen comes to mind), Visual Basic 2010 makes it possible.
106 HOUR 5: Building Forms: The Basics
FIGURE 5.10
A form with no
border also has
no title bar.
Next, change the OptionsForm form’s FormBorderStyle property to
FixedToolWindow. This setting causes the form’s title bar to appear smaller than normal
and the text to be displayed in a smaller font, as shown in Figure 5.11. In addition,
the only thing displayed on the title bar besides the text is a Close button. Visual
Basic’s various design windows, such as the Properties window and the toolbox, are
good examples of tool windows.
FIGURE 5.11
A tool window is
a special window
whose title bar
takes up the
minimum space
possible.
Showing and Hiding Forms 107
The FormBorderStyle offers a good example of how changing a single property can
greatly affect an object’s appearance and behavior. Set the form’s FormBorderStyle
back to FixedSingle before continuing.
Controlling a Form’s Minimum and Maximum Size
Ordinarily, if a form can be resized, it can be maximized to fill the user’s entire display.
The form can be minimized right down to the taskbar as well. If you want to
restrict a form’s minimum or maximum size, set the MinimumSize or MaximumSize
properties, respectively. In general, you should avoid doing this, but it can be useful.
Be aware that setting a specific MinimumSize doesn’t stop the user from minimizing
the form if it has a minimize button.
Showing and Hiding Forms
Part III, “Making Things Happen: Programming,” is devoted to programming in
Visual Basic 2010. I’ve avoided going into much programming detail in this hour so
that you can focus on the concepts at hand. However, knowing how to create forms
does nothing for you if you don’t have a way to show and hide them. Visual Basic
2010 can display a single form automatically only when a program starts. To display
other forms, you have to write code.
Showing Forms
There are a couple of ways to show a form, and you’ll learn about the most common
methods in this section.
Now you’ll make it so that the user of your Picture Viewer program can display the
Options form you’ve built. Follow these steps to add this functionality to your program:
1. Double-click ViewerForm.vb in the Solution Explorer to display the main form
in the designer.
2. Right-click the Draw Border button, and choose Copy from the shortcut menu.
3. Right-click the form (somewhere below the X and Y labels) and choose Paste.
4. Set the properties of your new button as follows:
Property Value
Name btnOptions
Location 295, 155
Text Options
108 HOUR 5: Building Forms: The Basics
5. Double-click the Options button to access its Click event.
6. Enter the following code:
OptionsForm.Show()
Press F5 to run the project, and click the Options button. The Options form appears
on top of the main Picture Viewer form. Click the title bar of the Picture Viewer form
(the form in the background). Notice how this brings the Picture Viewer form to the
front and obscures the Options form. There will be times when you want this behavior.
However, many times you won’t. For most forms, it’s desirable to force the focus to
the form with which the user is working and make the user dismiss the form before
working with another. In the next section, you’ll learn how to change this behavior.
Stop the running project before continuing.
Understanding Form Modality
You can present two types of forms to the user: modal and nonmodal. A nonmodal
window is one that doesn’t cause other windows to be disabled. (When you used
Show() to display the Options form, you displayed it as a nonmodal form. This is
why you could click over to the main Picture Viewer form while the Options form
remained displayed.) Another example of a nonmodal window is the Find and
Replace window in Word (and in Visual Basic 2010, as well). When the Find and
Replace window is visible, the user can still access other windows.
On the other hand, when a form is displayed as a modal form, all other forms in the
same application become disabled until the modal form is closed; the other forms
won’t accept any keyboard or mouse input. The user is forced to deal with only the
modal form. After the modal form is closed, the user is free to work with other visible
forms within the program. If the form was displayed by another modal form, that
form retains the focus until closed, and so on. Modal forms are most often used to create
dialog boxes in which the user works with a specific set of data and controls
before moving on. The Print dialog box of Microsoft Word, for example, is a modal
dialog box. When the Print dialog box is displayed, you can’t work with the document
on the main Word window until the Print dialog box is closed. Most secondary
windows in any given program are modal windows.
Showing and Hiding Forms 109
You can display one modal form from another modal form, but you cannot display
a nonmodal form from a modal form.
By the
Way
A form’s modality is determined by how you show the form rather than by how you
create it. (Both modal and nonmodal forms are created the same way.) You already
learned that to show a form as a nonmodal window, you use the form’s Show()
method. To show a form as a modal form, you call the form’s ShowDialog() method
instead. Change the code in your button’s Click event to read as follows:
OptionsForm.ShowDialog()
When your code looks like this, press F5 to run the project. Click the Options button
to display your Options form. Drag the form away from the main form just a bit, and
then try to click the main Picture Viewer form or some control on it; you can’t. Close
the modal form now by clicking the Close button in the title bar. Now the main Picture
Viewer form is enabled again, and you can click the Options button once more
(or any other button of your choosing). When you’re finished testing this, stop the
running project.
You can test to see whether a form has been shown modally by testing the form’s
Modal property in code.
Did you
Know?
Displaying a Form in a Normal, Maximized, or
Minimized State
Using a form’s Size and Location properties in conjunction with the StartPosition
property enables you to display forms at any location and at any size. You can also
force a form to appear minimized or maximized. Whether a form is maximized, minimized,
or shown normally is known as the form’s state, and it’s determined by the
form’s WindowState property.
Click the OptionsForm.vb [Design] tab to view the form designer. Look at your form’s
WindowState property now in the Properties window. New forms have their
WindowState property set to Normal by default. When you run the project, as you
have several times, the form displays in the same size as that in which it appears in
the form designer and at the location specified by the form’s Location property. Now
change the WindowState property to Minimized. Nothing happens in the Form
Design view, but run your project by pressing F5, and then click the Options button.
At first, you might think the form didn’t get displayed, but it did. It just appeared
minimized to the taskbar.
110 HOUR 5: Building Forms: The Basics
Stop the project and change the WindowState property to Maximized. Again, nothing
happens in the Form Design view. Press F5 to run the project, and then click the
Options button. This time, the Options form fills the screen. Notice too how the image
is tiled to fill the form (see Figure 5.12), as explained when you added the image to
the form.
When a form is maximized, it fills the entire screen, regardless of the current
screen resolution being used in Windows.
By the
Way
Stop the project, and change the WindowState property back to Normal. You’ll rarely
set a form’s WindowState property to Minimize at design time (although you might
specify Maximize), but you’ll probably encounter situations in which you need to
change (or determine) the WindowState at runtime. As with most properties, you can
accomplish this using code. For example, the following statement would minimize
the Options form:
OptionsForm.WindowState = FormWindowState.Minimized
You don’t have to remember the names of the values when entering code; you’ll get
an IntelliSense drop-down list when you type the equals sign.
FIGURE 5.12
Images placed
on a form are
tiled if the form’s
BackgroundIma
geLayout property
is set to
Tiled.
Showing and Hiding Forms 111
Specifying a Form’s Initial Display Position
The location on the display (monitor) where a form first appears isn’t random; it is
controlled by the form’s StartPosition property. The StartPosition property can
be set to one of the values described in Table 5.1.
It’s generally best to set the StartPosition property of all your forms to
CenterParent unless you have a specific reason to do otherwise. For the first
form that appears in your project, you might consider using the
WindowsDefaultLocation (but I generally prefer CenterScreen).
By the
Way
To see how this property affects a form, try this:
1. Press F5 to run the project.
2. Move the Picture Viewer form, and click the Options button. Notice where the
Options form appears.
3. Close the Options form.
4. Move the Picture Viewer form to the upper-right corner, and click the Options
button again.
Did you notice that the Options form always appears in the same location, regardless
of where the Picture Viewer form is placed when the Options button is clicked? I’m
not fond of this behavior. Stop the running project, and change the StartPosition
TABLE 5.1 Values for the StartPosition Property
Value Description
Manual The value of the Location property at
design time determines where the
form first appears.
CenterScreen The form appears centered in the display.
WindowsDefaultLocation The form appears in the Windows default
location, which is toward the upper left of
the display.
WindowsDefaultBounds The form appears in the Windows default
location with its bounds (size) set to the
Windows default bounds.
CenterParent The form is centered within the bounds of
its parent form (the initial form that
displayed the form in question).
112 HOUR 5: Building Forms: The Basics
of the Options form to CenterParent. Next, repeat the previous steps. You’ll see that
the Options form always appears centered over the Picture Viewer form, regardless of
where that form is positioned.
Stop the project now, and save your work.
Preventing a Form from Appearing in the Taskbar
Being able to display an icon for a minimized form is nice, but sometimes it’s necessary
to prevent a form from even appearing in the taskbar. If your application has a
number of tool windows that float over a main window, such as the Solutions
Explorer and toolbox in Visual Basic 2010, for example, it’s unlikely that you’d want
any but your main form to appear in the taskbar. To prevent a form from appearing
in the taskbar, set the form’s ShowInTaskbar property to False. If the user minimizes
a form with its ShowInTaskbar property set to False, he can still get to the application
by pressing Alt+Tab even though the program can’t be accessed via the taskbar;
Visual Basic doesn’t allow the application to become inaccessible to the user.
Unloading Forms
After a form has served its purpose, you’ll want it to go away. However, go away can
mean one of two things. First, you can make a form disappear without closing it or
freeing its resources (this is called hiding). To do so, you set its Visible property to
False. This hides the visual part of the form, but the form still resides in memory and
can still be manipulated by code. In addition, all the form’s variables and controls
retain their values when a form is hidden, so if the form is displayed again, it looks
the same as it did when its Visible property was set to False.
The second method closes a form and releases the resources it consumes. You should
close a form when it’s no longer needed so that Windows can reclaim all resources
used by the form. To do so, you invoke the Close() method of the form like this:
Me.Close()
In Hour 3, “Understanding Objects and Collections,” you learned how Me is used to
reference the current Form object. Because Me represents the current Form object, you
can manipulate properties and call methods of the current form using Me.
(Me.Visible = False, and so forth).
The Close() method tells Visual Basic not to simply hide the form but to destroy
it—completely.
Showing and Hiding Forms 113
Follow these steps to create a button to close the Options form:
1. Select the OptionsForm.vb [Design] tab to display the form designer for the
Options form (if it isn’t displayed already).
2. Add a new button to the form, and set its properties as follows:
Property Value
Name btnOK
Location 305, 12
Size 75, 23
Text OK
3. Double-click the OK button in the designer to access its Click event, and then
enter the following statement:
Me.Close()
4. Run the project by pressing F5. Click the Options button to display the Options
form, and then click OK to close the Options form. Again, the form isn’t just
hidden; it is completely unloaded from memory and no longer exists.
If you simply wanted to hide a form, but not unload it from memory, you would call
the Hide() method of the form or set the form’s Visible property to False. This
would preserve the state of the form for the time you choose to show it again.
By the
Way
114 HOUR 5: Building Forms: The Basics
Summary
In this hour, you learned the basics of creating forms. You learned how to add them
to your project, set basic appearance properties, and show and hide them using
Visual Basic code. In the next hour, you’ll learn more advanced functionality for
working with forms. After you’ve mastered the material in this hour and the next,
you’ll be ready to dig into Visual Basic’s controls. That’s where the fun of building an
interface really begins!
Q&A
Q. How many form properties should I define at design time as opposed to
runtime?
A. You should set all the properties that you can at design time. First, it will be
easier to work with the form, because you can see exactly what the user will
see. Also, debugging is easier, because there’s less code.
Q. Should I let the user minimize and maximize all forms?
A. Probably not. There’s no point in letting a form be maximized if it isn’t set up
to adjust its controls accordingly. About dialog boxes, print dialog boxes, and
spell-check windows are examples of forms that should not be resizable.
Workshop
Quiz
1. True or false: The text displayed in the form’s title bar is determined by the
value in the TitleBarText property.
2. The named color Control is what kind of color?
3. Name three places where a form’s icon is displayed.
4. What is a window with a smaller-than-normal title bar called?
5. For a Minimize or Maximize button to be visible on a form, what other element
must be visible?
6. In general, what is the best value to use for a form’s StartPosition property?
Workshop 115
7. To maximize, minimize, or restore a form in code, you set what property?
8. What property do you set to make a hidden form appear?
Answers
1. False. The text displayed in the form’s title bar is determined by the value in
the form’s Text property.
2. A system color
3. In the title bar, on the task bar, and when the user presses Alt+Tab
4. The Tool window
5. The form’s ControlBox property must be set to True.
6. CenterScreen for the main form and CenterParent for all other forms
7. The form’s WindowState property
8. Set the form’s Visible property to True.
Exercises
1. Create a Windows Application project with a single form that has two buttons.
One button, when clicked, should move the form to the left by two pixels. The
other should move the form to the right by two pixels. Hint: Use the form’s
Left property.
2. Create a Windows Application with three forms. Give the startup form two buttons.
Make the other two forms tool windows, and make one button display
the first tool window and the other button display the second tool window.
This page intentionally left blank
Working with Controls 117
HOUR 6
Building Forms: Advanced
Techniques
What You’ll Learn in This Hour:
. Adding controls to a form
. Positioning, aligning, sizing, spacing, and anchoring controls
. Creating intelligent tab orders
. Adjusting the z-order of controls
. Creating forms that always float over other forms
. Creating transparent forms
. Creating multiple-document interfaces
A form is just a canvas, and although you can tailor a form by setting its properties,
you need to add controls to make it functional. In the previous hour, you learned
how to add forms to a project, set basic form properties, and show and hide forms. In
this hour, you’ll learn about adding controls to a form, including arranging and
aligning controls to create an attractive and functional interface. You’ll also learn
how to create advanced multiple-document interfaces (MDIs) as used in applications
such as Photoshop. After you complete the material in this hour, you’ll be ready to
learn the specifics about the various controls available in Visual Basic.
Working with Controls
Controls are the objects that you place on a form for users to interact with. If you’ve
followed the examples in the previous hours, you’ve already added controls to a
form. However, you’ll be adding a lot of controls to forms, and it’s important for you
to understand all aspects of the process.
118 HOUR 6: Building Forms: Advanced Techniques
By the
Way
Adding Controls to a Form
All the controls that you can add to a form can be found in the toolbox. The toolbox
appears as a docked window on the left side of the design environment by default.
This location is useful when you only occasionally add controls to forms. However,
when doing serious form-design work, I find it best to dock the toolbox to the right
edge of the design environment, where it doesn’t overlap so much (if any) of the
form I’m working with.
Remember that before you can undock a toolbar to move it to a new location, you
must make sure that it isn’t set to Auto Hide.
The toolbox has category headings that you can expand and collapse. For most of
your design, you’ll use the controls in the Common Controls category. As your skills
progress, however, you might find yourself using more complex and highly specialized
controls found in the other categories.
You can add a control to a form in four ways. You’ve already learned to paste a copy
of a control onto a form. In this chapter, you will use the other three methods for
adding a control to the form. Open the Picture Viewer project you created in the previous
hour (or open the starting project provided at my website), and double-click
OptionsForm.vb in the Solution Explorer window to view the Options form in the
designer.
Adding a Control by Double-Clicking It in the Toolbox
The easiest way to add a control to a form is to double-click the control in the toolbox.
Try this now: Display the toolbox and double-click the TextBox tool. Visual Basic
creates a new text box in the upper-left corner of the form (you have to move the
mouse away from the toolbox to close the toolbox and see the new control). When
you double-click a control in the toolbox (excluding controls that are invisible at runtime),
Visual Basic creates the new control on top of the control that currently has the
focus. It has the default size for the type of control you’re adding. If no other controls
are on the form, the new control is placed in the upper-left corner, as you’ve seen
here. After the control is added to the form, you’re free to move and size the control
as you please.
Adding a Control by Dragging from the Toolbox
If you want a little more authority over where a new control is placed, you can drag a
control to the form. Try this now: Display the toolbox, click the Button control, and
Working with Controls 119
drag it to the form. When the cursor is roughly where you want the button created,
release the mouse button.
Adding a Control by Drawing It
The last and most precise method of placing a control on a form is to draw the control
on a form. Follow these steps:
1. Display the toolbox and click the ListBox tool to select it.
2. Move the pointer to where you want the upper-left corner of the list box to
appear, and then click and hold the mouse button.
3. Drag the pointer to where you want the bottom-right corner of the list box to be
and release the button.
The list box is created, with its dimensions set to the rectangle you drew on the form.
This is by far the most precise method of adding controls to a form.
If you prefer to draw controls on your forms by clicking and dragging, I strongly
suggest that you float the toolbox or dock it to the right or bottom edge of the
design environment. The toolbox interferes with drawing controls when it’s docked
to the left edge, because it obscures a good bit of the underlying form.
Did you
Know?
It’s important to note that the first item in each tool category is titled Pointer. Pointer
isn’t actually a control. When the Pointer item is selected, the design environment is
placed in Select mode rather than in a mode to create a new control. With the pointer
chosen, you can select a control and view its properties simply by clicking it in the
designer. This is the default behavior of the development environment.
Manipulating Controls
Getting controls on a form is the easy part. Arranging them so that they create an
intuitive and attractive interface is the challenge. Interface possibilities are nearly
endless, so I can’t tell you how to design any given interface here (but I strongly suggest
that you create forms that closely match the appearance and behavior of similar
commercial applications). However, I can show you the techniques to move, size, and
arrange controls so that they appear the way you want them to. By mastering these
techniques, you’ll be much more efficient at building interfaces, freeing your time for
writing the code that makes things happen.
120 HOUR 6: Building Forms: Advanced Techniques
Using the Grid (Size and Snap)
You may have noticed as you’ve worked with controls in this book that controls seem
to “snap” to an invisible grid. You’re not crazy—they actually do. When you draw or
move a control on a form in a project with grids enabled, the coordinates of the control
automatically snap to the nearest grid coordinates. This offers some precision
when adjusting the size and location of controls. In practical use, I often find the grid
to be only slightly helpful, because the size or location I want often doesn’t fit neatly
with the grid locations. However, you can control the grid’s granularity and even visibility,
and I suggest you do both.
Grid settings are global to Visual Basic—you don’t set them for each individual project
or form. To display the grid settings on your computer, choose Tools, Options to
display the Options form. Next, click Windows Forms Designer in the tree on the left
to view the designer settings, as shown in Figure 6.1.
The settings we’re interested in here are as follows:
. GridSize determines the granularity of the grid in pixels both horizontally and
vertically. A smaller grid size means that you have finer control over control
size and placement.
. LayoutMode determines whether the designer snaps a control you are moving
to the grid or aligns it with other controls.
. ShowGrid determines whether grid dots are displayed on forms in the designer.
. SnapToGrid determines whether the grid is used. If this setting is False, the
grid size setting is ignored, and nothing is snapped to the grid.
FIGURE 6.1
Grid settings are
global to Visual
Basic 2010.
Working with Controls 121
Right now, you’re not using the grid for drawing controls, but you are using snap
lines when moving controls because your LayoutMode is set to SnapLines. I’ll talk
about this in more detail later in this section. Right now, I want to show you how
grids work, so change your LayoutMode setting to SnapToGrid.
Now you’ll assign a higher level of granularity to the grid (the space between the grid
points will be smaller). I find that this helps with design because edges aren’t so easily
snapped to unwanted places.
To adjust the grid’s granularity, you change the GridSize setting. Setting the grid’s
Width or Height to a smaller number creates a more precise grid, which gives you
finer control over sizing and placement. Using larger values creates a much coarser
grid and offers less control. With a larger grid, you’ll find that edges snap to grid
points much more easily and at larger increments, making it impossible to fine-tune
the size or position of a control. Follow these steps:
1. Change the GridSize property to 6, 6.
2. Change the ShowGrid property to True.
3. Click OK to save your changes and return to the Forms Designer. Notice that
grid dots now appear, as shown in Figure 6.2. If the dots don’t appear, you need
to close the tab in the designer and then double-click the OptionsForm.vb item
in the Solutions Explorer to force a refresh.
Try dragging the controls on your form or dragging their edges to size them. Notice
that you have more control over the placement with the finer grid. Try changing the
GridSize to a set of higher numbers, such as 25, 25, and see what happens. When
you’re finished experimenting, change the GridSize values to 4, 4.
FIGURE 6.2
Grids don’t have
to be visible to
be active.
122 HOUR 6: Building Forms: Advanced Techniques
An unfortunate side effect of a smaller grid is that the grid can become distracting.
Again, you’ll decide what you like best, but I generally turn off the grids on my forms.
In fact, I prefer the new Snap to Lines feature, discussed next.
The ShowGrid property determines only whether the grid is drawn, not whether it’s
active; whether a grid is active is determined by the form’s SnapToGrid property.
By the
Way
Using Snap Lines
A relatively new and useful feature is the Snap to Lines layout feature. Tell Visual
Basic 2010 to use Snap to Lines now by following these steps:
1. Choose Tools, Options to display the Options dialog box.
2. Click Windows Forms Designer to display the layout settings.
3. Change the LayoutMode property to SnapLines.
4. Turn off the grid by setting the ShowGrid property to False.
5. Click OK to save your settings.
Snap lines is a feature designed to help you create better interfaces faster by “snapping”
control edges to imaginary lines along the edges of other controls. The easiest
way to understand this is to try it. Follow these steps:
1. Drag your controls so that they are roughly in the position of Figure 6.3.
2. Click the ListBox to select it.
3. Click the white square that appears on the left edge of the control and drag it to
the left. As the edge nears vertical alignment with the button above it, a snap
line appears and the edge “snaps” to the line, as shown in Figure 6.4.
FIGURE 6.3
Start from this
layout.
Working with Controls 123
You’re free to continue dragging the edge, and as you do so, Visual Basic creates more
snap lines as you near vertical alignment with other controls. Controls also support
horizontal snap lines, and all snap lines also work when you drag a control. This
may seem like a small feature, but trust me when I say this is a great feature of
Visual Basic that will save you many tedious hours over time.
Selecting a Group of Controls
As your skills increase, you’ll find your forms becoming increasingly complex. Some
forms might contain dozens, or even hundreds, of controls. Visual Basic has a set of
features that makes it easy to align groups of controls.
By default, clicking a control on a form selects it while simultaneously deselecting any
controls that were previously selected. To perform actions on more than one control,
you need to select a group of controls. You can do this in one of two ways, the first of
which is to lasso the controls. To lasso a group of controls, you first click and drag the
mouse pointer anywhere on the form. As you drag, a rectangle is drawn on the form.
When you release the mouse button, all controls intersected by the rectangle become
selected. Note that you don’t have to completely surround a control with the lasso
(also called a marquee); you have to intersect only part of the control to select it. Try
this now: Click somewhere in the lower-left corner of the form, and drag the pointer
toward the upper-right of the form without releasing the mouse button. Intersect or
surround all controls except the OK button, as shown in Figure 6.5. When the rectangle
has surrounded or intersected all the controls, release the button, and the controls
are selected, as shown in Figure 6.6.
When a control is selected, it has a dotted border and a number of sizing handles
(squares located in the dotted border at the corners and midpoints of the control). Pay
careful attention to the sizing handles. The control with the white sizing handles is
the active control in the selected group. When you use Visual Basic’s tools to work on
a group of selected controls (such as the alignment and formatting tools), the values
of the active control are used. For example, if you were to align the left side of the
FIGURE 6.4
Snap lines make
it easy to align
the edges of
controls.
124 HOUR 6: Building Forms: Advanced Techniques
FIGURE 6.5
Click and drag to
create a selection
rectangle.
FIGURE 6.6
All selected controls
appear with
a dotted border
and sizing handles
(rectangles).
selected controls shown in Figure 6.6, each of the controls would have its Left property
value set to that of the active control (the control with the white handles). When
you use the lasso technique to select a group of controls, you really don’t have much
influence over which control Visual Basic makes the active control. In this example,
you want to align all controls to the button, so you have to use a different technique
to select the controls. Deselect all the controls now by clicking anywhere on the form
(just don’t click a control).
Not all sizing handles can be moved at all times. Before you set the Multiline
property of a text box to True, for example, Visual Basic doesn’t let you change
the height of the text box. Therefore, only the sizing handles at the left and right
edges can be moved, so they are white when the control is selected.
By the
Way
The second technique for selecting multiple controls is to use the Shift or Ctrl key
while clicking controls (either key can be used to the same effect). This method is
much like that used for selecting multiple files in Explorer. Follow these steps:
1. Click the bottom control (the list box) to select it. (When only one control is
selected, it’s considered the active control.)
Working with Controls 125
2. Hold down the Shift key and click the text box in the upper-left corner; the list
box and text box are now selected. The list box is the active control because it is
the first control you clicked when selecting this group. Again, when more than
one control is selected, the active control has its sizing handles set to white so
that you can identify it.
3. With the Shift key still pressed, click the button control (not the OK button) to
add it to the group of selected controls. All the controls should now be selected,
and the list box should be the active control.
Clicking a selected control while holding down the Shift key deselects the control. By the
Way
You can combine the two selection techniques when needed. For instance, you could
first lasso all the controls to select them. If you happen to select a control that you
don’t want in the group, simply hold down the Shift key and click that control to deselect
it.
If you must click the same control twice, such as to deselect and then reselect it,
do so s-l-o-w-l-y. If you click too fast, Visual Basic interprets your actions as a
double-click and creates a new event handler for the control.
By the
Way
Aligning Controls
Visual Basic includes a number of formatting tools you can use to design attractive
interfaces. You use the Layout toolbar, shown in Figure 6.7, to access most of these.
Display the Layout toolbar now by right-clicking a toolbar at the top of Visual Basic
and choosing Layout from the shortcut menu that appears. The Layout toolbar
includes options for aligning controls horizontally and vertically to the controls’
edges or centers.
Slowly move the mouse pointer from left to right over the buttons on this toolbar to
read their ToolTips. Notice that with this toolbar you can
. Align the left edge, middle, or right edge of selected controls.
. Align the top edge, middle, or bottom edge of selected controls.
FIGURE 6.7
The Layout toolbar
makes it
quick and easy
to align
controls.
126 HOUR 6: Building Forms: Advanced Techniques
. Make the selected controls the same width, height, or both.
. Make horizontal or vertical spacing between the selected controls nice and even.
. Move layering of the selected controls backward or forward.
. Set the tab order of the controls for fluid keyboard navigation.
The first item simply aligns the selected controls to the grid—not much fun there.
However, the remainder of the buttons are very useful. Remember that Visual Basic
uses the active control as its baseline when performing alignment. This is important.
Click the Align Tops button, and notice that the selected controls are now aligned
with the active control, as shown in Figure 6.8.
Making Controls the Same Size
In addition to aligning controls, you can make all selected controls the same size—
height, width, or both. To do this, use the Make Same Size button on the toolbar.
Make all your controls the same size now by clicking the Make the Same Size button.
This makes the selected controls the same size as the list box (rather large). Now try
this: In the Properties window, enter 75, 25 in the Size property, and press Tab to
commit the entry. Notice that your change affects all the selected controls. Having the
Properties window affect all selected controls like this makes it easy to quickly modify
a number of controls that need to share property values. I’ll talk about this in a little
more detail shortly.
Evenly Spacing a Group of Controls
As many a salesman has said, “...and that’s not all!” You can also make the spacing
between controls uniform, using the Layout toolbar. Try this now: Click the Make
Horizontal Spacing Equal button on the toolbar. All the controls are now evenly
FIGURE 6.8
The selected
control is used
as the baseline
when you align
groups of
selected controls.
Working with Controls 127
spaced. Next, click the Decrease Horizontal Spacing button on the toolbar a few times
and notice how the spacing between the controls decreases slightly with each click.
You can also increase the horizontal or vertical spacing or remove the spacing
between the controls, using buttons on the Layout toolbar. Save your project now by
clicking the Save All button on the toolbar.
Setting Property Values for a Group of Controls
The following is a technique that many experienced Visual Basic developers seem to
overlook: You can change a property value in the Properties window when multiple
controls are selected. This causes the corresponding property to change for all selected
controls.
Make sure that all three controls are still selected, and then display the Properties
window (if it’s not already displayed). When a group of controls is selected, the Properties
window appears with some modifications, as shown in Figure 6.9:
. No Name property is shown. This occurs because you’re not allowed to have two
controls with the same name, so Visual Basic doesn’t let you even try.
. Only properties shared by all controls are displayed. Because you have selected
controls of different types, only a small subset of common properties are available.
If you selected controls all of the same type, you’d see more properties
available.
. For properties where the values of the selected controls differ (such as the
Location property in this example), the value is left empty in the Properties
window.
Entering a value in a property changes the corresponding property for all selected
controls. To see how this works, change the BackColor property to a shade of yellow
and you’ll see that all controls have their BackColor set to yellow.
You won’t actually use the three controls you’ve been experimenting with so far in
this hour, so press the Delete key to delete all the selected controls.
FIGURE 6.9
You can view the
property values
of many controls
at once, with
some caveats.
128 HOUR 6: Building Forms: Advanced Techniques
Anchoring and Autosizing Controls
Some of my favorite evolutions to the forms engine in Visual Basic are the capability
to anchor controls to one or more edges of a form and the capability for controls to
size themselves appropriately when the user sizes a form. In the past, you had to use
a (usually cumbersome) third-party component or resort to writing code in the form
Resize event to get this behavior, but it’s an intrinsic capability of Visual Basic 2010’s
form engine.
The default behavior of all new controls is that controls are docked to the top and left
edges of their containers. What if you want a control to always appear in the upperright
or lower-left corner of a form? Now you’ll learn how to anchor controls so that
they adapt accordingly when the form is resized.
Follow these steps:
1. Double-click the form ViewerForm.vb in the Solutions Explorer window. This is
the form you’ll modify.
2. Press F5 to run the project.
3. Drag the lower-right corner of the form to make it bigger. Notice that the controls
don’t follow the edge of the form (see Figure 6.10).
4. Stop the running project by choosing Debug, Stop Debugging.
5. Click the Select Picture button to select it and, more importantly, deselect the form.
6. Hold down the Shift key and click the following additional buttons: Quit, Draw
Border, Options, ^, and v.
FIGURE 6.10
By default, controls
are
anchored to the
top-left corner of
the form.
Working with Controls 129
7. Click the Anchor property in the Properties window, and then click the dropdown
arrow that appears. You’ll see a drop-down box that’s unique to the
Anchor property, as shown in Figure 6.11.
The gray square in the center of the drop-down box represents the control whose
property you’re setting. The thin rectangles on the top, bottom, left, and right represent
the possible edges to which you can dock the control. If a rectangle is filled in,
the edge of the control facing that rectangle is docked to that edge of the form. Follow
these steps to see how the Anchor property works:
1. Click the rectangle on the left side of the control so that it’s no longer filled in,
and then click the rectangle to the right of the control so that it is filled in (see
Figure 6.12).
FIGURE 6.11
You use this
unique dropdown
box to set
a control’s
Anchor
property.
FIGURE 6.12
This setting
anchors the controls
to the top
and right edges
of the form.
130 HOUR 6: Building Forms: Advanced Techniques
2. Click any other property to close the drop-down box. The Anchor property
should now read Top, Right.
3. Press F5 to run the project, and then drag an edge of the form to make it larger.
Pretty interesting, huh? What Visual Basic has done is anchored the right edge of the
buttons to the right edge of the form, as shown in Figure 6.13. Really, anchoring
means keeping an edge of the control a constant, relative distance from an edge of
the form. It’s an unbelievably powerful tool for building interfaces.
Notice that the picture box and the coordinate labels still retain their original locations
when the form is resized. No problem—you can address that with the Anchor
property as well. Start by changing the anchoring of the X and Y labels by following
these steps (stop the running project if you haven’t already):
1. Click the X label to select it.
2. Hold down the Shift key, and click the Y label to select it.
3. Set the Anchor property the same as you did for the buttons—deselect the left
side and select the right side (refer to Figure 6.12).
4. Click any other property to close the Anchor drop-down box.
Now the picture box is a bit of a different beast from the other controls. You want the
top and left anchored the way they are now, but you want the right and bottom edge to
grow and shrink with the form. This is actually easy to accomplish. Follow these steps:
FIGURE 6.13
Anchoring is a
powerful feature
for creating
adaptable
forms.
Working with Controls 131
1. Click the picture box to select it.
2. Open the Anchor property and select all four anchor points. (All four rectangles
should be filled with solid gray, as shown in Figure 6.14.)
Now press F5 to run the project, and drag the lower right of the form to make it bigger.
Notice that now the picture box sizes itself to match the form size (see Figure
6.15). You’ll find this useful when viewing larger images.
Now that you know how to use the Anchor property, you can make forms that users
can resize with no code. One caveat: Depending on its Anchor setting, a control
might disappear if the form is shrunk quite small.
Creating a Tab Order
Tab order is something that is often (emphasis on often) overlooked by even seasoned
Visual Basic programmers. You’re probably familiar with tab order as a user,
FIGURE 6.14
This setting
anchors the control
relative to all
four sides of the
form.
FIGURE 6.15
Proper use of
the Anchor
property allows
you to build flexible
forms.
132 HOUR 6: Building Forms: Advanced Techniques
although you might not realize it. When you press Tab while on a form, the focus
moves from the current control to the next control in the tab order. This enables easy
keyboard navigation on forms. The tab order for controls on a form is determined by
the TabIndex properties of the controls. The control with the TabIndex value of 0 is
the first control that receives the focus when the form is first displayed. When you
press Tab, the control with a TabIndex of 1 receives the focus, and so on. When you
add a control to a form, Visual Basic assigns the next available TabIndex value to the
new control (it will be last in the tab order). Each control has a unique TabIndex
value, and TabIndex values are always traversed in ascending order.
If the tab order isn’t set correctly for a form, pressing Tab causes the focus to jump
from control to control in no apparent order. This is a great way to frustrate a user. In
the past, the only way to change the tab order for controls on a form was to manually
change the TabIndex values in the Properties window. For instance, to make a
control the first control in the tab order, you would change its TabIndex property to 0;
Visual Basic would then bump the values of all other controls accordingly. This was
often a painful process—believe me. Although it can be handy to set a TabIndex
property manually, such as when you want to insert a control into an existing tab
sequence, there is a much better way to set the tab order of forms.
Press F5 to run the project, and notice that the Select Picture button has the focus (it’s
highlighted by a blue rectangle). If you pressed Enter now, the button would be
“clicked” because it has the focus. Now press Tab, and the Quit button has the focus
because you added the Quit button to the form right after you added the Select Picture
button. Press Tab once more. Did you expect the Draw Border button to get the
focus? So would a user. Instead, the ^ button receives the focus because it was the
next control you added to the form. You’re about to fix that, so stop the project by
clicking Stop Debugging on the toolbar or close the running window.
Follow these steps to set the tab order of the form via the visual method of Visual Basic:
1. The last button on the Layout toolbar is the Tab Order button. Click it now, and
notice how Visual Basic superimposes a set of numbers over the controls, as
shown in Figure 6.16. The number on a control indicates its TabIndex property
value. Now it’s easy to see that the tab order is incorrect.
2. Click the Select Picture button. The background of the number changes from
blue to white to show that you selected the control. Had this control had a
TabIndex value other than 0, it would have been changed to 0 when you
clicked it.
3. Click the Quit button to designate it as the next button in the tab order.
4. Currently, the Draw Border button is fifth in the tab order. Click it, and the
number changes to 2.
Working with Controls 133
FIGURE 6.16
The numbers
over each control
indicate the
control’s
TabIndex.
5. Click the remaining controls in the following order: X label, Y label, Options
button, ^ button, and v button.
6. When you click the last button, all the numbers change back to a blue background;
the tab order is now set. Click the Tab Order button once more on the
Layout toolbar to take the designer out of Tab Order mode.
7. Press F5 to run the project again and you’ll see that pressing Tab now moves
the focus logically.
You can programmatically move the focus via the tab order by calling the
SelectNextControl() method of a control or form.
By the
Way
To remove a control from the tab sequence, set its TabStop property to False. When
a control’s TabStop property is set to False, users can still select the control with the
mouse, but they can’t enter the control by using the Tab key. You should still set the
TabIndex property to a logical value so that if the control receives the focus (such as
by being clicked), pressing Tab moves the focus to the next logical control.
Layering Controls
Tab order and visual alignment are key elements for effectively placing controls on
forms. However, these two elements address control placement in only two dimensions—
the x,y axis. Although it’s rare that you’ll need to do so, at times you might
134 HOUR 6: Building Forms: Advanced Techniques
need to have controls overlap. Whenever two controls overlap, whichever control was
added to the form most recently appears on top of the other. You can control the
ordering of controls by using the Bring to Front or Send to Back buttons found on the
right side of the Layout toolbar.
You can use code to move a control forward or backward by invoking the control’s
BringToFront() or SendToBack() methods.
Did you
Know?
Creating Topmost Nonmodal Windows
As you’re probably aware, when you click a window it usually comes to the foreground,
and all other windows are displayed behind it (unless it’s a modal window).
At times, you might want a window to stay on top of other windows, regardless of
whether it’s the current window (that is, it has the focus). An example of this is the
Find window in Visual Basic and other applications such as Word. Regardless of
which window has the focus, the Find form always appears floating over all other
windows. You create such a window by setting the form’s TopMost property to True.
It’s not exactly rocket science, but that’s the point: A simple property change or
method call is often all it takes to accomplish what might otherwise seem to be a difficult
task.
Creating Transparent Forms
A relatively new property of forms that I think is very cool is the Opacity property.
This property controls the form’s opaqueness as well as all controls on the form. The
default Opacity value of 100% means that the form and its controls are completely
opaque (solid), whereas a value of 0% creates a completely transparent form (no real
point in that). A value of 50%, then, creates a form that’s between solid and invisible,
as shown in Figure 6.17. Microsoft Outlook 2003 and newer make good use of opacity
in their alerts that pop up to tell you when you’ve received an email. The Opacity of
these alerts is cycled from 0 to 100, is left at 100 for a short time, and then cycles back
down to 0 as it disappears. You can do this in your program using a simple loop, as
discussed in Hour 14, “Looping for Efficiency.”
Creating Scrollable Forms
A scrollable form is one that can display scrollbars when its contents are larger than
the form’s physical size. Not only is this a great feature, but it’s also easy to implement
in your own applications.
Creating Scrollable Forms 135
FIGURE 6.17
Ghost forms!
Property Description
AutoScroll Determines whether scrollbars will ever appear on a
form.
AutoScrollMinSize The minimum size of the scroll region (area). If the
size of the form is adjusted so that the client area
of the form (the area of the form not counting
borders and title bar) is smaller than the
AutoScrollMinSize, scrollbars appear.
AutoScrollMargin Determines the margin given around controls during
scrolling. This essentially determines how far past
the edge of the outermost controls you can scroll.
Press F5 to run your project, and size the form smaller than it is by dragging the
lower-right corner toward the upper left. Notice that, although the controls adjust
themselves the best they can, some controls disappear from view as the form gets
smaller. The only way you can access these controls is to make the form bigger
again—unless you make this form a scrollable form.
A form’s scrolling behavior is determined by the following three properties:
136 HOUR 6: Building Forms: Advanced Techniques
Follow these steps:
1. If the project is still running, stop it.
2. Set the AutoScroll property of the ViewerForm.vb form to True.
3. Press F5 to run the project.
4. Drag the lower-right corner of the form toward the upper left to make the form
smaller. Notice that as you do so, a scrollbar appears on the right side of the
form, as shown in Figure 6.18. You can use the scrollbar to scroll the contents of
the form and access controls that would otherwise be unavailable.
Stop the project now, and save your work.
Creating MDI Forms
All the projects you’ve created so far have been single-document interface (SDI) projects.
In SDI programs, every form in the application is a peer of all other forms; no
intrinsic hierarchy exists between forms. Visual Basic also lets you create multipledocument
interface (MDI) programs. An MDI program contains one parent window
(also called a container) and one or more child windows. A classic example of an MDI
program is Adobe Photoshop. When you run Photoshop, a single parent window
appears. Within this parent window, you can open any number of documents, each
appearing in its own child window. In an MDI program, all child windows share the
same toolbar and menu bar, which appear on the parent window. One restriction of
child windows is that they can exist only within the confines of the parent window.
FIGURE 6.18
Without scrollbars,
it’s possible
to have
controls that
can’t be seen.
Creating MDI Forms 137
Figure 6.19 shows an example of Photoshop running with a number of child document
windows open.
MDI applications can have any number of normal windows (dialog boxes, for
example) in addition to child windows.
By the
Way
Now you’ll create a simple MDI project. Follow these steps:
1. Choose File, New Project to display the New Project dialog box (note how this is
a modal form). If asked, save your changes to the Picture Viewer project.
2. Enter the name MDI Example and click OK to create the project.
3. Right-click Form1.vb in the Solutions Explorer window and choose Rename
from the shortcut menu. Change the name of the form to MDIParentForm.vb.
Next, change the form’s Text property to MDI Parent, and change its
IsMdiContainer property to True. (If you don’t set the IsMdiContainer property
to True, this example won’t work.)
The first thing you’ll notice is that Visual Basic changed the client area to a
dark gray and gave it a sunken appearance. This is the standard appearance
for MDI parent windows; all visible child windows appear in this area.
FIGURE 6.19
Le Collage! MDI
applications consist
of a single
parent window
and one or more
child windows.
138 HOUR 6: Building Forms: Advanced Techniques
4. Create a new form by choosing Project, Add Windows Form. Name the form
Child1Form, and change its Text property to Child 1.
5. Add a third form to the project in the same way. Name it Child2Form, and set
its Text property to Child 2.
6. Click Save All on the toolbar, and name the project MDI Example.
7. Double-click MDIParentForm.vb in the Solution Explorer to show the parent
window in the designer.
8. Double-click the form to access its default event—the Load event. Enter the following
code:
Child1Form.MdiParent = Me
Child1Form.Show()
By now, you should know what the last statement does: It shows the form nonmodally.
What we’re interested in here is the first statement. It sets the form’s
MdiParent property to the current form, which is an MDI parent form because its
IsMdiContainer property is set to True. When the new form is displayed, it’s shown
as an MDI child.
Press F5 to run the project, and notice how the child form appears on the client area
of the parent form. If you size the parent form so that one or more child windows
can’t be displayed fully, a scrollbar appears (see Figure 6.20). If you were to remove
the statement that set the MdiParent property, the form would simply appear floating
over the parent form (because it wouldn’t be a child) and therefore wouldn’t be
bound by the confines of the parent.
FIGURE 6.20
Child forms
appear only
within the confines
of the parent
form.
Creating MDI Forms 139
Stop the project by choosing Debug, Stop Debugging, and follow these steps:
1. In the Solution Explorer, double-click the Child1Form.vb form to display it in
the designer.
2. Add a button to the form, and set the button’s properties as follows:
Any form can be a child form (except, of course, an MDI parent form). To make a
form a child form, set its MdiParent property to a form that’s defined as an MDI
container.
By the
Way
4. Press F5 to run the project. You’ll see the button on the child form, so go ahead
and click it. (If you don’t see the button, you might have mistakenly added it to
the second child form.) When you click the button, the second child form
appears, as shown in Figure 6.21. Notice how the new child form is also bound
by the constraints of the parent form.
The MDI parent form has an ActiveMdiChild property, which you can use to get a
reference to the currently active child window.
Did you
Know?
Property Value
Name btnShowChild2
Location 105, 100
Size 85, 23
Text Show Child 2
3. Double-click the button to access its Click event, and then add the following
code:
Child2Form.MdiParent = Me.MdiParent
Child2Form.Show()
This code shows the second child form. Note that differences exist between this
code and the code you entered earlier. You can’t set the second child’s
MdiParent property to Me because Me refers to the current form (Child1Form,
which is not an MDI container). However, you know that Me.MdiParent references
a child’s parent form because this is precisely the property you set to make
the form a child in the first place. Therefore, you can simply pass the parent of
the first child to the second child, and they’ll both be children of the same form.
140 HOUR 6: Building Forms: Advanced Techniques
FIGURE 6.21
Child forms are
peers with one
another.
To make the parent form larger when the project is first run, you would set the
form’s Size.Height and Size.Width properties either at design time or at runtime
in the form’s Load event.
By the
Way
One thing to keep in mind about forms is that you can create as many instances of a
form as you want. Managing multiple instances of the same form gets tricky, however,
and is beyond the scope of this book.
Setting the Startup Form
The Startup object in a Windows Application project is, by default, the first form
added to the project. This also happens to be the form that Visual Basic creates automatically
when you create a new Windows Application project.
Every Windows Forms project must have a Startup form as the entry point to the program.
You change the Startup form by right-clicking the project name in the Solution
Explorer and choosing Properties. The Startup form property appears on the first
property page that appears, as shown in Figure 6.22.
If the Startup object property is set to show a child window, you might not get the
behavior you expect when the project starts. The designated form would appear, but
it wouldn’t be a child, because no code would execute to set the form’s MdiParent
property to a valid MDI parent form.
Setting the Startup Form 141
FIGURE 6.22
The application’s
entry point is
determined by
the Startup
form property.
If MDI forms still confuse you, don’t worry. Most of the applications you’ll write as a
new Visual Basic programmer will be SDI programs. As you become more familiar
with creating Visual Basic projects in general, start experimenting with MDI projects.
Remember, you don’t have to make a program an MDI program simply because you
can; make an MDI program if the requirements of the project dictate that you do so.
Summary
Understanding forms is critical because forms are the dynamic canvases on which
you build your user interface. If you don’t know how to work with forms, your entire
application will suffer. Many things about working with forms go beyond simply setting
properties, especially as you begin to think about the end user. As your experience
grows, you’ll get into the groove of form design, and things will become second
nature to you.
In this hour, you learned how to do some interesting things, such as creating transparent
forms, as well as some high-end techniques, such as building an MDI application.
You learned how to create scrolling forms—an interface element that shouldn’t
be overlooked. You also spent a lot of time working with controls on forms, which is
important because the primary function of a form is as a place to host controls. In
the next two hours, you’ll learn the details of many of Visual Basic’s powerful controls
that will become important weapons in your vast development arsenal.
142 HOUR 6: Building Forms: Advanced Techniques
Q&A
Q. Do I need to worry about the anchoring and scrolling capabilities of every
form I create?
A. Absolutely not. The majority of forms in most applications are dialog boxes. A
dialog box is a modal form used to gather data from the user. A dialog box is
usually of a fixed size, which means that its border style is set to a style that
can’t be sized. With a fixed-size form, you don’t need to worry about anchoring
or scrolling.
Q. How do I know whether a project is a candidate for an MDI interface?
A. If the program will open many instances of the same type of form, that project
is a candidate for an MDI interface. For example, if you’re creating an imageediting
program and the intent is to enable the user to open many images at
once, MDI makes sense. Also, if you’ll have many forms that will share a common
toolbar and menu, you might want to consider MDI.
Workshop
Quiz
1. True or false: The first control selected in a series is always made the active
control.
2. How many ways are there to add a control to a form from the toolbox?
3. If you double-click a tool in the toolbox, where on the form is it placed?
4. Which property fixes an edge of a control to an edge of a form?
5. What do you change to hide the grid on a form?
6. Which toolbar contains the functions for spacing and aligning controls?
7. Which property do you set to make a form an MDI parent?
Answers
1. True
2. There are three primary methods: Double-click a tool in the toolbox, drag a tool
from the toolbox, and click a tool in the toolbox and then draw it on a form.
Workshop 143
3. The control is placed over the currently selected control, or in the upper-left
corner if no control is selected.
4. The Anchor property
5. The ShowGrid property, found in the Options dialog box
6. The Layout toolbar
7. You set the IsMdiContainer property to True to make a form an MDI parent.
Exercises
1. Create a new Windows Application, and add a button to the middle of the
form. Experiment with different values for the button’s Anchor property, running
the project in between property changes.
2. Modify the MDI Example project in this hour so that the first child that
appears is Child2Form, which in turn shows Child1Form.
This page intentionally left blank
Displaying Static Text with the Label Control 145
HOUR 7
Working with Traditional
Controls
What You’ll Learn in This Hour:
. Displaying static text with the Label control
. Allowing users to enter text using a text box
. Creating password fields
. Working with buttons
. Using panels, group boxes, check boxes, and option buttons
. Displaying lists with list boxes and combo boxes
The preceding two hours described in considerable detail how to work with forms.
Forms are the foundation of a user interface but are pretty much useless by themselves.
To create a functional interface, you need to use controls. Controls are the various
widgets and doodads on a form with which users interact. Dozens of different
types of controls exist, from the simple Label control, used to display static text, to
the more complicated Tree View control, used to present trees of data like those
found in Explorer. In this hour, I’ll introduce you to the most common (and simple)
controls, which I call traditional controls. In Hour 8, “Using Advanced Controls,”
you’ll learn about the more advanced controls that you can use to create
professional-level interfaces.
Displaying Static Text with the Label
Control
Label controls are used to display static text to the user. By static, I mean that the
user can’t change the text directly (but you can change the text with code). Label
controls are among the most commonly used controls, and, fortunately, they’re also
among the easiest. Labels are most often used to provide descriptive text for other
146 HOUR 7: Working with Traditional Controls
controls such as text boxes. Labels are also great for providing status-type information
to a user, as well as for providing general instructions on a form.
You’ll build on the Picture Viewer project from Hour 6, “Building Forms: Advanced
Techniques,” for most of this hour. Although you’ll add the controls to the interface,
you won’t make them functional until you progress to Part III, “Making Things Happen:
Programming.”
Start by following these steps:
1. Open the Picture Viewer you worked on in Hour 6.
2. Double-click OptionsForm.vb in the Solution Explorer window to display the
Options form in the designer.
3. Add a new Label control to the form by double-clicking the Label item in the
toolbox. The primary property of the Label control is the Text property, which
determines the text displayed to the user. When a Label control is first added
to a form, the Text property is set to the control’s name. This isn’t very useful.
Set the properties of the new Label control as follows:
Property Value
Name lblUserName
Location 40, 41
Text User Name:
Notice how the label resizes automatically to fit your text. To create a multiline label,
you would click in the Text property to display a drop-down arrow and then click the
arrow to access a text editor, as shown in Figure 7.1. You could then enter text and
separate the lines by pressing Enter. In most cases, it’s best to place label text on a
single line, but it’s nice to have the option.
Allowing Users to Enter Text Using a
Text Box
A Label control is usually the best control for displaying text that a user can’t
change. However, when you need to allow users to enter or edit text, the text box is
the tool for the job. If you’ve ever typed information on a form, you’ve almost cer-
Allowing Users to Enter Text Using a Text Box 147
FIGURE 7.1
Multiline labels
are created with
this text editor.
tainly used a text box. Add a new text box to your form now by double-clicking the
TextBox item in the toolbox. Set the text box’s properties as follows:
Your form should now look like Figure 7.2.
Property Value
Name txtUserName
Location 105, 38
Size 139, 20
FIGURE 7.2
Labels and text
boxes work well
together.
Although you’ll leave the Text property of a text box empty 99% of the time, certain
aspects of the text box are easier to understand when it contains text. For now, set
the text box’s Text property to This is sample text. Remember to press Enter or
Tab to commit your property change.
148 HOUR 7: Working with Traditional Controls
Specifying Text Alignment
Both the Text Box and Label controls have a TextAlign property (as do many
other controls). The TextAlign property determines the alignment of the text within
the control, much like the justification setting in a word processor. You can select
from Left, Center, and Right.
Follow these steps to see how the TextAlign property works:
1. Change the TextAlign property of the text box to Right, and see how the text
becomes right-aligned within the text box.
2. Change TextAlign to Center to see what center alignment looks like. As you
can see, this property is pretty straightforward.
3. Change the TextAlign property back to Left before continuing.
Creating a Multiline Text Box
In Hour 6, I talked about the sizing handles of a selected control. I mentioned how
handles that can be sized are filled with white, and handles that are locked appear
with a gray center. Notice how only the left and right edges of the text box have
white sizing handles. This means that you can adjust only the left and right edges of
the control (you can alter only the width, not the height). This text box is defined as
a single-line text box, meaning that it displays only one line of text. What would be
the point of a really tall text box that showed only a single line of text?
To allow a text box to display multiple lines of text, set its Multiline property to
True. Set the Multiline property of your text box to True now, and notice how all
the sizing handles become white. Although you could set this using the Properties
window, there is a nifty shortcut for setting the MultiLine property of a text box.
Select the text box, and then click the little square with the arrow that appears above
the text box (refer to Figure 7.2). This displays a simple shortcut menu showing the
MultiLine property value. Click the check box next to the value, and then click off
the menu to close it. Most controls have such a shortcut menu, but the contents
depend on the type of control selected. Get used to opening these shortcut menus
when you see the little box with the arrow so that you can become familiar with the
properties each control makes available in its shortcuts.
Change the Text property of the text box to This is sample text. A multiline text
box will wrap its contents as necessary. Press Enter or Tab to commit the property
change. Figure 7.3 shows how the text box displays only part of what you entered
Allowing Users to Enter Text Using a Text Box 149
because the control simply isn’t big enough to show all the text. Change the Size
property to 139, 52, and you’ll then see the entire contents of the text box, as shown
in Figure 7.4.
There will be times when you won’t want a user to be able to interact with a control.
For example, you might implement a security model in an application, and if the
user doesn’t have the necessary privileges, you might prevent him or her from altering
data. The Enabled property, which almost every control has, determines whether
the user can interact with the control. Change the Enabled property of the text box
to False, press F5 to run the project, and click Options to show the Options form.
Although no noticeable change occurs in the control in Design view, there’s a big
change to the control at runtime: The text appears in gray rather than black, and
the text box doesn’t accept the focus or allow you to change the text (see Figure 7.5).
FIGURE 7.3
A text box might
contain more
text than it can
display.
FIGURE 7.4
A multiline text
box can be sized
as large as necessary.
150 HOUR 7: Working with Traditional Controls
Stop the project now by choosing Debug, Stop Debugging, and then change the control’s
Enabled property back to True.
Adding Scrollbars
Even though you can size a multiline text box, there will still be times when the contents
of the control are more than can be displayed. If you believe this is a possibility
for a text box you’re adding to a form, give the text box scrollbars by changing the
ScrollBars property from None to Vertical, Horizontal, or Both.
For a text box to display scrollbars, its Multiline property must be set to True.
Also, if you set the ScrollBars property to Both, the horizontal scrollbar won’t
appear unless you also set the WordWrap property to False. If you set WordWrap
equal to True, text will always wrap to fit the control, so there will never be any
text off to the right of the text box, and there will be no need for a horizontal
scrollbar.
By the
Way
Change the ScrollBars property of your text box to Vertical, and notice how a
scrollbar appears in the text box (see Figure 7.6).
If you set a text box’s AcceptsReturn property to True, the user can press Enter
to create a new line in the text box. When the AcceptsTabs property is set to
True, the user can press Tab within the control to create columns (rather than
moving the focus to the next control).
By the
Way
FIGURE 7.5
You can’t interact
with a text
box whose
Enabled property
is set to
False.
Allowing Users to Enter Text Using a Text Box 151
FIGURE 7.6
If a text box
might contain a
lot of text, give it
a scrollbar.
Limiting the Number of Characters a User Can Enter
You can limit how many characters a user can type into a text box by using the
MaxLength property. All new text boxes are given the default value of 32767 for
MaxLength, but you can change this as needed. To see how this works, follow these steps:
1. Change the text box’s properties as follows:
Property Value
Text Make empty (This means that you should clear out the value.)
MaxLength 10
Multiline False
ScrollBars None
2. Press F5 to run the project.
3. Click the Options button to display the Options form.
4. Enter the following text into the new text box: So you run and you run. Notice
that you can’t enter more than 10 characters of text; all you’re allowed to enter
is So you run. The text box allows only 10 characters, whether you use the
keyboard or a Paste operation. The MaxLength property is most often used
when the text box’s content is to be written to a database, in which field sizes
152 HOUR 7: Working with Traditional Controls
are usually restricted. (Using a database is discussed in Hour 21, “Working with
a Database.”)
5. Stop the project, and change the MaxLength property of the text box to 0, which
effectively means that no maximum is defined.
Now would be a good time to save your work.
Creating Password Fields
You’ve probably used a password field: a text box that displays an asterisk for each
character entered. You can make any text box a password field by assigning a character
to its PasswordChar field. Select the PasswordChar property of the text box and
enter an asterisk (*) for the property value. Run the project once more, and display
the Options form. Next, enter text into the text box. An asterisk is displayed for each
character you enter, as shown in Figure 7.7. Although the user doesn’t see the actual
text contained in the text box, referencing the Text property in code always returns
the true text.
A text box displays password characters only if its Multiline property is set to
False.
By the
Way
Stop the project by choosing Debug, Stop Debugging. Delete the asterisk from the
PasswordChar field, and then save the project by clicking Save All on the toolbar.
FIGURE 7.7
A password field
displays its
password character
for all
entered text.
Allowing Users to Enter Text Using a Text Box 153
Understanding the Text Box’s Common Events
You’ll rarely use a label’s events, but you’ll probably use text box events quite a bit.
The text box supports many different events; Table 7.1 lists the ones you’re most
likely to use regularly.
TABLE 7.1 Commonly Used Events of the Text Box Control
Event Description
TextChanged Occurs every time the user presses a key or pastes text into the
text box. Use this event to deal with specific keypresses (such as
to capture specific keys) or when you need to perform an action
whenever the contents change.
Click Occurs when the user clicks the text box. Use this event to
capture clicks when you don’t care about the coordinates of the
mouse pointer.
MouseDown Occurs when the user first presses a mouse button over the text
box. This event is often used in conjunction with the MouseUp
event.
MouseUp Occurs when the user releases a mouse button over the text box.
Use MouseDown and MouseUp when you need more functionality
than provided by the Click event.
MouseMove Occurs when the user moves the mouse pointer over the text box.
Use this event to perform actions based on the cursor’s
movement.
154 HOUR 7: Working with Traditional Controls
Creating Buttons
Every dialog box that Windows displays has at least one button. Buttons enable a
user to invoke a function with a click of the mouse.
The form already has an OK button. Typically, an OK button accepts the user’s values
and closes the form. Later in this book, you’ll make your OK button do just that.
When you have an OK button, it’s also a good idea to create a Cancel button, which
unloads the form but doesn’t save the user’s values.
Add a new button to the form by double-clicking the Button item in the toolbox. Set
the button’s properties as follows:
You can programmatically trigger a button’s Click event, just as though a user
clicked it, by calling the button’s PerformClick method.
Did you
Know?
Accept and Cancel Buttons
When creating dialog boxes, it’s common to assign one button as the default button
(called the Accept button). If a form has an Accept button, that button’s Click event
is fired when the user presses Enter, regardless of which control has the focus. This is
great for dialog boxes in which the user enters some text and presses Enter to commit
the data and close the form.
Property Value
Name btnCancel
Location 305, 38
Text Cancel
There’s no point in having a button that doesn’t do anything, so double-click the
button now to access its Click event, and then add the following statement:
Me.Close()
Recall from Hour 5, “Building Forms: The Basics,” that this statement closes the current
form. Right now, the Cancel button does the same thing as the OK button, but
you’ll change that soon.
Creating Buttons 155
Follow these steps to designate the OK button as the Accept button:
1. Double-click OptionsForm.vb in the Solution Explorer window to show the form
in the designer once more.
2. Click the form to display its properties in the Properties window.
3. Click the form’s AcceptButton property in the Properties window; a drop-down
arrow appears. Click the arrow, and choose the button btnOK from the list.
Notice that the button now has a blue border on the form, indicating that it is
the default button for the form (see Figure 7.8).
4. Press F5 to run the project, and then click Options to display the Options form.
5. Click in the text box to make sure that it has the focus, and then press Enter;
the form closes. Again, pressing Enter on a form that has a designated Accept
button causes that button’s Click event to fire the same as if the user clicked it
with the mouse, regardless of which control has the focus. Actually, there is one
exception. If the control with the focus is a multiline text box, pressing Enter
creates a new line in the text box and doesn’t cause the Accept button’s Click
event to fire.
Generally, when you create an Accept button for a form, you should also create a
Cancel button. A Cancel button fires its Click event when the user presses the Esc key
FIGURE 7.8
The Accept button
appears blue
and has a
thicker border.
156 HOUR 7: Working with Traditional Controls
(as opposed to the Enter key), regardless of which control has the focus. Generally,
you place code in a Cancel button to shut down the form without committing any
changes the user made. Make your Cancel button an official Cancel button by following
these steps:
1. Stop the running project.
2. Change the form’s CancelButton property to btnCancel.
Use the following hints when deciding what buttons to assign as a form’s Accept and
Cancel buttons:
. If a form has an OK or Close button, that button probably should be assigned
as the AcceptButton.
. If a form has both an OK and Cancel button, assign the OK button as the
AcceptButton and the Cancel button as the CancelButton (yeah, this is pretty
obvious, but it’s often overlooked).
. If a form has a single Close or OK button, assign it to both the form’s
AcceptButton and CancelButton properties.
. If the form has a Cancel button, assign it to the form’s CancelButton property.
Presenting Yes/No Options Using Check Boxes
A check box is used to display true/false and yes/no values on a form. You’ve probably
run into many check boxes as you’ve worked with different Windows applications.
Clicking the check box control toggles it between checked and unchecked
(true/false, yes/no, and so on).
Add a new check box to the Options form now, and set its properties as follows:
Property Value
Name chkPromptOnExit
Location 105, 79
Text Prompt to confirm on exit
The CheckState property of the check box determines whether the check box is
checked. Try changing the value of this property, and watch the effect on the form.
Notice that you can set the check box’s CheckState to Indeterminate, which shows
a big square in the control. You won’t often need to use this, but it’s good to know the
feature is available. Be sure to set the CheckState to Unchecked before continuing.
Creating Containers and Groups of Option Buttons 157
Your form should now look like Figure 7.9.
Creating Containers and Groups of
Option Buttons
In this section, you’ll learn how to create containers for groups of controls, using panels
and group boxes. You’ll also learn how to use the Option Button control in conjunction
with these container controls to present multiple choices to a user.
Using Panels and Group Boxes
Controls can be placed on a form because the form is a container object—an object
that can host controls. A form isn’t the only type of container, however. Some controls
act as containers as well, and a container can host one or more other containers. The
Panel and Group Box controls are both container controls that serve a similar purpose,
yet each is more suited to a particular application.
The Group Box is a container control with properties that let you create a border,
called a frame, and a caption. Add a new group box to your form now by doubleclicking
the GroupBox item in the toolbox (you’ll find it in the Containers control
category). When you create a new group box, it has a border by default, and its caption
is set to the name of the control.
Try clicking in the center of the group box and dragging it around as you would
another type of control. You can’t. Think of the group box as a mini form—you can’t
click and drag a form to move it around. Clicking and dragging a group box lassos
any controls placed on the group box—the same behavior you experience on a form.
FIGURE 7.9
Use the check
box to indicate a
true/false or
yes/no state.
158 HOUR 7: Working with Traditional Controls
To drag a group box, click and drag the little image with the four arrows on it, as
shown in Figure 7.10.
Set the properties of the group box as follows:
Your group box should now look like the one shown in Figure 7.11.
For the most part, the Panel control is a slimmed-down version of the Group Box
control, so I won’t discuss it in depth. If you need a basic container control without
the additional features offered by the Group Box control (such as a border
and caption), use the Panel control. The primary exception to this is that the
panel offers scrolling capabilities just like those found on forms, which group
boxes do not support.
By the
Way
Property Value
Name grpDefaultBackcolor
Location 105, 112
Size 200, 72
Text Default Picture Background Color
FIGURE 7.10
Click and drag
this box to move
a group box.
FIGURE 7.11
A group box acts
like a form within
a form.
The Group Box is a fairly straightforward control. Other than defining a border and
displaying a caption, the purpose of a group box is to provide a container for other
controls. The next section demonstrates the benefits of using a group box as a container.
Creating Containers and Groups of Option Buttons 159
Working with Radio Buttons
Check boxes are excellent controls for displaying true/false and yes/no values. However,
check boxes work independently of one another. If you have five check boxes on
a form, each one can be checked or unchecked—in any combination. Radio buttons,
on the other hand, are mutually exclusive to the container on which they’re placed.
This means that only one radio button per container can be selected at a time. Selecting
one radio button automatically deselects any other radio buttons on the same
container. Radio buttons are used to offer a selection of items when the user is
allowed to select only one item. To better see how mutual exclusivity works, you’ll create
a small group of radio buttons for your Options form.
You can perform any of the following actions to place a control on a group box:
. Draw the control directly on the group box.
. Drop the control on the group box.
. Add the control to the form, cut the control from the form, select the group box,
and paste the control on the group box.
You’ll use the second method: dropping a new control directly on the group box. Follow
these steps:
1. Click the RadioButton item in the toolbox, and drag it to the group box.
2. Release the mouse button when you’re over the group box.
3. Move the radio button around by clicking and dragging it. Don’t drag the radio
button off the container, or it will be moved to the new container or form over
which it is placed when you release the mouse button.
Set the properties of the radio button as follows:
Property Value
Name optBackgroundDefault
Location 14, 19
Text Default Gray
Note that the Location property always refers to the container form’s upper-left corner.
If the control is on a group box, the location is relative to the upper-left corner of
the group box. Now you’ll copy this radio button and paste a copy of the control on
the group box:
160 HOUR 7: Working with Traditional Controls
1. Right-click the radio button, and choose Copy from its context menu.
2. Click the group box to select it.
3. Right-click the group box, and choose Paste from its context menu to create a
new radio button. Set the properties of the radio button as follows:
Now that you have your two radio buttons, as shown in Figure 7.12, run the project
by pressing F5.
Click the Options button to display your Options form, and take a look at the radio
buttons. The second radio button is selected, so click the first radio button (Default
Gray). Notice how the second radio button becomes deselected automatically (its
Checked property is set to False). Two radio buttons are sufficient to demonstrate
mutual exclusivity, but be aware that you could add as many radio buttons to the
group box as you want to and the behavior would be the same.
The important thing to remember is that mutual exclusivity is shared only by radio
buttons placed on the same container. To create radio buttons that behave independently
of one another, you would need to create a second set on another container. You
could easily create a new group box (or panel, for that matter) and place the second
set of radio buttons on the new container. The two sets of radio buttons would behave
Property Value
Name optBackgroundWhite
Checked True
Location 14, 42
Text White
FIGURE 7.12
Radio buttons
restrict a user to
selecting a single
item.
Displaying a List with the List Box 161
independently of one another, but mutual exclusivity would still exist among the buttons
within each set.
Stop the running project, change the Checked property of the
optBackgroundDefault radio button to True, and save your work.
Displaying a List with the List Box
A list box is used to present a list of items to a user. You can add items to, and remove
items from, the list at any time with very little Visual Basic code. In addition, you can
set up a list box so that a user can select only a single item or multiple items. When a
list box contains more items than it can show because of the control’s size, a scrollbar
appears automatically.
The cousin of the list box is the combo box, which looks like a text box with a
down-arrow button on its right side. Clicking a combo box’s button causes the
control to display a drop-down list box. Working with the list of a combo box is
pretty much identical to working with a list box. Therefore, I’ll discuss the details
of list manipulation in this section and then discuss the features specific to the
combo box in the next section.
By the
Way
You won’t add a list box or combo box to your Picture Viewer project at this time, so
follow these steps to create a new project:
1. Create a new Windows Forms Application project titled Lists.
2. Rename the default form ListsForm.vb, and set its Text property to Lists
Example.
3. Add a new List Box control to the form by double-clicking the ListBox item in
the toolbox, and then set the list box’s properties as follows:
Property Value
Name lstChemicalEchoSongs
Location 64, 32
Size 160, 121
Every item in a list box is a member of the list box’s Items collection. You work with
items, including adding and removing items, using the Items collection. You’ll most
often manipulate the Items collection using code (as I’ll show you a little later in this
hour), but you can also work with the collection at design time by using the Properties
window.
162 HOUR 7: Working with Traditional Controls
Manipulating Items at Design Time
The Items collection is available as a property of the list box. Locate the Items property
in the Properties window and click it to select it. The familiar button with three
dots appears, indicating that you can do advanced things with this property. Click
the button now to show the String Collection Editor. To add items to the collection,
simply enter the items into the text box—one item to a line.
Enter the following items:
. Persian Wind
. Portal
. Dark and Stormy Night
. Cadence of Madness
. Lift Off
. Reentry
When you’re finished, your screen should look like that shown in Figure 7.13. Click
OK to commit your entries and close the window. Notice that the list box contains the
items you entered.
Manipulating Items at Runtime
In Hour 3, “Understanding Objects and Collections,” you learned about objects, properties,
methods, and collections. All this knowledge comes into play when you manipulate
lists at runtime. The Items property of a list box (and a combo box, for that
matter) is an object property that returns a collection. Collections in many ways are
FIGURE 7.13
Use this dialog
box to manipulate
an Items
collection at
design time.
Displaying a List with the List Box 163
like objects—they have properties and methods. To manipulate list items, you manipulate
the Items collection.
A list can contain duplicate values, as you’ll see in this example. Visual Basic therefore
needs a mechanism other than an item’s text to treat each item in a list as
unique. You do this by assigning each item in an Items collection a unique index.
The first item in the list has an index of 0, the second an index of 1, and so on. The
index is the ordinal position of an item relative to the first item in the Items collection—
not the first item visible in the list.
Adding Items to a List
You add new items to the Items collection by using the Add() method of the Items
collection. Now you’ll create a button that adds a song to the list. Add a new button
to the form, and set its properties as follows:
Double-click the button to access its Click event, and add the following code:
lstChemicalEchoSongs.Items.Add(“Orbit”)
Notice that the Add() method accepts a string argument—the text to add to the list.
Unlike items added at design time, items added through code aren’t preserved
when the program ends.
By the
Way
Press F5 to run the project, and click the button. When you do, the new song is added
to the bottom of the list. Clicking the button a second time adds another item to the
list with the same album name. The list box doesn’t care whether the item already
Property Value
Name btnAddSong
Location 96, 159
Size 100, 23
Text Add a Song
164 HOUR 7: Working with Traditional Controls
exists in the list; each call to the Add() method of the Items collection adds a new
item to the list.
The Add() method of the Items collection can be called as a function. In that case it
returns the index (the ordinal position of the newly added item in the underlying collection),
as in the following:
Dim intIndex As Integer
intIndex = lstChemicalEchoSongs.Items.Add(“Orbit”)
Knowing the index of an item can be useful, as you will see.
Stop the running project, and save your work before continuing.
To add an item to an Items collection at a specific location in the list, use the
Insert() method. The Insert() method accepts an index in addition to text.
Remember, the first item in the list has an index of 0, so to add an item at the
top of the list you could use a statement such as
lstChemicalEchoSongs.Items.Insert(0,”Orbit”).
Did you
Know?
Removing Items from a List
Removing an individual item from a list is as easy as adding an item. It requires only
a single method call: a call to the Remove() method of the Items collection. The
Remove() method accepts a string, which is the text of the item to remove. Now you’ll
create a button that removes an item from the list.
Display the form designer, and create a new button on the form. Set the button’s
properties as follows:
Double-click the new button to access its Click event, and enter the following
statement:
lstChemicalEchoSongs.Items.Remove(“Orbit”)
The Remove() method tells Visual Basic to search the Items collection, starting at the
first item (index = 0), and to remove the first item found that matches the specified
Property Value
Name btnRemoveSong
Location 96, 188
Size 100, 23
Text Remove Song
Displaying a List with the List Box 165
text. Remember, you can have multiple items with the same text. The Remove()
method removes only the first occurrence. After the text is found and removed, Visual
Basic stops looking.
Press F5 to run the project again. Click the Add a Song button a few times to add
Orbit to the list, as shown in Figure 7.14. Next, click the Remove a Song button, and
notice how Visual Basic finds and removes one instance of the specified song.
To remove an item at a specific index, use the RemoveAt() method. For example,
to remove the first item in the list, you would use the following statement:
lstChemicalEchoSongs.Items.RemoveAt(0). Be aware that this code will throw
an exception (an error) if there are no items in the list when it is called.
Did you
Know?
Stop the running project, and save your work.
Clearing a List
To clear the contents of a list box, use the Clear() method. You’ll add a button to the
form that, when clicked, clears the list. Add a new button to the form, and set the button’s
properties as follows:
FIGURE 7.14
The list box can
contain duplicate
entries, but each
entry is a unique
item in the
Items
collection.
Property Value
Name btnClearList
Location 96, 217
Size 100, 23
Text Clear List
166 HOUR 7: Working with Traditional Controls
Double-click the new button to access its Click event, and enter the following
statement:
lstChemicalEchoSongs.Items.Clear()
Press F5 to run the project, and then click the Clear List button. The Clear() method
doesn’t care whether an item was added at design time or runtime; Clear() always
removes all items from the list. Stop the project, and again save your work.
Remember that the Add(), Insert(), Remove(), RemoveAt(), and Clear()
methods are all methods of the Items collection, not of the list box itself. If you
forget that these are members of the Items collection, you might be confused
when you don’t find them when you enter a period after typing a list box’s name in
code.
Did you
Know?
Retrieving Information About the Selected Item in a List
Two properties provide information about the selected item: SelectedItem and
SelectedIndex. It’s important to note that these are properties of the list box itself,
not of the Items collection of a list box. The SelectedItem method returns the text of
the currently selected item. If no item is selected, the method returns an empty string.
It is sometimes desirable to know the index of the selected item. You can obtain this
by using the SelectedIndex property of the list box. As you know, the first item in a
list has an index of 0. If no item is selected, SelectedIndex returns –1, which is never
a valid index for an item.
Now you’ll add a button to the form that, when clicked, displays the selected item’s
text and index in a message box. First, stop the running project, and change the
form’s Size.Height property to 320 to accommodate one more button. As you build
your interfaces, you’ll often have to make small tweaks like this because it’s nearly
impossible to anticipate everything ahead of time.
Add a new button to the form, and set its properties as follows:
Property Value
Name btnShowItem
Location 96, 246
Size 100, 23
Text Show Selected
Displaying a List with the List Box 167
Double-click the new button to access its Click event, and enter the following statement
(be sure to press Enter at the end of the first line):
MessageBox.Show(“You selected “ & lstChemicalEchoSongs.SelectedItem & _
“, which has an index of “ & lstChemicalEchoSongs.SelectedIndex)
MessageBox.Show() is a Visual Basic function used to show a message to the user.
You’ll learn about MessageBox.Show() in detail in Hour 17, “Interacting with Users.”
Press F5 to run the project, and click the Show Selected button. Notice that because
nothing is selected, the message box doesn’t read quite right, and it says that the
selected index is –1 (which indicates that nothing is selected). Click an item in the list
to select it, and then click Show Selected again. This time, you see the text of the
selected item and its index in the message box, as shown in Figure 7.15. Stop the running
project, and save your work.
You can set up a list box to allow multiple items to be selected at once. To do
this, you change the SelectionMode property of the list box to MultiSimple
(clicking an item toggles its selected state) or MultiExtended (you have to hold
down Ctrl or Shift to select multiple items). To determine which items are
selected in a multiselection list box, use the list box’s SelectedItems collection.
By the
Way
Sorting a List
List boxes and combo boxes have a Sorted property. This property is set to False
when a control is first created. Changing this property value to True causes Visual
FIGURE 7.15
The
SelectedItem
and
SelectedIndex
properties make
it easy to determine
which item
in a list is
selected.
168 HOUR 7: Working with Traditional Controls
Basic to sort the contents of the list alphabetically. When the contents of a list are
sorted, the index of each item in the Items collection is changed; therefore, you can’t
use an index value obtained prior to setting Sorted to True.
Sorted is a property, not a method. Realize that you don’t have to call Sorted to sort
the contents of a list; Visual Basic enforces a sort order as long as the Sorted property
is set to True. This means that all items added via the Add() method or the
Insert() method are automatically inserted into the proper sorted location, in contrast
to being inserted at the end of the list or in a specific location.
Stop the running project, and save your work.
Creating Drop-Down Lists Using the
Combo Box
List boxes are great, but they have two shortcomings. First, they take up quite a bit of
space. Second, users can’t enter their own values; they have to select from the items
in the list. If you need to conserve space, or if you want to enable a user to enter a
value that might not exist in the list, use the Combo Box control.
Combo boxes have an Items collection that behaves exactly like that of the List
Box control (refer to the preceding section for information on manipulating lists).
Here I’ll show you the basics of how a combo box works.
Add a new combo box to the form by double-clicking the ComboBox item in the toolbox.
Set the combo box’s properties as follows:
Property Value
Name cboColors
Location 64, 5
Size 160, 21
Text Leave blank
The first thing you should note is that the combo box has a Text property, whereas
the list box doesn’t. This works the same as the Text property of a text box. When
the user selects an item from the drop-down list, the value of the selected item is
placed in the Text property of the text box. The default behavior of a combo box is
to allow the user to enter any text in the text box portion of the control—even if the
text doesn’t exist in the list. I’ll show you how to change this behavior shortly.
Creating Drop-Down Lists Using the Combo Box 169
Select the Items property of the combo box in the Properties window, and click the
button that appears. Add the following items to the String Collection Editor, and click
OK to commit your entries:
. Black
. Blue
. Gold
. Green
. Red
. Yellow
Press F5 to run the project. Click the arrow at the right side of the combo box, and a
drop-down list appears, as shown in Figure 7.16.
Try typing in the text Magenta. Visual Basic lets you do this. Indeed, you can type
any text that you want. This may be the behavior you want, but more often you’ll
want to restrict a user to entering only values that appear in the list. To do this, you
change the DropDownStyle property of the combo box. Close the form to stop the
running project, and change the DropDownStyle property of the combo box to
DropDownList. Press F5 to run the project again, and try to type text into the combo
box. You can’t. The combo box doesn’t allow any text entry, so the user is limited to
selecting items from the list. As a matter of fact, clicking in the “text box” portion of
the combo box opens the list the same as though you clicked the drop-down arrow.
Stop the running project, and change the DropDownStyle back to DropDown. Next,
change the AutoCompleteSource property to ListItems and the AutoCompleteMode
property to Suggest. Run the project again, and type B in the combo box. The
FIGURE 7.16
Combo boxes
conserve space.
170 HOUR 7: Working with Traditional Controls
combo box opens and suggests items starting with B. Try changing
AutoCompleteMode to Append, and run the project again. This time, it fills the combo
box with the closest match as you type! This is a very handy interface to give users.
As you can see, the combo box and list box offer similar functionality; in fact, the
coding of their lists is identical. Each one of these controls serves a slightly different
purpose, however. Which one is better? That depends entirely on the situation. As
you use professional applications, pay attention to their interfaces; you’ll start to get
a feel for which control is appropriate in a given situation.
Summary
In this hour, you learned how to present text to a user. You learned that the Label
control is perfect for displaying static text (text the user can’t enter) and that the text
box is the control to use for displaying edited text. You can now create text boxes
that contain many lines of text, and you know how to add scrollbars when the text is
greater than what can be displayed in the control.
I don’t think I’ve ever seen a form without at least one button. You’ve learned how to
add buttons to your forms and how to do some interesting things such as add a picture
to a button. For the most part, working with buttons is a simple matter of
adding one to a form, setting its Name and Text properties, and adding some code to
its Click event—all of which you now know how to do.
Check boxes and option buttons are used to present true/false and mutually exclusive
options, respectively. In this hour, you learned how to use each of these controls
and how to use group boxes to logically group sets of related controls.
Finally, you learned how to use list boxes and combo boxes to present lists of items to
a user. You now know how to add items to a list at design time as well as runtime,
and you know how to sort items. The List Box and Combo Box are powerful controls,
and I encourage you to dig deeper into the functionality they possess.
Without controls, users would have nothing to interact with on your forms. In this
hour, you learned how to use the standard controls to begin building functional interfaces.
The controls discussed in this hour have been around since the early days of
Visual Basic. In fact, they still behave much as they did years ago. Keep in mind that I
only scratched the surface of each of these controls. Most do far more than I’ve hinted
at here. Mastering these controls will be easy, because you’ll be using them a lot. Also,
as you progress through this book, you will add code that saves the values the user
enters into these controls, and shows the values again when the form is displayed.
Workshop 171
Q&A
Q. Can I place radio buttons directly on a form?
A. Yes. The form is a container, so all radio buttons placed on a form are mutually
exclusive to one another. If you wanted to add a second set of mutually
exclusive buttons, they’d have to be placed on a container control. In general, I
think it’s best to place radio buttons in a group box rather than on a form. The
group box provides a border and a caption for the radio buttons. It’s also much
easier to move around the set of radio buttons when you’re designing the form.
(You simply move the group box.)
Q. I’ve seen what appear to be list boxes that have a check box next to each
item in the list. Is this possible?
A. Yes. In earlier versions of Visual Basic, this functionality was inherent in the
standard list box control. In Visual Basic 2010, this is accomplished using an
entirely different control: the checked list box.
Workshop
Quiz
1. Which control would you use to display text that the user can’t edit?
2. What common property is shared by the Label control and text box and
whose value determines what the user sees in the control?
3. What property must be set to True before you can adjust the height of a text
box control?
4. What is the default event of a Button control?
5. What do you call a button whose Click event is triggered when the user
presses Enter while another control has the focus?
6. Which control would you use to display a yes/no value to a user?
7. How would you create two distinct sets of mutually exclusive option buttons?
8. To manipulate items in a list, you use what collection?
9. What method adds an item to a list in a specific location?
172 HOUR 7: Working with Traditional Controls
Answers
1. The Label control
2. The Text property
3. The MultiLine property
4. The Click event
5. An Accept button
6. A check box
7. Place the radio buttons on two different container controls.
8. The Items collection
9. The Insert() method
Exercises
1. Use the skills you learned in the previous hours to set the tab order for your
Options form. Make the user name text box the first in the tab order. Be sure to
select an item before clicking your button!
2. Create a form with two list boxes. Add a number of items to one list box at
design time using the Properties window. Create a button that, when clicked,
removes the selected item in the first list and adds it to the second list.
173
HOUR 8
Using Advanced Controls
What You’ll Learn in This Hour:
. Creating timers
. Creating tabbed dialog boxes
. Storing pictures in an Image List control
. Building enhanced lists using the List View control
. Creating hierarchical lists using the Tree View control
The standard controls presented in Hour 7, “Working with Traditional Controls,”
enable you to build many types of functional forms. However, to create truly robust
and interactive applications, you must use the more advanced controls. As a Windows
user, you’ve encountered many of these controls, such as the Tab control, which
presents data on tabs, and the Tree View control, which displays hierarchical lists
such as the one in Explorer. In this hour, you’ll learn about these advanced controls
and how to use them to make professional interfaces like those you’re accustomed to
seeing in commercial products.
Many of the examples in this hour show you how to add items to collections at
design time. Keep in mind that everything you can do at design time you can also
accomplish using Visual Basic code.
By the
Way
174 HOUR 8: Using Advanced Controls
Creating Timers
All the controls you used in Hour 7 had in common the fact that the user can interact
with them. Not all controls have this capability—or restriction, depending on how
you look at it. Some controls are designed to be used only by the developer. One such
control is the Open File Dialog control you used in your Picture Viewer application
in Hour 1, “Jumping in with Both Feet: A Visual Basic 2010 Programming Tour.”
Another control that’s invisible at runtime is the Timer control. The Timer control’s
sole purpose is to trigger an event at a specified time interval.
Follow these steps to build a timer sample project:
1. Create a new Windows Application titled Timer Example.
2. Right-click Form1.vb in the Solution Explorer, choose Rename, and change the
name of the form to TimerExampleForm.vb.
3. Set the form’s Text property to Timer Example. (Remember to click the form
itself to view its properties.)
4. Add a new Timer control to your form by double-clicking the Timer item in the
toolbox (it’s located in the Components toolbox category).
The Timer control is invisible at runtime, so it’s added to the gray area at the bottom
of the screen rather than placed on the form, as shown in Figure 8.1.
Set the properties of the Timer control as follows:
Property Value
Name tmrClock
Enabled True
Interval 1000
You probably noticed that the Timer control has very few properties compared to the
other controls you’ve worked with; it doesn’t need many. The most important property
of the Timer control is the Interval property. It determines how often the Timer
control fires its Tick event (where you’ll place code to do something when the designated
time elapses). The Interval property is specified in milliseconds, so a setting of
1,000 is equal to 1 second, which is exactly what you set the Interval to for this
example. As with many controls, the best way to understand how the Timer control
works is to use it. Now you will create a simple clock using the Timer and a Label
control. The way the clock works is that the Timer control fires its Tick event once
Creating Timers 175
FIGURE 8.1
Invisible-atruntime
controls
are shown at the
bottom of the
designer, not on
a form.
Property Value
Name lblClock
AutoSize False
BorderStyle FixedSingle
Location 95, 120
Size 100, 23
Text Make blank (literally make this property empty)
TextAlign MiddleCenter
every second (because you’ve set the Interval property to 1,000 milliseconds).
Within the Tick event, you update the label’s Text property to the current system
time.
Add a new label to the form, and set its properties as follows:
The label’s AutoSize property determines whether the label automatically adjusts its
size when its Text property changes. Because we’re aligning the text to the middle of
the control, we don’t want it to autosize.
176 HOUR 8: Using Advanced Controls
Next, double-click the Timer control to access its Tick event. When a timer is first
enabled, it starts counting from 0 in milliseconds. When the number of milliseconds
specified in the Interval property passes, the Tick event fires, and the timer starts
counting from 0 once again. This cycle continues until and if the timer is disabled (its
Enabled property is set to False). Because you set the timer’s Enabled property to
True at design time, it starts counting as soon as the form on which it’s placed is
loaded. Enter the following statement in the Tick event:
lblClock.Text = TimeOfDay
TimeOfDay() is a handy function of Visual Basic that returns the current time of day
based on the system clock. So all this statement does is set the Text property of the
label to the current time of day. It’s important to remember that it does this once per
second. Press F5 to run the project. You see the Label control acting as a clock, updating
the time once every second, as shown in Figure 8.2.
Stop the running project, and save your work.
Timers are powerful, but you must take care not to overuse them. For a timer to work,
Windows must be aware of the timer and must constantly compare the current internal
clock to the timer’s interval. It does all this so that it can notify the timer at the
appropriate time to execute its Tick event. In other words, timers take system
resources. This isn’t a problem for an application that uses a few timers, but I wouldn’t
overload an application with a dozen timers unless I had no other choice (and
there’s almost always another choice).
FIGURE 8.2
Timers make it
easy to execute
code at specified
intervals.
Creating Tabbed Dialog Boxes 177
Creating Tabbed Dialog Boxes
Windows 95 was the first version of Windows to introduce a tabbed interface. Since
then, tabs have been widely adopted as a primary interface element. Tabs provide
two major benefits: a logical grouping of controls and a reduction of required screen
space. Although tabs might look complicated, they are actually easy to build and use.
You’ll add a set of tabs to your Options dialog box in your Picture Viewer program. In
this case, the tabs will be overkill, because you won’t have much on them, but the
point is to learn how they work, so follow these steps:
1. Start by opening the Picture Viewer project you completed in Hour 7.
2. Double-click OptionsForm.vb in the Solution Explorer to display it in the
designer.
3. Add a new Tab control to your form by double-clicking the TabControl item in
the toolbox (it’s located in the Containers toolbox category). The Tab control
defaults to having two tabs, which happens to be what you need for this example.
Set the Tab control’s properties as follows:
4. The tabs that appear on a Tab control are determined by the control’s TabPages
collection. Click the TabPages property of the Tab control in the Properties window,
and then click the small button that appears. Visual Basic shows the Tab-
Page Collection Editor. Your Tab control has two tabs by default, as shown in
Figure 8.3.
5. Each tab in the collection is called a page. Visual Basic names each new page
TabPageX, where X is a unique number. Although you technically don’t have to
change the name of a page, it’s easier to work with a Tab control if you give
each tab a meaningful name, such as pgeGeneralPage, pgePreferencesPage,
and so forth. The page TabPage1 is selected for you by default, and its properties
appear to the right. Change the tab’s name to pgeGeneral and set its Text
property (which is what actually appears on the tab) to General (you might
want to view the properties alphabetically to make this easier).
6. Click TabPage2 in the list on the left to select it. Change its Name property to
pgeAppearance and set its Text property to Appearance.
Property Value
Name tabOptions
Location 2, 2
Size 202, 94
178 HOUR 8: Using Advanced Controls
FIGURE 8.3
Use the TabPage
Collection Editor
to define tabs.
7. Click OK to save your changes.
Your Tab control now has two properly defined tabs (pages), as shown in Figure 8.4.
A quick way to add or remove a tab is to use the shortcuts provided in the
description pane at the bottom of the Properties window.
Did you
Know?
Each page on a Tab control acts as a container, much like a Panel or Group Box control.
This is why you can’t drag the Tab control by clicking in the middle of it. To drag
a container control, you have to click and drag the small image with the four arrows
FIGURE 8.4
Each tab should
have meaningful
text.
Creating Tabbed Dialog Boxes 179
that appears over the General tab (refer to Figure 8.4). Follow these steps to move the
options controls you created in Hour 7 to your new tabs:
1. Click the group box to select it (be sure not to click one of the radio buttons);
then right-click it and choose Cut.
2. Click the Tab control to select it.
3. Now that the Tab control is selected, click the Appearance page to switch to the
second page of the Tab control. Then click the center of the Appearance page.
4. Right-click in the center of the Appearance page and choose Paste.
5. Click the General tab to return to the first page of the Tab control.
6. Get the Tab control out of the way by dragging the Move image (the little
square with the directional arrows). Drag the tabs to the bottom of the form.
7. Click the User Name Label control to select it. Hold down the Shift key and
click the User Name text box, and then click the check box.
8. Press Ctrl+X to cut the selected controls from the form.
9. Click the Tab control to select it.
10. Right-click in the center of the General tab and choose Paste.
11. Set the Tab control’s Location property to 12, 12 and its Size property to
287, 145.
12. Click and drag the controls on the General tab so that they appear roughly centered
on the tab, as shown in Figure 8.5.
To wrap up the Tab control, click the Appearance tab to switch to the Appearance
page, and then move the group box to the middle of the page (by dragging and drop-
FIGURE 8.5
Tabs make it
easy to group
related controls.
180 HOUR 8: Using Advanced Controls
ping it). When you’re satisfied with its location, click the General tab again to switch
to the first page.
By understanding two simple programming elements, you’ll be able to do 99% of
what you need to with the Tab control. The first element is that you’ll need to know
which tab is selected at runtime. The control’s SelectedIndex property (not the
TabIndex property) sets and returns the index of the currently selected tab: 0 for the
first tab, 1 for the second, and so forth. The second thing to know is how to tell when
the user switches tabs. The Tab control has a SelectedIndexChanged event, which
fires whenever the selected tab is changed. In this event, you can check the value of
SelectedIndex to determine which tab the user selected.
Perhaps the trickiest issue with the Tab control is that each tab page has its own set
of events. If you double-click the tabs themselves, you get a set of global events for
the Tab control (this is where you’ll find the SelectedIndexChanged event). If you
double-click a page on the tabs, you get a unique set of events for that page; each
page has its own set of events.
Feel free to run your project now and check out how your tabs work. When you’re finished,
be sure to save your project.
Storing Pictures in an Image List
Control
Many of the controls I discuss in this hour can attach pictures to different types of
items. The Tree View control, which is used in Explorer to navigate folders, for example,
displays images next to each folder node. Not all these pictures are the same; the
control uses specific pictures to denote information about each node. It would have
been possible for Microsoft to make each control store its images internally, but that
would be highly inefficient because it wouldn’t allow controls to share the same pictures.
This would also cause a maintenance headache. For example, say that you
have 10 Tree View controls, and each displays a folder image for folder nodes. Now
it’s time to update your application, and you want to update the folder image to
something a bit nicer. If the image were stored in each Tree View control, you’d have
to update all 10 of them (and risk missing one). Instead, Microsoft created a control
dedicated to storing pictures and serving them to other controls: the Image List.
When you put images in an Image List control, it’s easy to share them among other
types of controls.
You won’t use the Picture Viewer for this section, so follow these steps to create a new
project:
1. Create a new Windows Application named Lists and Trees.
Storing Pictures in an Image List Control 181
2. Right-click Form1.vb in the Solution Explorer and rename it
ListsAndTreesForm.vb. Also, set its Text property to Lists and Trees.
3. Add a new Image List control by double-clicking the ImageList item in the
toolbox (it’s located in the Components toolbox category). As with the Timer
control, the Image List is an invisible-at-runtime control, so it appears below
the form, not on it. Change the name of the Image List to imgMyImages.
4. The sole purpose of an Image List control is to store pictures and make them
available to other controls. The pictures are stored in the control’s Images collection.
Click the Images property of the Image List control in the Properties
window, and then click the small button that appears. Visual Basic displays the
Image Collection Editor. Notice that this editor is similar to other editors you’ve
used in this hour.
5. Click Add to display the Open dialog box, and use this dialog box to locate and
select a 16×16 pixel icon. If you don’t have a 16×16 pixel icon, you can create a
BMP using Microsoft Paint, or download samples I’ve provided at http://www.
samspublishing.com/ and http://www.jamesfoxall.com/books.aspx. After
you’ve added an image, click OK to close the Image Collection Editor.
Take a look at the ImageSize property of the Image control. It should be 16, 16. If it
isn’t, the bitmap you selected might not be 16×16 pixels. This property should be set
to the dimensions of the first picture added to the Image List, but I’ve seen it not be
set automatically. If you’re using images of a different size, you might have to manually
change the ImageSize property to the correct dimensions.
You can’t always rely on the background where a picture will be displayed to be
white—or any other color, for that matter. The Image List control therefore has a
TransparentColor property. By default, the TransparentColor property is set to
Transparent. Because you used an icon file here, and icon files maintain their own
transparency information, you’ll leave this property alone. If you were using a BMP
file, or some other format that doesn’t retain transparency information, you would
want to use this property to designate a color in the bitmap that would appear transparent
when used with another control.
That’s all there is to adding images to an Image List control. The power of the Image
List lies not in properties or methods of the control itself, but in its ability to be
linked to other controls so that they can access the pictures the Image List stores.
You’ll do this in the next section.
182 HOUR 8: Using Advanced Controls
Building Enhanced Lists Using the List
View Control
The List View control is a lot like a list box on steroids—and then some. The List
View can be used to create simple lists, multicolumn grids, and icon trays. The right
pane in Windows Explorer is a List View. The primary display options available for
Explorer’s List View are Icons, List, Details, and Tiles. These correspond exactly to
the display options available for a List View by way of its View property. (You might
not know it, but you can change the appearance of the List View in Explorer by
right-clicking it and using the View submenu of the shortcut menu that appears.)
Now you’ll create a List View with a few items on it and experiment with the different
views—including showing a picture for the items, using the Image List from the
preceding section.
I can only scratch the surface of this great control here. After you’ve learned the
basics in this hour, I highly recommend that you spend some time with the List
View control, the help text, and whatever additional material you can find. I use
the List View all the time. It’s a powerful tool to have in your arsenal, because
displaying lists is a very common task.
Did you
Know?
Add a List View control to your form now by double-clicking the ListView item in
the toolbox. Set the properties of the List View as follows:
Property Value
Name lstMyListView
Location 8, 8
Size 266, 97
SmallImageList imgMyImages
View Details
As you can see, you can attach an Image List to a control via the Properties window
(and by using code as well, of course). Not all controls support the Image List,
but those that do make it as simple as setting a property to link to an Image List
control. The List View actually allows linking to two Image Lists: one for large
icons (32×32 pixels) and one for small images. In this example, you’ll use only small
pictures. If you wanted to use the large format, you could hook up a second Image
List containing larger images to the List View control’s LargeImageList property.
Building Enhanced Lists Using the List View Control 183
Creating Columns
When you changed the View property to Details, the control wanted to display a
header for the columns in the list. But because you haven’t yet defined columns, the
header doesn’t appear. The contents of this header are determined by the columns
defined in the Columns collection.
Follow these steps to create columns in your List View:
1. Select the Columns property in the Properties window and click the small button
that appears. Visual Basic displays the ColumnHeader Collection Editor window.
2. Click Add to create a new header, and change its Text property to Name and its
Width property to 120.
3. Click Add once more to create a second column, and change its Text property
to State. I haven’t had you change the names of the columns in this example
because you won’t refer to them by name.
4. Click OK to save your column settings, and close the window.
Your List View should now have two named columns, as shown in Figure 8.6.
Adding List Items
Follow these steps to add two items to the List View:
1. Click the Items property in the Properties window, and then click the small button
that appears to display the ListViewItem Collection Editor dialog box.
2. Click Add to create a new item, and change the item’s Text property to James
Foxall.
FIGURE 8.6
Use List
Views to present
multicolumn
lists.
184 HOUR 8: Using Advanced Controls
3. Open the drop-down list for the ImageIndex property. Notice how the list contains
the picture in the linked Image List control, as shown in Figure 8.7.
Select the image.
An item’s Text property determines the text displayed for the item in the List
View. If the View property is set to Details and multiple columns have been
defined, the value of the Text property appears in the first column. Subsequent
column values are determined by the SubItems collection.
4. Click the SubItems property (located in the Data category of the ListViewItem’s
properties). Then click the small button that appears, which displays the
ListViewSubItem Collection Editor.
5. Click Add to create a new subitem, and change its text to Nebraska.
6. Click OK to return to the ListViewItem Collection Editor.
7. Click the Add button to create another item. This time, change the Text property
to your name, and use the techniques you just learned to add a subitem.
For the Text property of the subitem, enter your state of residence. Go ahead
and give it an image, just as you did for my name.
8. When you’re finished, click OK to close the ListViewItem Collection Editor. Your
List View should now contain two list items, as shown in Figure 8.8.
FIGURE 8.7
Pictures from a
linked Image
List are readily
available to the
control.
Building Enhanced Lists Using the List View Control 185
FIGURE 8.8
List Views
offer much more
functionality than
a standard list
box.
9. Experiment with the View property of the List View control to see how the various
settings affect the control’s appearance. The Large Icons setting doesn’t display
an icon because you didn’t link an Image List control to the
LargeImageList property of the List View. Be sure to set the View property
back to Details before continuing.
10. Press F5 to run the project, and try selecting your name by clicking your state.
You can’t. The default behavior of the List View is to consider only the clicking
of the first column as selecting an item.
11. Stop the project, and change the FullRowSelect property of the List View to
True. Then run the project once more.
12. Click your state again. This time, your name becomes selected (actually, the
entire row becomes selected). I prefer to set up all my List Views with
FullRowSelect set to True, but this is just a personal preference. Stop the project
now, and save your work.
Manipulating a List View Using Code
You’ve just learned the basics of working with a List View control. Even though you
performed all the steps in Design view for this example, you’ll probably use code to
manipulate your list items because you won’t necessarily know ahead of time what to
display in the list. Next, I’ll show you how to work with the List View in code.
Adding List Items Using Code
Using Visual Basic code to add an item is simple—that is, if the item you’re adding is
simple. To add an item to your List View, you use the Add() method of the Items
collection, like this:
lstMyListView.Items.Add(“Mike Saklar”)
186 HOUR 8: Using Advanced Controls
If the item is to have a picture, you can specify the index of the picture as a second
parameter, like this:
lstMyListView.Items.Add(“Monte Sothmann”,0)
If the item has subitems, things get more complicated. The Add() method enables
you to specify only the text and image index. To access the additional properties of a
list item, you need to get a reference to the item in code. Remember that new items
have only one subitem by default; you have to create additional items. The Add()
method of the Items collection returns a reference to the newly added item. Knowing
this, you can create a new variable to hold a reference to the item, create the item,
and then use the variable to manipulate anything you choose to about the item. (See
Hour 11, “Using Constants, Data Types, Variables, and Arrays,” for information
about using variables.) The following code creates a new item and appends a subitem
to its SubItems collection:
Dim objListItem As ListViewItem
objListItem = lstMyListView.Items.Add(“Mike Hartman”, 0)
objListItem.SubItems.Add(“Nebraska”)
Determining the Selected Item in Code
The List View control has a collection that contains a reference to each selected item
in the control: the SelectedItems collection. If the MultiSelect property of the List
View is set to True (as it is by default), the user can select multiple items by holding down
the Ctrl or Shift key when clicking items. This is why the List View supports a
SelectedItems collection rather than a SelectedItem property. To gather information
about a selected item, you refer to it by its index. For example, to display the text of the first
selected item (or the only selected item if just one is selected), you could use code like this:
If lstMyListView.SelectedItems.Count > 0 Then
MessageBox.Show(lstMyListView.SelectedItems(0).Text)
End If
The reason you check the Count property of the SelectedItems collection is that if
no items are selected, a runtime error would occur if you attempted to reference element
0 in the SelectedItems collection.
Removing List Items Using Code
To remove a list item, use the Remove() method of the Items collection. The
Remove() method accepts and expects a reference to a list item. To remove the currently
selected item, for example, you could use a statement such as
lstMyListView.Items.Remove(lstMyListView.SelectedItems(0))
Creating Hierarchical Lists Using the Tree View Control 187
Again, you’d want to make sure that an item is actually selected before using this
statement.
Removing All List Items
If you’re filling a List View using code, you’ll probably want to clear the contents of
the List View first. That way, if the code to fill the List View is called a second time,
you won’t end up with duplicate entries. To clear the contents of a List View, use the
Clear() method of the Items collection, like this:
lstMyListView.Items.Clear()
The List View control is an amazingly versatile tool. As a matter of fact, I rarely use
the standard List Box control; I prefer to use the List View because of its added
functionality (such as displaying an image for an item). I’ve just scratched the surface
here, but you now know enough to begin using this powerful tool in your own
development.
Creating Hierarchical Lists Using the
Tree View Control
The Tree View control is used to present hierarchical data. Perhaps the most commonly
used Tree View control is found in Windows Explorer, where you can use the
Tree View to navigate the folders and drives on your computer. The Tree View is
perfect for displaying hierarchical data, such as an organizational chart of employees.
In this section, I’ll teach you the basics of the Tree View control so that you can
use this powerful interface element in your applications.
The Tree View’s items are contained in a Nodes collection, much like items in a List
View are stored in an Items collection. To add items to the tree, you append them to
the Nodes collection. As you can probably see by now, after you understand the basics
of objects and collections, you can apply that knowledge to almost everything in
Visual Basic. For instance, the skills you learned in working with the Items collection
of the List View control are similar to the skills needed for working with the Nodes
collection of the Tree View control. In fact, these concepts are similar to working
with list boxes and combo boxes.
Add a Tree View control to your form now by double-clicking the TreeView item in
the toolbox. Set the Tree View control’s properties as follows:
188 HOUR 8: Using Advanced Controls
Adding Nodes to a Tree View
Working with nodes at design time is similar to working with a List View’s Items
collection. So, I’ll show you how to work with nodes in code. To add a node you call
the Add() method of the Nodes collection (which you’ll do in this example). Add a
new button to your form, and set its properties as follows:
Double-click the button to access its Click event, and enter the following code:
tvwLanguages.Nodes.Add(“James”)
tvwLanguages.Nodes.Add(“Visual Basic”)
Press F5 to run the project, and then click the button. Two nodes appear in the tree,
one for each Add method call, as shown in Figure 8.9.
Notice how both nodes appear at the same level in the hierarchy; neither node is a
parent or child of the other. If all your nodes will be at the same level in the hierar-
Property Value
Name tvwLanguages
ImageList imgMyImages
Location 8, 128
Size 266, 97
Property Value
Name btnAddNode
Location 8, 231
Size 75, 23
Text Add Node
FIGURE 8.9
Nodes are the
items that
appear in a tree.
Creating Hierarchical Lists Using the Tree View Control 189
chy, consider using a List View control instead, because what you’re creating is simply
a list.
Stop the project, and return to the button’s Click event. Any given node can be both
a parent to other nodes and a child of a single node. (The parent node of any given
node can be referenced via the Parent property of a node.) For this to work, each
node has its own Nodes collection. This can be confusing, but if you keep in mind
that child nodes belong to the parent node, it starts to make sense.
Now you’ll create a new button that adds the same two nodes as before but makes
the second node a child of the first. Return to the Design view of the form, and then
create a new button and set its properties as shown:
Property Value
Name btnCreateChild
Location 89, 231
Size 80, 23
Text Create Child
Double-click the new button to access its Click event, and add the following code:
Dim objNode As TreeNode
objNode = tvwLanguages.Nodes.Add(“James”)
objNode.Nodes.Add(“Visual Basic”)
This code is similar to what you created in the List View example. The Add()
method of the Nodes collection returns a reference to the newly created node. Thus,
this code creates a variable of type TreeNode, creates a new node whose reference is
placed in the variable, and then adds a new node to the Nodes collection of the first
node. To see the effect this has, press F5 to run the project and click the new button.
You’ll see a single item in the list, with a plus sign to the left of it. This plus sign indicates
that child nodes exist. Click the plus sign, and the node is expanded to show its
children, as shown in Figure 8.10.
This example is a simple one—a single parent node having a single child node. However,
the principles used here are the same as those used to build complex trees with
dozens or hundreds of nodes.
190 HOUR 8: Using Advanced Controls
FIGURE 8.10
You can create
as deep a hierarchy
as you need
using the Tree
View control.
Removing Nodes
To remove a node, you call the Remove() method of the Nodes collection. The
Remove() method accepts and expects a valid node, so you must know which node to
remove. Again, the Nodes collection works much like the Items collection in the List
View control, so the same ideas apply. For example, the currently selected node is
returned in the SelectedNode property of the Tree View control. So, to remove the
currently selected node, you could use this statement:
tvwLanguages.Nodes.Remove(tvwLanguages.SelectedNode)
If this statement is called when no node is selected, an error occurs. In Hour 11, you’ll
learn all about data types and equalities, but here’s a preview: If an object variable
doesn’t reference an object, it’s equivalent to the Visual Basic keyword Nothing.
Knowing this, you could validate whether an item is selected with a bit of logic, using
code like the following. (Note that unlike with the List View control, only one node
can be selected at a time in a Tree View control)
If Not (tvwLanguages.SelectedNode Is Nothing) Then
tvwLanguages.Nodes.Remove(tvwLanguages.SelectedNode)
End If
By the Removing a parent node causes all its children to be removed as well.
Way
Clearing All Nodes
To clear all nodes in a Tree View, invoke the Clear() method of the Nodes collection:
tvwLanguages.Nodes.Clear()
As with the List View, I’ve only scratched the surface of the Tree View. Spend some
time becoming familiar with the basics of the Tree View, as I’ve shown here, and then
dig a bit deeper to discover the not-so-obvious power and flexibility of this control.
Workshop 191
Summary
Visual Basic includes a number of controls that go beyond the standard functionality
of the traditional controls discussed in Hour 7. In this hour, I discussed the most commonly
used advanced controls. You learned how to use the Timer control to trigger
events at predetermined intervals. You also learned how to use the Tab control to create
the tabbed dialog boxes with which you’re so familiar.
Also in this hour, you learned how to add pictures to an Image List control so that
other controls can use them. The Image List makes it easy to share pictures among
many controls, making it a useful tool. Finally, I taught you the basics of the List
View and Tree View controls—two controls you can use to build high-end interfaces
that present structured data. The more time you spend with all these controls, the
better you’ll become at creating great interfaces.
Q&A
Q. What if I need a lot of timers, but I’m concerned about system resources?
A. When possible, use a single timer for multiple duties. This is easy when two
events occur at the same interval—why bother creating a second timer? When
two events occur at different intervals, you can use some decision skills along
with static variables (discussed in Hour 11) to share Timer events.
Q. What else can I do with an Image List control?
A. You can assign a unique picture to a node in a Tree View control when the
node is selected. You can also display an image in the tab of a tab page in a Tab
control. Image List has many uses. As you learn more about advanced controls,
you’ll see additional opportunities for using images from an Image List.
Workshop
Quiz
1. What unit of time is applied to the Interval property of the Timer control?
2. What collection is used to add new tabs to a Tab control?
3. What property returns the index of the currently selected tab?
192 HOUR 8: Using Advanced Controls
4. True or false: You should use different Image List controls to store images of
different sizes.
5. For you to see columns in a List View control, the View property must be set
to what?
6. The additional columns of data that can be attached to an item in a List
View are stored in what collection?
7. What property of what object would you use to determine how many items are
in a List View?
8. What is each item in a Tree View control called?
9. How do you make a node the child of another node?
Answers
1. Milliseconds
2. The TabPages collection
3. The SelectedIndex property
4. True
5. Details
6. The SubItems collection
7. You check the Count property of the SelectedItems collection.
8. A node
9. You add it to the Nodes collection of the parent node.
Workshop 193
Exercises
1. Add a second Image List control to your project with the List View. Place an
icon (32×32 pixels) in this Image List, and set its ImageSize property to 32,
32. Next, link the Image List to the LargeImageList property of the List
View control. Change the View property to Large Icons or Tile, and see how the
large icons are used for these two views.
2. Create a new project, and add a List View, a button, and a text box to the
default form. Create a new item in the List View, using the text entered into
the text box when the button is clicked.
This page intentionally left blank
195
HOUR 9
Adding Menus and Toolbars
to Forms
What You’ll Learn in This Hour:
. Adding, moving, and deleting menu items
. Creating checked menu items
. Programming menus
. Implementing context menus
. Assigning shortcut keys
. Creating toolbar items
. Defining toggle buttons and separators
. Creating a status bar
The graphical user interface (GUI) you can use to interact with and navigate programs
is one of the greatest features of Windows. Despite this, a number of Windows
users still rely primarily on the keyboard, preferring to use the mouse only when
absolutely necessary. Data-entry people in particular never take their hands off the
keyboard. Many software companies receive support calls from angry customers
because a commonly used function is accessible only by using the mouse. Menus are
the easiest way to navigate your program for a user who relies on the keyboard, and
Visual Basic makes it easy than ever to create menus for your applications. In this
hour, you’ll learn how to build, manipulate, and program menus on a form. In addition,
I’ll teach you how to use the Toolbar control to create attractive and functional
toolbars. Finally, you’ll learn how to finish a form with a status bar.
196 HOUR 9: Adding Menus and Toolbars to Forms
Did you
Know?
Building Menus
When I said that Visual Basic makes building menus easier than ever, I wasn’t kidding;
building menus is an immediately gratifying process. I can’t stress enough how
important it is to have good menus, and because it’s so easy to do, there’s no excuse
for not putting menus in an application.
When running an application for the first time, users often scan the menus before
opening the manual. (Actually, most users never open the manual!) When you provide
comprehensive menus, you make your program easier to learn and use.
Creating Top-Level Menus
You add menus to a form by way of a control: the Menu Strip control. The Menu
Strip control is a bit odd. It’s the only control I know of (besides the Context Menu
Strip control, discussed later in this hour) that sits at the bottom of the form in the
space reserved for controls without an interface (like a Timer control) even though it
has a visible interface on the form.
Follow these steps to get started:
1. You’ll use the Picture Viewer project that you worked on in Hour 8, “Using
Advanced Controls,” so open that project now.
2. Double-click ViewerForm.vb in the Solution Explorer to display the main picture
viewer form in design view.
3. You’ll need room at the top of the form, so change the form’s Size.Height
property to 375.
4. Change the PictureBox’s Location to 8, 52 and its Size to 282, 279.
5. Select all the controls on the form except the picture box by Shift-clicking them
or lassoing them. Be sure to get the X and Y labels as well! After they’re all
selected, click and drag the Select Picture button until its top aligns with the
picture box (when you drag, all controls should move with the Select Picture
button). Your form should now look like Figure 9.1. Note that once you select
controls on a form, you can use the arrow keys to move them around, but the
snap lines won’t appear when you do so.
6. Add a new Menu Strip control to your form by double-clicking the MenuStrip
item in the toolbox (located in the Menus & Toolbars category), and change its
name to mnuMainMenu. As shown in Figure 9.2, the control is added to the pane
at the bottom of the Form Designer. Take a look at the top of the form—you see
the text Type Here.
Building Menus 197
FIGURE 9.1
You’ll need
space for menus
and toolbars at
the top of your
form.
7. Click the text Type Here, type &File, and press Enter. As you begin typing,
Visual Basic displays two new boxes that say Type Here, as shown in Figure 9.3.
FIGURE 9.2
A menu has no
items when first
added to a
form.
198 HOUR 9: Adding Menus and Toolbars to Forms
Notice the Properties window (if it’s not visible, press F4 to show it). The text you
just entered creates a new menu item. Each menu item is an object, and therefore,
the item has properties. By default, Visual Basic names the menu FileTool-
StripMenuItem. (You may need to click the new File menu item you created to
see its properties.) It’s a long name, but it gets the job done for now.
You might be wondering why I had you enter an ampersand (&) in front of the
word File. Take a look at your menu now, and you’ll see that Visual Basic doesn’t
display the ampersand; instead, it displays the text with the F underlined.
The ampersand, when used in the Text property of a menu item, tells Visual
Basic to underline the character immediately following it. For top-level menu
items, such as the File item you just created, this underlined character is called
an accelerator key. Pressing Alt plus an accelerator key opens the menu as if the
user had clicked it. You should avoid assigning the same accelerator key to
more than one top-level menu item on a form. To avoid conflicts, you can make
any character the accelerator character, not just the first character (for example,
typing F&ile would underline the i in File). When the menu item appears
on a drop-down menu (as opposed to being a top-level item), the underlined
character is called a hotkey. When a menu is visible (open), the user can press a
hotkey to trigger the corresponding menu item just as if it were clicked. Again,
don’t use the same hotkey for more than one item on the same menu.
You can use the ampersand in the Text property of button controls and some other
controls as well to create accelerator keys. For example, using “C&lick Me” for the
Text property of a button would allow the user to “click” the button by pressing Alt+L.
FIGURE 9.3
Creating a menu
item automatically
prepares
the control for
more items.
By the
Way
Building Menus 199
8. Click the Type Here text that appears to the immediate right of the File item,
enter &Tools, and press Enter. Visual Basic gives you two more Type Here
items—the same as when you entered the File item. Adding new menu items is
just a matter of clicking a Type Here box and entering the text for an item.
If you click a Type Here box below an existing menu item, you add a new item to
the same menu as the item above the box. If you click the Type Here box to the
right of a menu item, you create a submenu that uses the menu to the left of the
box as the entry point for the submenu. As you’ve seen, clicking the Type Here
box along the top of the menu bar creates a top-level menu.
By the
Way
Creating Menu Items for a Top-Level Menu
You can create as many top-level menus as you have room for on a form. For the Picture
Viewer, the File and Tools menus are adequate. Now you need to create the menu
items that a user can select for these top-level menus. Follow these steps to create the
menu items:
1. Click the File item to display a Type Here box below it. Click this Type Here box,
enter &Open Picture..., and press Enter.
2. Click the item you just created to give it the focus, and change the name of the
new item to mnuOpenPicture.
3. Click the Type Here box below the Open Picture item you just created, type
&Quit, and then press Enter. Change the name of the new item to mnuQuit.
Now is a good time to save your work, so click Save All on the toolbar.
4. Click the Tools menu to select it. This displays a Type Here box to the right of
and below the Tools item. Click the Type Here box below the Tools menu, type
&Draw Border, and press Enter. Change the name of the new item to
mnuDrawBorder.
5. This part can be tricky. Hover the pointer over the Type Here box below the
Draw Border item. A small drop-down arrow appears. Click this arrow and
select Separator, as shown in Figure 9.4. This drop-down is used to specify what
type of item you want on the menu. You can create a combo box or a text box
or, as in this case, a separator to isolate groups of unrelated menu items.
6. After you choose Separator, a line appears under Draw Border, and a new Type
Here box appears. Click this box to select it, enter the text &Options..., and
then press Enter to create the menu item. Change the name of this new item to
mnuOptions.
7. Click the picture box or some other control to stop editing the menu.
200 HOUR 9: Adding Menus and Toolbars to Forms
FIGURE 9.4
You can create
text boxes,
combo boxes,
and separators
in addition to
regular menu
items.
Moving and Deleting Menu Items
Deleting and moving menu items are even easier than adding new items. To delete a
menu item, right-click it and choose Delete from the context menu that appears. To
move an item, drag it from its current location and drop it in the location in which
you want it placed.
Creating Checked Menu Items
A menu item that isn’t used to open a submenu can display a check mark next to its
text. Check marks are used to create menu items that have state—the item is either
selected or it isn’t. Now you’ll create a checked menu item. Remember from Hour 7,
“Working with Traditional Controls,” the check box you created for the Options form?
It was used to specify whether the user should be prompted before the Picture Viewer
closes. Now you’ll create a menu item for this as well. Follow these steps:
1. Click the File menu to open it.
2. Click the Type Here box below the Quit menu item, enter Confirm on Exit, and
press Enter. Change the name of the new item to mnuConfirmOnExit.
3. Right-click Confirm on Exit, and choose Checked from the shortcut menu, as
shown in Figure 9.5. If your menu is different from the one shown in Figure 9.5,
click a different menu item, and then right-click the Confirm on Exit item. You
also could click the menu item and change its Checked property in the Properties
window.
4. Click and drag the Confirm on Exit item, and drop it on the Quit menu item.
This moves the item above the Quit item. Your menu now looks like Figure 9.6.
Building Menus 201
FIGURE 9.5
Menu items can
be used to indicate
state.
Press F5 to run the project. The menu appears on your form, just as you designed it
(see Figure 9.7). Click the File menu to open it, and then click Quit; nothing happens.
In fact, the checked state of your menu item doesn’t change even if you click that
item. In the next section, I’ll show you how to add code to menu items to make them
actually do something (including changing their checked state).
Stop the project now, and save your work.
FIGURE 9.6
Menus are created
in an interactive
fashion.
202 HOUR 9: Adding Menus and Toolbars to Forms
FIGURE 9.7
Menus appear at
runtime the
same as they do
at design time.
Programming Menus
Every menu item is a unique object. You could actually edit each item by clicking it to
select it and then changing the item’s properties in the Properties window. Although
individual menu items aren’t controls per se, adding code behind them is similar to
adding code behind a control. Now you’ll add code to menu items you created.
Follow these steps to create the code for the menus:
1. Click the File menu to open it.
2. Double-click the Open Picture menu item. Just as when you double-click a control,
Visual Basic displays the code editor with the default event for the menu
item you’ve clicked. For menu items, this is the Click event.
3. Enter the following code:
’ Show the open file dialog box.
If ofdSelectPicture.ShowDialog = DialogResult.OK Then
‘ Load the picture into the picture box.
picShowPicture.Image = Image.FromFile(ofdSelectPicture.FileName)
‘ Show the name of the file in the form’s caption.
Me.Text = “Picture Viewer (“ & ofdSelectPicture.FileName & “)”
End If
This is the exact code you entered for the Select Picture button you created in
Hour 1, “Jumping in with Both Feet: A Visual Basic 2010 Programming Tour,”
so I won’t discuss it here.
4. Double-click ViewerForm.vb in the Solution Explorer window to switch back to
the Form Designer for the Picture Viewer form.
Building Menus 203
5. Double-click the Confirm on Exit menu item to access its Click event. Enter the
following code statement:
mnuConfirmOnExit.Checked = Not(mnuConfirmOnExit.Checked)
When Confirm on Exit is clicked, this code sets the item’s checked state to the
opposite of the item’s current checked state. The function Not() is used to
negate a Boolean (true or false) value. Don’t worry; I discuss this in detail in
Hour 12, “Performing Arithmetic, String Manipulation, and Date/Time Adjustments.”
For now, realize that if the current value of the Checked property is
True, Not() returns False. If Checked currently is False, Not() returns True.
Therefore, the checked value toggles between True and False each time the
menu item is clicked.
6. Double-click ViewerForm.vb in the Solution Explorer window (or click the ViewerForm.
vb [Design] tab) to switch back to the Form Designer for the Picture
Viewer form again.
7. Double-click the Quit menu item to access its Click event, and enter the following
code:
Me.Close()
Again, recall from Hour 1 that this statement simply closes the form. This has
the effect of closing the application, because it’s the only form that’s loaded.
8. Return to the form viewer yet again, click Tools to display the Tools menu, and
then double-click the Draw Border menu item to access its Click event. Enter
the following code:
Dim objGraphics As Graphics
objGraphics = Me.CreateGraphics
objGraphics.Clear(System.Drawing.SystemColors.Control)
objGraphics.DrawRectangle(System.Drawing.Pens.Blue, _
picShowPicture.Left - 1, _
picShowPicture.Top - 1, _
picShowPicture.Width + 1, picShowPicture.Height + 1)
objGraphics.Dispose()
This code is also directly from Hour 1, so refer to that hour for the specifics on
how this code works.
204 HOUR 9: Adding Menus and Toolbars to Forms
9. Return to the Form Designer, double-click the Options menu item, and enter the
following code in its Click event:
OptionsForm.ShowDialog()
You have just added all the code necessary for your menu to function. Follow these
steps to test your work:
1. Press F5 to run the project. Open the File menu by pressing Alt+F (remember,
the F is the accelerator key).
2. Click the Confirm on Exit button. The menu closes, so click File again to open
it; notice that the item is no longer checked. Clicking it again would check it.
3. Click all the menu items except Quit to make sure that they work as expected.
When you’re finished, choose File, Quit to close the running project.
If you selected Confirm on Exit, you might have noticed that you weren’t asked
whether you really wanted to quit. That’s because the quit code hasn’t been written to
consider the checked state of the Ask Before Closing button. You’ll hook up this item,
as well as all the other options, in Hour 11, “Using Constants, Data Types, Variables,
and Arrays.”
When designing your menus, look at some of the many popular Windows applications
available and consider the similarities and differences between their menus
and yours. Although your application might be unique and therefore have different
menus from other applications, there are probably similarities as well (such as
Cut, Copy, Paste, Open, and so on). When possible, make menu items in your
application follow the same structure and design as similar items in the popular
programs. This will shorten the learning curve for your application, reduce user
frustration, and save you time.
Did you
Know?
Implementing Context Menus
Context menus (also called shortcut menus) are the pop-up menus that appear when
you right-click an object on a form. Context menus get their name from the fact that
they display context-sensitive choices—menu items that relate directly to the object
that’s right-clicked. Most Visual Basic controls have a default context menu (also
called a shortcut menu), but you can assign custom context menus if you want. Creating
context menus is much like creating regular menus. To create context menus,
however, you use a different control: the Context Menu Strip control.
Follow these steps to implement a custom context menu in your project:
1. Display the ViewerForm.vb form in the Form Designer.
Building Menus 205
2. Add a new context menu strip to the form by double-clicking the Context Menu
Strip item in the toolbox. Like the Main Menu control, the Context Menu Strip
control is placed in the pane below the Form Designer. Change its name to
mnuPictureContext.
3. When the Context Menu Strip control is selected, a context menu appears
toward the top for editing. Click the Type Here box, enter the text Draw Border
(see Figure 9.8), and press Enter to create the menu item. You’ve just created a
context menu with a single menu item.
4. Double-click the new menu item to access its Click event, and enter the following
code:
Dim objGraphics As Graphics
objGraphics = Me.CreateGraphics
objGraphics.Clear(System.Drawing.SystemColors.Control)
objGraphics.DrawRectangle(System.Drawing.Pens.Blue, _
picShowPicture.Left - 1, _
picShowPicture.Top - 1, _
picShowPicture.Width + 1, picShowPicture.Height + 1)
objGraphics.Dispose()
Yes, this is exactly the same code you entered for the Draw Border menu item
and the Draw Border button. It seems sort of redundant to enter the same code
in three places, doesn’t it? In Hour 10, “Creating and Calling Code Procedures,”
FIGURE 9.8
Context menus
are edited in
much the same
way as regular
menus.
206 HOUR 9: Adding Menus and Toolbars to Forms
I’ll show you how to share code so that you don’t have to enter it in multiple
places!
5. Double-click ViewerForm.vb in the Solution Explorer to return to the designer
for the Picture Viewer form.
6. You link a control to a context menu by setting a property. Click the picture box
on the form now to select it, and then change the ContextMenuStrip property
of the picture box to mnuPictureContext; the context menu is now linked to
the picture box.
7. Press F5 to run the project, and right-click the picture box. You see the context
menu shown in Figure 9.9. Go ahead and choose Draw Border, and the border
will be drawn.
8. Stop the project, and save your work.
Assigning Shortcut Keys to Menu Items
If you’ve spent any time learning a Microsoft application, you’ve most likely learned
some keyboard shortcuts. For example, pressing Ctrl+P in any application that prints
has the same effect as opening the File menu and choosing Print.
Add shortcuts to your menus now by following these steps:
1. Click the File menu at the top of the form to open it, and then click Open Picture.
2. In the Properties window, click the ShortcutKeys property, and then click the
down arrow that appears. This drop-down, shown in Figure 9.10, enables you
to define a shortcut key for the selected menu item.
FIGURE 9.9
Context menus
make handy
shortcuts.
Using the Toolbar Control 207
3. Check Ctrl and then select O (for Open) from the Key drop-down menu; then
click another property to close the drop-down.
4. Press F5 to run the project once more. Next, press Ctrl+O. The application
behaves as though you opened the File menu and clicked the Open Picture item.
Although it isn’t always possible, try to assign logical shortcut key combinations.
The meaning of F6 is hardly intuitive, for example. But, when assigning modifiers
such as Ctrl with another character, you have some flexibility. For instance, the key
combination of Ctrl+Q might be a more intuitive shortcut key for Quit than Ctrl+T.
Again, if the menu item is the same as or similar to a menu item in a commercial
application, use the same shortcut key as the commercial application does.
Did you
Know?
Stop the running project, and save your work before continuing.
Using the Toolbar Control
Generally, when a program has a menu (as most programs should), it should also
have a toolbar. Using a toolbar (called a toolstrip in Visual Basic for some reason) is
one of the easiest ways for a user to access program functions. Unlike menu items,
toolbar items are always visible and therefore are immediately available. In addition,
toolbar items have ToolTips, which enable a user to discover a tool button’s purpose
simply by hovering the mouse pointer over the button.
FIGURE 9.10
Use the
ShortcutKeys
property of a
menu item to
assign a shortcut
key.
208 HOUR 9: Adding Menus and Toolbars to Forms
Toolbar items are really shortcuts for menu items; every item on a toolbar should
have a corresponding menu item. Remember, some users prefer to use the keyboard,
in which case they need to have keyboard access to functions via menus.
The actual items you place on a toolbar depend on the features the application supports.
However, the mechanics of creating toolbars and toolbar items are the same regardless
of the buttons you choose to use. You create toolbars by using the ToolStrip control.
Follow these steps to add a toolbar to the main form in your Picture Viewer project:
1. Display the ViewerForm.vb form in the Form Designer (if it’s not already displayed).
2. Add a new ToolStrip control to your form by double-clicking the ToolStrip
item in the toolbox. A new toolbar is added to the top of your form. Change the
name of the toolbar to tbrMainToolbar.
3. Notice that the toolbar appears above the menu. Anyone who has used a Windows
application knows that a toolbar belongs below the menu bar. Right-click
the toolbar and choose Bring To Front from its shortcut menu. That causes the
toolbar to move below the menu. Your form should now look like Figure 9.11.
Adding Toolbar Buttons Using the Buttons
Collection
Like many other controls you’ve already learned about, the ToolStrip control supports
a special collection: Items. The Items collection contains the buttons that appear
on the toolbar. Click the Items property in the Properties window, and then click the
small button that appears; the Items Collection Editor appears. The list of members
shows the toolbar itself, but no buttons, because new toolbars have no buttons.
FIGURE 9.11
New toolbars
have no
buttons.
Using the Toolbar Control 209
You’ll add three images to your toolbar: one for Open, one for Draw Border, and
one for Options. You can download these images from my website, http://www.
jamesfoxall.com/books.aspx.
By the
Way
Open the drop-down list in the upper-left corner, as shown in Figure 9.12. This list
contains the types of items that can be added to a toolbar.
For this example, you will create buttons and separators. Feel free to experiment with
the different item types in another project. Follow these steps:
1. Click Button in the drop-down list to create a new button. Set its properties as follows
(you might want to change the property display sort order to Alphabetical):
Property Value
Name tbbOpenPicture
Text Open Picture
ToolTipText Open Picture
FIGURE 9.12
Toolbars may
contain a number
of different
types of items.
2. Click the Image property for the button, and then click the Build button that
appears. Click Import, and then browse and select the Open image.
3. Click OK to save the image in the button.
7. Set the Image property of the Options button to a valid image file.
You’ve now created the buttons for your toolbar. There’s one last thing you should
do, however. Professional designers always separate related groups of tool buttons
using a separator. A separator is a vertical line that appears between two buttons. All
three of the buttons you’ve created are relatively unrelated, so now you’ll create separators
to isolate them from one another. Follow these steps:
1. Choose Separator from the drop-down list to create a separator. The separator
is added at the end of the row of buttons. Click and drag the separator and
drop it on the Draw Border button. This moves the separator so that it appears
in front of the Draw Border button.
2. Choose Separator from the drop-down again to create a new separator. Click
and drag this separator and drop it on the Options button. This moves the separator
between the Draw Border button and the Options button.
3. Click the form to deselect the toolbar control. Your screen should look like
Figure 9.13.
210 HOUR 9: Adding Menus and Toolbars to Forms
Property Value
Name tbbOptions
Text Options
ToolTipText Options
5. Set the Image property of the Draw Border button to a valid image file.
6. Open the drop-down once more and click Button to create a new button. Set its
properties as follows:
You can use the Items Collection Editor to add items to a toolbar, rather than
adding them dynamically as shown in this example.
By the
Way
4. Open the drop-down once more and click Button to create a new button. Set its
properties as follows:
Property Value
Name tbbDrawBorder
Text Draw Border
ToolTipText Draw Border
Using the Toolbar Control 211
FIGURE 9.13
Your toolbar is
now ready for
some code to
make it work.
Programming Toolbars
Programming toolbars is pretty much the same as programming menus. As you will
see, Microsoft has chosen to standardize things whenever possible. For example, in
early versions of .NET, you worked with a Toolbar control that had a Buttons collection.
In 2005, the Toolbar control was replaced with a Toolstrip control that has
an Items collection. The List View control has an Items collection, as does the
Tree View control. Seeing a pattern? After you learn how to work with the Items
collection of one control, it’s an easy transition to work with the Items collection of
other controls.
Follow these steps to make your toolbar functional:
1. Click the tbrMainToolbar control below the form to select it.
2. Double-click the Open button on the toolbar to access its Click event. Be sure
to click the button and not the toolbar. Double-clicking the toolbar accesses a
different event altogether. Enter the following code:
’ Show the open file dialog box.
If ofdSelectPicture.ShowDialog = DialogResult.OK Then
‘ Load the picture into the picture box.
picShowPicture.Image = Image.FromFile(ofdSelectPicture.FileName)
‘ Show the name of the file in the form’s caption.
Me.Text = “Picture Viewer(“ & ofdSelectPicture.FileName & “)”
End If
3. Click the ViewerForm.vb [Design] tab to return to Form Design view.
212 HOUR 9: Adding Menus and Toolbars to Forms
4. Double-click the Draw Border button, and add the following code to its
Click event:
Dim objGraphics As Graphics
objGraphics = Me.CreateGraphics
objGraphics.Clear(System.Drawing.SystemColors.Control)
objGraphics.DrawRectangle(System.Drawing.Pens.Blue, _
picShowPicture.Left - 1, _
picShowPicture.Top - 1, _
picShowPicture.Width + 1, picShowPicture.Height + 1)
objGraphics.Dispose()
5. Click the ViewerForm.vb [Design] tab to return to Form Design view.
6. Double-click the Options button, and add the following code to its Click event:
OptionsForm.ShowDialog()
Go ahead and save your work, and then press F5 to run the project. Clicking the toolbar
buttons should now perform the same actions as clicking the menu items. In
Hour 10, I’ll show you how the two controls can share code.
Creating Drop-Down Menus for Toolbar Buttons
Although you won’t use one in this project, be aware that you can create drop-down
menus on toolbars, as shown in Figure 9.14. Visual Basic 2010 uses these in a number
of places. To create a menu like this, rather than add a regular button to the toolbar,
you add a DropDownButton. Doing so creates a submenu just as it did when you
defined regular menus earlier in this hour.
FIGURE 9.14
You can create
drop-down
menus like
these.
Creating a Status Bar 213
Creating a Status Bar
The last control I’ll show you is the Status Bar control. The Status Bar isn’t nearly
as fancy, or even as useful, as other controls such as the ToolStrip or MenuStrip,
but it’s also not as difficult to work with, either. A status bar adds value to an application
in that it makes information available in a standard location, and users have
come to expect it. In its simplest form, a status bar displays a caption and sizing grip—
the dots to the right of the control that the user can drag to change the form’s size.
Add a new status bar to the form now by double-clicking the StatusStrip item in the
toolbox (located in the Menus & Toolbars category). You need to use the vertical
scrollbar to the right in the designer to scroll down and see the status bar at the bottom
of your form. Change the name of the StatusStrip to sbrMyStatusStrip.
Because of how you have anchored your other controls, the status strip overlays a
few controls at the bottom of the form. Fix this now by following these steps:
1. Click the PictureBox on the form, and change its Size property to 265, 256.
2. Change the Location.Y property of the Shrink and Enlarge buttons to 285.
Your form should now look like Figure 9.15.
FIGURE 9.15
Status bars
always appear at
the bottom of a
form.
Click the StatusStrip to select it, and take a look at its left edge. Does it look familiar?
It’s similar to the interface you have for adding menu items to MenuStrips and
buttons to ToolStrips. Click the drop-down arrow, and choose Status Label. A new status
label appears. Change its properties as follows:
214 HOUR 9: Adding Menus and Toolbars to Forms
Property Value
Name lblStatus
Text No image loaded
You probably noticed when you opened the drop-down to create the status label that
you can place items of other types on the status strip as well. For now, the label will do.
In Hour 10, you’ll write code to display the name of the opened picture in the label.
Press F5 to run the project. Move the mouse pointer over the small set of dots in the
status strip’s lower-right corner. The pointer changes to a sizing arrow. You can click
and drag to resize the form. However, the status strip isn’t smart enough to realize
when a form’s border can’t be resized (for example, when the form’s border style is
set to fixed or fixed tool window). You have to change the SizingGrip property of
the status strip to False to hide the grip.
Summary
Menus, toolbars, and status bars add tremendous value to an application by greatly
enhancing its usability. In this hour, you learned how to use the MenuStrip control
to build comprehensive menus for your applications. You learned how to add, move,
and delete menu items and how to define accelerator and shortcut keys to facilitate
better navigation via the keyboard. You also saw how toolbars provide shortcuts for
accessing common menu items. You learned how to use the ToolStrip control to create
functional toolbars, complete with bitmaps and logical groupings. Finally, you
discovered how to use a status strip to dress up the application. Implementing these
items is an important part of the interface design process for an application. You
now have the skills necessary to start putting them into your own programs.
Workshop 215
Q&A
Q. I have a number of forms with nearly identical menus. Do I really need to
take the time to create menus for all these forms?
A. Not as much as you might think. Create a MenuStrip control that has the
common items on it, and then copy and paste the control to other forms. You
can then build on this menu structure, saving yourself a lot of time. Be aware,
though, that when you copy and paste a control, the corresponding code does
not get copied.
Q. I’ve seen applications that allow the end user to customize the menus and
toolbars. Can I do that with the Visual Basic menus and toolbars?
A. No. To accomplish this behavior, you’ll have to purchase a third-party component—
or write a lot of code to make this happen. Personally, I think buying a
component that supports this functionality is a much better option.
Workshop
Quiz
1. True or false: You use the Context Menu Strip control to create form menu bars.
2. To create an accelerator, or hotkey, with what do you preface the character?
3. To place a check mark next to a menu item, you set what property of the item?
4. How do you add code to a menu item?
5. Toolbar items are part of what collection?
6. True or false: Every button on a toolbar has its own Click event.
7. What control displays information to the user at the bottom of a form?
216 HOUR 9: Adding Menus and Toolbars to Forms
Answers
1. False. You use the MenuStrip control.
2. An ampersand (&)
3. The Checked property
4. Double-click the menu item.
5. The Items collection
6. True
7. The StatusStrip control
Exercises
1. Create a new project, and build a ToolStrip that has a drop-down button.
2. Using the ToolStrip control, figure out how to display status text in place of a
button. (Hint: A special type of item in the Items collection does this.)
Creating Visual Basic Code Modules 217
HOUR 10
Creating and Calling Code
Procedures
What You’ll Learn in This Hour:
. Creating Visual Basic code modules
. Creating code procedures
. Calling procedures
. Passing parameters
. Exiting procedures
. Avoiding recursive procedures
You’ve now spent about nine hours building the basic skills necessary to navigate
Visual Basic and to create an application interface. Creating a good interface is
important, but it’s only one of many steps toward creating a Windows program. After
you’ve created the basic interface of an application, you need to enable the program
to do something. The program might perform an action all on its own, or it might
perform actions based on a user interacting with the GUI. Either way, you write
Visual Basic code to make your application perform tasks. In this hour, you’ll learn
how to create sets of code (called modules), how to create isolated code routines that
can be executed (called procedures), and how to invoke the procedures you create.
Creating Visual Basic Code Modules
A module is a place to store the code you write. Before you can begin writing Visual
Basic code, you must start with a module. You’ve already worked with one type of
module: a form module (refer to Hour 5, “Building Forms: The Basics,” for more information).
When you double-click an object on a form, you access events that reside in
the form module. In addition to form modules, you can create standard modules or
class modules.
218 HOUR 10: Creating and Calling Code Procedures
Class modules are used as templates for the instantiation of objects. I discuss
the specifics of creating such objects in Hour 16, “Designing Objects Using
Classes.” Most of the techniques discussed in this hour apply to class modules,
but I’ll focus this discussion on standard modules because they’re easier to use.
By the
Way
Although you could place all your program’s code in a single standard module or
even in a class module, it’s best to create different modules to group related sets of
code. In addition, if code is called from within only one form, it’s often best to place
that code in the form’s module. You’ll be placing code within a form module, as well
as within a new module that you’ll create in this hour.
The current development trend centers on object-oriented programming (OOP,
which revolves around class modules). I’ll give you a primer on OOP in Hour 16,
but it’s an advanced topic, so I don’t cover it in detail. I highly recommend that you
read a dedicated object-oriented programming book, such as Sams Teach Yourself
Object-Oriented Programming with Visual Basic .NET in 21 Days, Second Edition
(Sams Publishing, 2002), after you’re comfortable with the material in this book.
By the
Way
The primary general rule for using standard modules is that you should create modules
to group related sets of code. This isn’t to say that you should create dozens of
modules. Rather, group related functions into a reasonably sized set of modules. For
example, you might want to create one module that contains all your printing routines
and another that holds your data-access routines. In addition, I like to create a
general-purpose module in which to place all the various routines that don’t necessarily
fit in more specialized modules.
It’s often preferable to create classes and instantiate objects rather than use
standard modules, but no rules are set in stone. Some OOP purists suggest
(strongly) that you never use a standard module. Remember that a standard module
is simply a tool, and all tools have a purpose.
By the
Way
You’ll build on the Picture Viewer application from Hour 9, “Adding Menus and Toolbars
to Forms,” so open that now.
Next, create a new standard module by choosing Project, Add New Item. When the
Add New Item dialog box appears, scroll down and click Module (see Figure 10.1).
Note that this is the same dialog box used to add new forms. Change the name of the
module to DrawingModule.vb, and click Add to create the new module. Visual Basic
creates the new module and positions you in the code window, ready to enter code, as
shown in Figure 10.2.
Save your project now by clicking Save All on the toolbar.
Writing Code Procedures 219
FIGURE 10.1
All new project
items are added
from within this
dialog box.
FIGURE 10.2
Modules have no
graphical interface,
so you
always work with
them in the code
editor.
Writing Code Procedures
After you’ve created the module(s) in which to store your code, you can begin to write
Visual Basic code procedures. A procedure is a discrete set of code that can be called
from other code. Procedures are much like events, but rather than being executed by
a user interacting with a form or control, procedures are executed when called by a
code statement.
220 HOUR 10: Creating and Calling Code Procedures
Visual Basic has two types of procedures:
. Procedures that return a value (called functions)
. Procedures that do not return a value (called subroutines)
There are many reasons to create a procedure that returns a value. For example, a
function can return True or False, depending on whether it was successful in completing
its task. You could also write a procedure that accepts certain parameters
(data passed to the procedure, in contrast to data returned by the procedure) and
returns a value based on those parameters. For instance, you could write a procedure
that enables you to pass it a sentence, and in return it passes back the number of
spaces in the sentence. The possibilities are limited only by your imagination. Just
keep in mind that a procedure doesn’t have to return a value.
Declaring Procedures That Don’t Return Values
To create a procedure, whether it be a Sub (a procedure that doesn’t return a value) or
a Function (a procedure that returns a value), you first declare it within a module. In
your new module, type the following and press the Enter key:
Public Sub OpenPicture()
When you press Enter, Visual Basic automatically inserts a blank line and creates the
text End Sub, as shown in Figure 10.3. You’ve just created a new procedure.
FIGURE 10.3
The Public
Sub and End
Sub statements
create the basic
structure of a
Sub procedure.
Writing Code Procedures 221
The declaration of a procedure (the statement used to define a procedure) has a number
of parts. The first word, Public in this case, is a keyword (that is, a word with a
special meaning in Visual Basic). Public defines the scope of this procedure (scope is
discussed in detail in Hour 11, “Using Constants, Data Types, Variables, and Arrays”).
Public specifies that the procedure can be called from code contained in modules
other than the one containing the defined procedure. You can use the keyword
Private in place of Public to restrict access to the procedure to code in the module in
which the procedure resides. Because you’ll call this code from the Picture Viewer
form, you need to make the procedure Public.
The scope designator is optional. If it’s omitted, a Public procedure is created.
You should always explicitly designate the scope of your procedures.
By the
Way
The word Sub (short for subroutine) is another Visual Basic keyword. Sub is used to
declare a procedure that doesn’t return a value. Later in this hour, you’ll learn how to
create procedures that return values (called functions).
The third word, OpenPicture, is the actual name of the procedure. It can be just
about any string of text you want it to be. Note, however, that you can’t assign a
name that’s a keyword, nor can you use spaces within a name. In the example you’re
building, the procedure will perform the same function as the Open Picture menu
item and the Toolstrip button—hence the name. You should always give procedures
strong names that reflect their purpose. You can have two procedures with the same
name only if they have different scope (again, scope is discussed in Hour 11.
Some programmers prefer the readability of spaces in names, but in many
instances, such as when you’re naming procedures, spaces can’t be used. A common
technique is to use an underscore (_) in place of a space, such as in
Open_Picture, but I recommend that you just use mixed case (both uppercase
and lowercase letters), as you have in this example.
Did you
Know?
Immediately following the name of the procedure is a set of parentheses. The
OpenPicture() procedure doesn’t accept any parameters (data passed in), so the
parentheses are left empty. If you wanted calling code to pass data into this procedure,
you would do so within these parentheses. I’ll show you how to do that later in
this hour.
You have to supply parentheses, even when a procedure doesn’t accept any
parameters.
By the
Way
222 HOUR 10: Creating and Calling Code Procedures
Add the following code to your OpenPicture() procedure:
’ Show the open file dialog box.
If ViewerForm.ofdSelectPicture.ShowDialog = DialogResult.OK Then
‘ Load the picture into the picture box.
ViewerForm.picShowPicture.Image = _
Image.FromFile(ViewerForm.ofdSelectPicture.FileName)
‘ Show the name of the file in the statusbar.
ViewerForm.sbrMyStatusStrip.Items(0).Text = _
Viewerform.ofdSelectPicture.FileName
End If
Notice that this code is almost identical to the code you entered in the Open Picture
button, menu item, and Toolstrip button from previous hours. The difference is that,
because this module is separate from the form, you have to explicitly name the form
when referencing controls on the form or when getting or setting the form’s properties
(you can’t use Me). Also notice that you enter code to show the selected filename in
the status strip, as opposed to in the form’s caption.
You’ve already entered this code (or a variation of it) in three places. Earlier, I alluded
to the idea that this isn’t optimal and that we would address it. Whenever you find
yourself duplicating code, you should realize that the duplicated code should be
placed in a procedure. Then, rather than duplicating the code, you can just call the
procedure as needed. This approach has a number of advantages, including:
. Reduction of errors: Each time you enter code, you run the risk of doing something
wrong. By entering code only once, you reduce the likelihood of introducing
errors.
. Consistency and maintainability: When you duplicate code, you often forget
all the places where that code is used. You might fix a bug in one location but
not in another, or add a feature to one copy of the code but not another. By
using a single procedure, you have to worry about maintaining only one
instance of the code.
Now you’ll create a procedure to draw a border around the picture box. Position the
cursor after the words End Sub, press Enter, and type the following code where shown
in Figure 10.4:
Public Sub DrawBorder(ByRef objPicturebox As PictureBox)
Dim objGraphics As Graphics
objGraphics = objPicturebox.Parent.CreateGraphics
objGraphics.Clear(System.Drawing.SystemColors.Control)
objGraphics.DrawRectangle(System.Drawing.Pens.Blue, objPicturebox.Left - 1, _
objPicturebox.Top - 1, _
objPicturebox.Width + 1, objPicturebox.Height + 1)
objGraphics.Dispose()
End Sub
Writing Code Procedures 223
FIGURE 10.4
Start your new
procedure where
the arrow is
pointing.
A few items introduced in this procedure may look new to you. The first is that there
is text within the parentheses of the procedure declaration. I mentioned earlier that
this is where you can define parameters. Parameters are data passed into the procedure,
as opposed to a value returned by the procedure. You’ve just created a parameter
of type picture box. I’ll cover the specifics in Hour 11, but for now I just want you
to understand the following concept: Code that calls this procedure passes into it a
reference to a picture box object. The procedure then can work with the reference just
as though it were manipulating the object directly.
The first procedure you created should have been done this way, but I wanted you to
see both approaches. In the first procedure (OpenPicture), you hard-coded a reference
to ViewerForm. This means that the code works for only that form. Because this
second procedure accepts a reference to a picture box by way of a parameter, the procedure
can work with a picture box on any form in your project. This is an important
concept to remember. You should strive to use parameters in your procedures while at
the same time avoiding hard-coding references to objects that belong to other forms.
The objPicturebox parameter is used throughout the procedure in place of a hardcoded
reference to the picture box object on your form. That’s pretty easy to understand,
but the second statement in the procedure needs a bit more clarification.
Notice the reference to objPicturebox.Parent. All controls have a parent, which is
the container on which the control is placed. The Parent property is an object property
that returns a reference to the parent. In the case of the picture box on your
form, Parent refers to the form itself. So, calling
224 HOUR 10: Creating and Calling Code Procedures
objPicturebox.Parent.CreateGraphics is the same as calling
picShowPicture.CreateGraphics or Me.CreateGraphics from within the form.
Your module should now look like Figure 10.5.
Declaring Procedures That Return Values
The two procedures you’ve created don’t return values. Now you’ll declare a
function—a procedure that returns a value. Here’s the general syntax of a function
declaration:
Scope Function functionname(parameters) As datatype
You’ll notice two key differences between declaring a procedure that doesn’t return a
value and declaring one that does. First, you use the keyword Function in place of
the keyword Sub. Second, you add text after the parentheses. When declaring a function,
you’ll always enter two words after the parentheses. The first word is always As,
and the second word is a specific data type declaration. Data types are discussed in
detail in Hour 11, so it’s not important that you understand them now. It is important,
however, that you understand what’s happening.
As stated previously, functions return values. The data type entered after As denotes
the type of data the function returns. You won’t create a Function in your project at
this time, but consider the following sample Function:
Public Function ComputeLength(ByVal strText As String) As Integer
FIGURE 10.5
Code must exist
within procedures,
and procedures
must be
placed between
the Module declaration
and End
Module.
Calling Code Procedures 225
Return strText.Length
End Function
Note three things here:
. After the parentheses are the words As Integer. This denotes that the
Function returns an Integer. If the function were to return a string of text, it
would be declared As String. It’s important that you declare the proper data
type for your functions, as discussed in Hour 11.
. The keyword Return accomplishes two tasks. First, it causes the procedure to
terminate immediately—no further code is executed in the procedure. Second, it
passes back as the return value whatever you specify. In this code, the
Function returns the number of characters in the supplied string.
. Notice that instead of End Sub, End Function is used to denote the end of the
procedure. This behavior keeps the End statements consistent with their corresponding
declaration statements.
Sub and Function procedures are similar—short of these three things. By remembering
these key differences, you should have little trouble creating one over the other as
circumstances dictate.
Calling Code Procedures
Calling a procedure is simple—much simpler than creating one! So far, I’ve had you
create two procedures. Each of these procedures contains code like that used in no less
than three places! Now you’ll remove all that duplicate code, replacing it with calls to
the common procedures you’ve just written. Follow these steps to make this happen:
1. Double-click ViewerForm.vb in the Solution Explorer to view the form in the
Form Designer.
2. The first code you’ll replace is the Open Picture code you entered for the Open
Picture button on the toolbar. Double-click the Open Picture button to access its
Click event. Delete all the code between the event declaration and End Sub, as
shown in Figure 10.6.
3. With the old code deleted, enter the following statement:
OpenPicture()
That’s it! To call a Sub procedure (a procedure that doesn’t return a value), you
simply use the procedure name followed by a pair of parentheses. If the procedure
expects one or more parameters, you would enter them between the
parentheses.
226 HOUR 10: Creating and Calling Code Procedures
FIGURE 10.6
Delete this code
and replace it
with the procedure
call.
When you type in the name of a valid procedure and then the left parenthesis,
Visual Basic displays a ToolTip showing the parameters that the procedure
expects. It can be difficult to remember the parameters expected by all procedures
(not to mention the proper order in which to pass them), so this little feature
will save you a great deal of time and frustration.
Did you
Know?
4. We still have two other places in which we used the Open Picture code. Doubleclick
ViewerForm.vb in the Solution Explorer to return to the form’s design view,
click the File menu to display the menu, and then double-click the Open Picture
button.
5. Delete the code in the Click event and replace it with the following:
OpenPicture()
Return to the Form Designer.
So far, you’ve created only Sub procedures—procedures that don’t return values. As
you now know, calling a Sub procedure is as easy as referencing the Sub’s name and
its parentheses. Calling Function procedures—those that return values—is a bit different.
Consider this little function:
Public Function AddTwoNumbers(ByVal intFirst As Integer, _
ByVal intSecond As Integer) As Long
Return intFirst + intSecond
End Function
Calling Code Procedures 227
This function accepts two parameters, adds them together, and returns their sum.
When calling a Function, think of the function in terms of the value it returns. For
example, when you set a form’s Height property, you set it with code like this:
MyForm.Height = 200
This statement sets a form’s height to 200. Suppose that you want to use the
AddTwoNumbers procedure to determine the form’s Height. Thinking of the procedure
in terms of the value it returns, you could replace the literal value with the function,
as in the following:
MyForm.Height = AddTwoNumbers(1, 5)
In this example, the form’s height is set to 6, because you pass 1 and 5 to the function’s
parameters, and the function adds them together. In the next section, I show
you how to work with parameters in more detail.
When calling Function procedures, you must treat the procedure call as you
would treat the literal value returned by the function. This often means placing a
function call on the right side of an equals sign or embedding it in an expression.
By the
Way
You’ve now created a procedure and called it from two locations—your application is
really taking shape! Now that you have a toolbar and a menu, you no longer need
the buttons that you created in Hour 1, “Jumping in with Both Feet: A Visual Basic
2010 Programming Tour.”
Follow these steps to get rid of the buttons:
1. Double-click the Select Picture button on the right side of the form. Remove the
entire event, including the procedure declaration that begins with Private,
and the End Sub statement, as shown in Figure 10.7.
2. Go back to the Form Designer by clicking the ViewerForm.vb[Design]* tab at
the top of the work area.
3. The Select Picture button should be selected, because you just double-clicked it.
If it is not, click it to select it. Press Delete to delete the button.
4. Repeat steps 1 through 3 for the Quit button, the Draw Border button, and the
Options button. Be sure to delete the procedures for each of them! Your screen
should now look like Figure 10.8.
5. Go ahead and clean up the form further. Set the Location property of the X
label to 336, 256, and set the Location property of the Y label to 336, 269.
228 HOUR 10: Creating and Calling Code Procedures
FIGURE 10.7
When deleting a
procedure, you
must delete the
declaration and
the End statement
as well.
FIGURE 10.8
The buttons are
no longer necessary
now that
you have menus
and toolbars.
Finally, set the Size of the Picture box to 322, 257. Now your form should look
like Figure 10.9.
Passing Parameters
Parameters are used within a procedure to allow the calling code to pass data into the
procedure. You’ve already seen how parameters are defined: within the parentheses
Calling Code Procedures 229
FIGURE 10.9
Much better!
of a procedure declaration. A parameter definition consists of a name for the parameter,
the word As, and a data type:
Public Sub MyProcedure(strMyStringParameter As String)
After you’ve read about variables in Hour 11, this structure will make much more
sense. Here, I just want you to get the general idea of how to define and use
parameters.
By the
Way
You can define multiple parameters for a procedure by separating them with a
comma, like this:
Public Sub MyProcedure(strMyStringParameter As String, _
intMyIntegerParameter as Integer)
A calling procedure passes data to the parameters by way of arguments. This is mostly
a semantics issue; when defined in the declaration of a procedure, the item is called a
parameter. When the item is part of the statement that calls the procedure, it’s called
an argument. Arguments are passed within parentheses—the same way that parameters
are defined. If a procedure has multiple arguments, you separate them with
commas. For example, you could pass values to the procedure just defined by using a
statement such as this:
MyProcedure(“This is a string”, 11)
The parameter acts like an ordinary variable within the procedure. Remember, variables
are storage entities whose values can be changed. The statement just shown sends
literal values to the procedure. You could also send the values of variables this way:
MyProcedure(strAString, intAnInteger)
230 HOUR 10: Creating and Calling Code Procedures
An important thing to note about passing variables in Visual Basic is that parameters
are passed by value rather than by reference. When parameters are passed by value,
the procedure receives a copy of the data; changes to the parameter do not affect the
value of the original variable. When passed by reference, however, the parameter is
actually a pointer to the original variable. Changes made to the parameter within
the procedure propagate to the original variable. To pass a parameter by reference,
you preface the parameter definition with the keyword ByRef, as shown here:
Public Sub MyProcedure(ByRef strMyStringParameter As String, _
intMyIntegerParameter as Integer)
Parameters defined without ByRef are passed by value—this is the default behavior
of parameters in Visual Basic. Therefore, in this declaration, the first parameter is
passed by reference, whereas the second parameter is passed by value. Actually, if
you typed in this statement, Visual Basic would automatically add ByVal in front of
intMyIntegerParameter for you.
The default behavior in earlier versions of Visual Basic was that parameters were
passed by reference, not by value. To pass a parameter by value, you had to preface
the parameter definition with ByVal.
By the
Way
You already created a procedure that accepts a parameter. Let’s take another look:
Public Sub DrawBorder(ByRef objPicturebox As PictureBox)
Dim objGraphics As Graphics
objGraphics = objPicturebox.Parent.CreateGraphics
objGraphics.Clear(System.Drawing.SystemColors.Control)
objGraphics.DrawRectangle(System.Drawing.Pens.Blue, objPicturebox.Left - 1, _
objPicturebox.Top - 1, _
objPicturebox.Width + 1, objPicturebox.Height + 1)
objGraphics.Dispose()
End Sub
Notice that the parameter is declared with ByRef. That’s because you’re not passing
some ordinary piece of data, like a number or a string of text. This procedure accepts
an object—a picture box, to be exact. Within the procedure, you reference properties
of the picture box. For this to take place, the variable must be by reference (you need
a pointer to the actual object to reference its properties and methods). Follow these
steps to hook up the procedure:
1. Display the ViewerForm form in the Form Designer.
2. Double-click the Draw Border button on the toolbar. Delete the contents of the
procedure, but not the procedure shell (the first statement, starting with
Private, and the last statement, End Sub).
Exiting Procedures 231
3. Enter the following statement in the Click event:
DrawBorder(picShowPicture)
4. Return to the Form Designer once more (you should know how by now), click
the Tools menu on your form, and then double-click the Draw Border item.
5. Replace all the code within the procedure with this statement:
DrawBorder(picShowPicture)
You’ve now hooked up your menus and Toolstrip. Press F5 to run your program (see
Figure 10.10), and try the various menu items and tool buttons. The Confirm on Exit
button still doesn’t work, but you’ll hook that up in the next hour.
Go ahead and stop the running project, and save your work.
Exiting Procedures
Code within a procedure ordinarily executes from beginning to end—literally. When
an End Sub or End Function statement is reached, execution returns to the statement
that made the procedure call. You can force execution to leave the procedure at
any time by using an Exit Sub or Exit Function statement. Obviously, you use
Exit Sub in procedures declared with the keyword Sub, and you use Exit Function
in procedures declared with the keyword Function. If Visual Basic encounters such an
FIGURE 10.10
Professional
applications
demand good
procedure
design in addition
to good
interface
design.
232 HOUR 10: Creating and Calling Code Procedures
exit statement, the procedure terminates immediately, and code returns to the statement
that called the procedure. Take care to minimize the number of Exit statements
in any given routine. By providing too many exit points in a procedure, you will
make your code difficult to read and harder to debug.
Avoiding Infinite Recursion
It’s possible to call procedures in such a way that a continuous loop occurs. Consider
the following two procedures:
Public Sub DoSomething()
Call DoSomethingElse()
End Function
Public Sub DoSomethingElse()
Call DoSomething()
End Function
Calling either of these procedures produces an infinite loop of procedure calls and
results in the error shown in Figure 10.11.
This endless loop is known as a recursive loop. Without getting too technical, Visual
Basic allocates some memory for each procedure call in an area known as the stack.
Only a finite amount of space is available on the stack, so infinite recursion eventually
uses all the available stack space, and an exception occurs. This is a serious error,
and steps should be taken to avoid such recursion.
FIGURE 10.11
Infinite recursion
results in a
stack overflow
exception
(error).
Q&A 233
Legitimate uses exist for recursion, most notably in the use of algorithms such as
those used in calculus or those used to iterate through all the folders on a hard drive.
Deliberate recursion techniques don’t create infinite recursion, however; there is
always a point at which the recursion stops (hopefully, before the stack is consumed).
If you have an interest in such algorithms, consider reading a book dedicated to the
subject.
Summary
In this hour, you learned how a procedure is a discrete set of code designed to perform
a task or related set of tasks. Procedures are where you write Visual Basic code. Some
procedures might be as short as a single line of code, whereas others will be pages in
length. You learned how to define procedures and how to call them; creating and
calling procedures is critical to your success in programming with Visual Basic. Be
sure to avoid creating recursive procedures! You’ll use procedures so often that they’ll
become second nature to you in no time.
Modules are used to group related procedures. This hour focused on the standard
module, which is little more than a container for procedures. Remember to group
related procedures in the same module and to give each module a descriptive name.
In Hour 16, you’ll build on your experience with modules and work with class modules,
which demands good segregation of discrete modules.
Keep in mind that every procedure should perform a specific function. Therefore,
you should avoid creating procedures that perform many different tasks. For
example, suppose that you want to create a set of code that draws an ellipse on
a form. You also want to clear the form. If you placed both sets of code in the
same procedure, the ellipse would be drawn and then immediately erased. By
placing each set of code in its own procedure, you can draw the ellipse by calling
one procedure and then erase it at any time by calling the other procedure. By
placing these routines in a module rather than attaching them to a specific form,
you also make the procedures available to any form that needs them.
Did you
Know?
Q&A
Q. Do I need to pay much attention to scope when defining my procedures?
A. It might be tempting to create all your procedures as Public, but this is bad
coding practice for a number of reasons. For one thing, you’ll find that in
larger projects, you have procedures with the same name that do slightly different
things. Usually, these routines are relevant only within a limited scope.
However, if you create all Public procedures, you’ll run into conflicts when
234 HOUR 10: Creating and Calling Code Procedures
you create a procedure with the same name in the same scope. If the procedure
isn’t needed at the Public level, don’t define it for public access.
Q. How many modules is a reasonable number?
A. That’s hard to say. In my largest application (which is a very large application),
I have had about 18 modules, but I have been reducing them over time
by replacing them with class modules. Anything greater than that and the
project might become difficult to manage.
Workshop
Quiz
1. What are the entities called that are used to house procedures?
2. True or false: To access procedures in a class module, you must first create an
object.
3. To declare a procedure that returns a value, do you use Sub or Function?
4. True or false: You use a Call statement to call a procedure that returns a value.
5. Data that has been passed into a procedure by a calling statement is called what?
6. To pass multiple arguments to a procedure, with what do you separate them?
7. The situation in which a procedure or set of procedures continues to call each
other in a looping fashion is called what?
Workshop 235
Answers
1. Modules
2. True
3. Functions return values.
4. False. Older versions of Visual Basic had you use the word Call to call Sub procedures,
but this is no longer necessary. Call was never used for Functions.
5. A parameter
6. A comma (,)
7. Infinite recursion
Exercises
1. Create a procedure as part of a form that accepts one string and outputs a different
string. Add code to the TextChanged event of a text box to call the procedure,
passing the contents of the text box as the argument. Pass back as the
result of the procedure the uppercase version of the string passed into it. (Hint:
Use the Visual Basic UCase() function.)
2. Create a single procedure that calls itself. Call this procedure from the Click
event of a button and observe the resulting error.
This page intentionally left blank
237
HOUR 11
Using Constants, Data
Types, Variables, and Arrays
What You’ll Learn in This Hour:
. Understanding data types
. Determining data type
. Converting data to different data types
. Defining and using constants
. Dimensioning and referencing variables
. Understanding explicit variable declaration and strict typing
. Working with arrays
. Determining scope
. Declaring static variables
. Using a naming convention
As you write your Visual Basic procedures, you’ll regularly need to store and retrieve
various pieces of information. As a matter of fact, I can’t think of a single application
I’ve written that didn’t need to store and retrieve data in code. You might want
to keep track of how many times a procedure has been called, for example, or store a
property value and use it later. Such data can be stored as constants, variables, or
arrays. Constants are named values that you define at design time. Constants cannot
be changed after that, but they can be referenced as often as needed. Variables, on
the other hand, are like storage bins; you can retrieve or replace the data in a variable
as often as you need to. Arrays act like grouped variables, enabling you to store
many values in a single array variable.
Whenever you define one of these storage entities, you have to decide what type of
data it will contain. For example, will the new variable hold a string value (text) or a
238 HOUR 11: Using Constants, Data Types, Variables, and Arrays
number? If it will hold a number, is the number a whole number, an integer, or
something else entirely? After you determine the type of data to store, you must
choose the level of visibility that the data has to other procedures within the project
(this visibility is known as scope). In this hour, you’ll learn the ins and outs of Visual
Basic data types. (If you’re moving up from Visual Basic 6, you’ll note that even
though some data types share the same names, they are different.) You’ll also learn
how to create and use these storage mechanisms and how to minimize problems in
your code by reducing scope.
In this hour, you’ll build on the Picture Viewer project from Hour 10, “Creating and
Calling Code Procedures.” Here, you’ll start the process for hooking up the features
for which you created controls on your Options form.
By the
Way
Understanding Data Types
Every programming language has a compiler. The compiler is the part of the Visual
Studio .NET Framework that interprets the code you write into a language the computer
can understand. The compiler must understand the type of data you’re manipulating
in code. For example, if you asked the compiler to add the following values,
it would get confused:
“Fender Strat” + 63
When the compiler gets confused, either it refuses to compile the code (which is the
preferred situation, because you can address the problem before your users run the
application), or it halts execution and displays an exception (error) when it reaches
the confusing line of code. (These two types of errors are discussed in detail in Hour
15, “Debugging Your Code.”) Obviously, you can’t add the words “Fender Strat” to
the number 63, because these two values are different types of data. In Visual Basic,
these two values are said to have two different data types. Constants, variables, and
arrays must always be defined to hold a specific type of information.
Determining Data Type
Data typing—the act of defining a constant, variable, or array’s data type—can be
confusing. To Visual Basic, a number is not just a number. A number that contains a
decimal value is different from a number that doesn’t. Visual Basic can perform
arithmetic on numbers of different data types, but you can’t store data of one type in
Understanding Data Types 239
a variable with an incompatible type. Because of this limitation, you must give careful
consideration to the type of data you plan to store in a constant, variable, or
array when you define it. Table 11.1 lists the Visual Basic data types and the range of
values each one can contain.
TABLE 11.1 Visual Basic Data Types
Data Type Value Range
Boolean True or False
Byte 0 to 255 (unsigned)
Char A single Unicode character
Date 0:00:00 (midnight) on January 1, 0001, through 11:59:59 p.m. on
December 31, 9999
Decimal 0 through +/79,228,162,514,264,337,593,543,950,335, with no
decimal point; +/–7.9228162514264337593543950335, with 28
places to the right of the decimal. Use this data type for currency
values.
Double –1.79769313486231570E+308 through –4.94065645841246544E-
324 for negative values; 4.94065645841246544E-324 through
1.79769313486231570E+308 for positive values
Integer –2,147,483,648 to 2,147,483,647 (signed). This is the same as the
data type Int32.
Long –9, 223,372,036,854,775,808 to 9,223,372,036,854,775,807
(signed). This is the same as data type Int64.
Object Any type can be stored in a variable of type Object.
SByte -128 through 127 (signed)
Short –32,768 to 32,767 (signed). This is the same as data type Int16.
Single –3.4028235E+38 through –1.401298E-45 for negative values;
1.401298E-45 through 3.4028235E+38 for positive values
String 0 to approximately 2 billion Unicode characters
UInteger 0 through 4,294,967,295 (unsigned)
ULong 0 through 18,446,744,073,709,551,615 (1.8...E+19) (unsigned)
UShort 0 through 65,535 (unsigned)
240 HOUR 11: Using Constants, Data Types, Variables, and Arrays
The list of data types might seem daunting at first, but you can follow some general
guidelines for choosing among them. As you become more familiar with the
different types, you’ll be able to fine-tune your data type selection.
Following are some helpful guidelines for using data types:
. If you want to store text, use the String data type. The String data type
can be used to store any valid keyboard character, including numbers and
non-alphabetic characters.
. To store only the value True or False, use the Boolean data type.
. If you want to store a number that doesn’t contain decimal places and is
greater than –32,768 and smaller than 32,767, use the Short data type.
. To store numbers without decimal places, but with values larger or smaller
than Short allows, use the Integer or Long (an abbreviation for “long integer”)
data types.
. If you need to store numbers that contain decimal places, use the Single
data type. The Single data type should work for almost all values containing
decimals, unless you’re writing incredibly complex mathematical applications
or need to store very large numbers. In that case, use a Double.
. To store currency amounts, use the Decimal data type.
. If you need to store a date and/or a time value, use the Date data type.
When you use the Date data type, Visual Basic recognizes common date and
time formats. For example, if you store the value 7/22/2012, Visual Basic
doesn’t treat it as a simple text string; it knows that the text represents July
22, 2012.
. Different data types use different amounts of memory. To preserve system
resources, it’s best to use the data type that consumes the least amount of
memory and still enables you to store the full range of possible values. For
example, if you’re storing only the numbers from 1 to 10, use a Short
instead of a Long.
The Object data type requires special attention. If you define a variable or array
as an Object data type, you can store just about any value you care to in it;
Visual Basic determines what data type to use when you set the variable’s value.
Using Object data types has several drawbacks. First, Object data types take up
more memory than the other data types. In addition, Visual Basic takes a little
longer to perform calculations on Object data types. Unless you have a specific
reason to do so—and there are valid reasons, such as when you don’t know the
type of data to be stored ahead of time—don’t use the Object data type.
Instead, become familiar with the explicit data types and use them appropriately.
By the
Way
Understanding Data Types 241
Casting Data from One Data Type to Another
Under most circumstances, Visual Basic won’t allow you to move data of one type
into a variable of another type. The process of changing a value’s data type is known
as casting. Casting to a data type that holds a larger value or that has greater precision
is called casting upward. Casting to a data type that holds a smaller value or that
has less precision is known as casting downward. Visual Basic generally casts downward
but not upward. For instance, you can set the value of a variable declared as
Double to the value of a variable declared as Single without an explicit cast because
there’s no risk of losing data—Double holds more than Single. However, you can’t
set a variable declared as Single to the value of a variable declared as Double without
explicitly casting the type by using a data type conversion function. Visual Basic
makes you explicitly convert a Single to a Double because you run the risk of losing
data when doing so.
Table 11.2 lists the type conversion functions you can use to cast data to a different
type (think of C as standing for cast). The use of these functions is pretty straightforward:
Pass the data to be cast as the parameter, and the function returns the value
with the return type. For example, to place the value of a variable declared as Double
into a variable declared as Single, you could use a statement such as the following:
sngVariable = CSng(dblVariable)
TABLE 11.2 Type Conversion Functions
Function What It Converts To
CBool(expression) Boolean
CByte(expression) Byte
CChar(expression) Char
CDate(expression) Date
CDbl(expression) Double
CDec(expression) Decimal
CInt(expression) Integer
CLng(expression) Long
CObj(expression) Object
CSByte(expression) SByte
CShort(expression) Short
242 HOUR 11: Using Constants, Data Types, Variables, and Arrays
A Boolean value holds only True or False. However, it’s important to understand
how Visual Basic works with Boolean values under the hood. In Visual Basic,
True is stored internally as –1 (negative 1), whereas False is stored as 0. Actually,
any nonzero number can represent True, but Visual Basic always treats True
internally as –1. When casting a numeric value to a Boolean, Visual Basic casts a
value of 0 as False and casts any nonzero number as True. This becomes important
when you start evaluating numeric values using Boolean logic (discussed in
Hour 12, “Performing Arithmetic, String Manipulation, and Date/Time Adjustments”).
By the
Way
Defining and Using Constants
When you hard-code numbers in your procedures (such as in intVotingAge = 18), a
myriad of things can go wrong. Hard-coded numbers often are called magic numbers
because they’re usually shrouded in mystery. The meaning of such a number is
obscure because the digits themselves don’t indicate what the number represents.
Constants are used to eliminate the problems of magic numbers.
You define a constant as having a specific value at design time, and that value never
changes throughout the life of your program. Constants offer the following benefits:
. They eliminate or reduce data-entry problems: It’s much easier to remember
to use a constant named c_pi than it is to enter 3.14159265358979 everywhere
that pi is needed. The compiler catches misspelled or undeclared constants, but
it doesn’t care one bit what you enter as a literal value.
. Code is easier to update: If you hard-coded a mortgage interest rate at 6.785,
and the rate changed to 7.00, you’d have to change every occurrence of 6.785
in code. In addition to the possibility of data-entry problems, you’d run the risk
TABLE 11.2 Continued
CSng(expression) Single
CStr(expression) String
CUInt(expression) UInteger
CULng(expression) ULong
CUShort (expression) UShort
Defining and Using Constants 243
of changing a value of 6.785 that had nothing to do with the interest rate—perhaps
a value that represented a savings bond yield (okay, a very high savings
bond yield). With a constant, you change the value once at the constant declaration,
and all code that references the constant uses the new value right away.
. Code is easier to read: Magic numbers are often anything but intuitive. Wellnamed
constants, on the other hand, add clarity to code. For example, which of
the following statements makes more sense to you?
decInterestAmount = CDec((decLoanAmount * 0.075) * 12)
or
decInterestAmount = CDec((decLoanAmount * c_sngInterestRate) * _
c_intMonthsInTerm)
Constant definitions have the following syntax:
Const name As datatype = value
To define a constant to hold the value of pi, for example, you could use a statement
such as this:
Const c_pi As Single = 3.14159265358979
Note how I prefix the constant name with c_. I do this so that it’s easier to determine
what’s a variable and what’s a constant when reading code. See the “Naming Conventions”
section later in this hour for more information.
After a constant is defined, you can use its name in code in place of its value. For
example, to output the result of 2 times the value of pi, you could use a statement
like this (the * character is used for multiplication and is covered in Hour 12):
Debug.WriteLine(c_pi * 2)
Using the constant is much easier and less prone to error than typing this:
Debug.WriteLine(3.14159265358979 * 2)
Constants can be referenced only in the scope in which they are defined. I discuss
scope in the section “Determining Scope” later in this hour.
You’ll use what you learn in this hour to enable the options controls that you added
in Hour 7, “Working with Traditional Controls.” The first thing you’ll do is use constants
to create default values for the options. Recall from Hour 7 that you created an
option form that allowed the user to manipulate the following three options:
. The user’s name: This is displayed in the Picture Viewer’s main form title bar.
244 HOUR 11: Using Constants, Data Types, Variables, and Arrays
. Prompt to confirm on exit: This is used to determine whether the user is asked
whether he or she really wants to shut down the Picture Viewer application.
. The default background color of the picture box: This can be set to gray (the
default) or white.
In the following steps, you’ll create a constant for the default value of the Prompt on
Exit option. Start by opening the Picture Viewer project from Hour 10, and then follow
these steps:
1. Click ViewerForm.vb in the Solution Explorer to select it.
2. Click the View Code button at the top of the Solution Explorer to view the code
behind ViewerForm.vb.
3. The constants you are about to create will be module-level constants. That is,
they can be used anywhere within the module in which they are declared. This
means that they won’t be placed in a specific procedure. The place to put module
constants is right after the declaration of the module toward the top
(Public Class classname). Position the cursor on the line following the declaration,
press Enter to create a new line, and then enter the following constant
declaration (see Figure 11.1):
Const c_defPromptOnExit = False
In the next section, you’ll learn how to use this constant to set the value of a variable.
Declaring and Referencing Variables
Variables are similar to constants in that when you reference a variable’s name in
code, Visual Basic substitutes the variable’s value in place of the variable name during
code execution. This doesn’t happen at compile time, though, as it does with constants.
Instead, it happens at runtime—the moment the variable is referenced.
Variables, unlike constants, can have their values changed at any time.
Declaring Variables
The act of defining a variable is called declaring (sometimes dimensioning), which you
do most often by using the keyword Dim (short for dimension). (Variables with scope
other than local are dimensioned in a slightly different way, as discussed in the later
section “Determining Scope.”) You’ve already used the Dim statement in previous
hours, so the basic Dim statement should look familiar to you:
Declaring and Referencing Variables 245
FIGURE 11.1
Module constants
go here.
Dim variablename As datatype
It’s possible to declare multiple variables of the same type on a single line, as in
Dim I, J, K As Integer
However, this is often considered bad form because it tends to make the code
more difficult to read when strong variable names are used.
Did you
Know?
You don’t have to specify an initial value for a variable, although being able to do so
in the Dim statement is a useful feature of Visual Basic. To create a new String variable
and initialize it with a value, for example, you could use two statements like this:
Dim strBandName As String
strName = “Chemical Echo”
However, if you know the initial value of the variable at design time, you can include
it in the Dim statement, like this:
Dim strBandName As String = “Chemical Echo”
Note, however, that supplying an initial value doesn’t make this a constant; it’s still a
variable, and the value can be changed at any time. This method of creating an initial
value eliminates a code statement and makes the code a bit easier to read
because you don’t have to go looking to see where the variable is initialized.
246 HOUR 11: Using Constants, Data Types, Variables, and Arrays
It’s important to note that all data types have a default initial value. For the string
data type, this is the value Nothing. “Nothing” might sound odd; it’s essentially no
value—a string with no text. Empty strings are written in code as ””. For numeric
data types, the default value is 0; the output of the following statements would be 2:
Dim sngMyValue As Single
Debug.WriteLine (sngMyValue + 2)
You can’t use a reserved word to name a constant or a variable. For example, you
couldn’t use the word Sub or Public as a variable name. There is a master list of
reserved words, and you can find it by searching the Help text for “reserved keywords.”
You’ll naturally pick up most of the common ones because you’ll use
them so often. For others, the compiler tells you when something is a reserved
word. If you use a naming convention for your variables, which consists of giving
the variable names a prefix to denote their types, you’ll greatly reduce the chance
of running into reserved words.
By the
Way
Passing Literal Values to a Variable
The syntax of assigning a literal value (a hard-coded value such as 6 or “guitar”) to a
variable depends on the variable’s data type.
For strings, you must pass the value in quotation marks, like this:
strCollegeName = “Bellevue University”
For Date values (discussed in more detail in Hour 12), you enclose the value in # symbols,
like this:
dteBirthDate = #7/22/1969#
For numeric values, you don’t enclose the value in anything:
intAnswerToEverything = 42
Using Variables in Expressions
Variables can be used anywhere an expression is expected. The arithmetic functions,
for example, operate on expressions. You could add two literal numbers and store the
result in a variable like this:
intMyVariable = 2 + 5
In addition, you could replace either or both literal numbers with numeric variables
or constants, as shown here:
intMyVariable = intFirstValue + 5
intMyVariable = 2 + intSecondValue
intMyVariable = intFirstValue + intSecondValue
Declaring and Referencing Variables 247
Variables are a fantastic way to store values during code execution, and you’ll use
variables all the time—from performing decisions and creating loops to using them
as a temporary place to stick a value. Remember to use a constant when you know
the value at design time and the value won’t change. When you don’t know the
value ahead of time or the value might change, use a variable with a data type
appropriate to the variable’s function.
In Visual Basic, variables are created as objects. Feel free to create a variable
and explore its members (that is, the properties and methods). You do this by
entering the variable name and then a period (this works only after you’ve entered
the statement that declares the variable). For example, to determine the length of
the text within a string variable, you can use the Length property of a string variable
like this:
strMyVariable.Length
Some powerful features dangle off the data type objects.
Did you
Know?
Enforced Variable Declaration and Data Typing
By default, Visual Basic forces you to declare variables before you can use them. This
is called explicit variable declaration. In addition to this behavior, you can force Visual
Basic to strictly enforce data typing. Strict typing means that Visual Basic performs
widening conversions for you automatically if no data or precision is lost, but for
other conversions, you must explicitly cast the data from one type to another.
Explicit Variable Declaration
In the past, Visual Basic’s default behavior enabled you to create variables on the fly
(implicit variable declaration), and it didn’t even have a provision for enforcing strict
data typing. Although you can turn off both these features, you shouldn’t. In fact, I
recommend that you turn on Strict typing, which is off by default in new projects.
Take a look at the code following this paragraph now. No, really—right now. There’s a
problem with it, and I want you to see whether you can spot it. With Visual Basic’s
Option Explicit project property turned on, the following code would cause a compile
error because of the misspelling of the variable name on the MessageBox.Show()
statement. (Did you notice it?) When you turn off explicit variable declaration, Visual
Basic doesn’t check at compile time for such inconsistencies, and it would gladly run
this code:
Dim intMyVariable As Integer
intMyVariable = 10
MessageBox.Show(intMyVariabl)
248 HOUR 11: Using Constants, Data Types, Variables, and Arrays
Would an error occur at runtime? If not, what do you think would be displayed? 10?
No, nothing!
Notice that in the MessageBox.Show() statement, an e is missing from the
intMyVariable name. As Visual Basic compiles your code, it looks at each code entry
and attempts to determine whether it’s a keyword, function call, variable, constant,
or another entity that it understands. If the entry is determined to be something
Visual Basic knows nothing about, the default behavior is to generate a compile error.
With explicit variable declaration turned off (that is, the Option Explicit setting
turned off), however, Visual Basic alters this behavior. Instead, it creates a new variable—
of type Object, no less! As I stated earlier, all variables are initialized with
some default value. New object variables are empty, which is a value of sorts. Therefore,
nothing prints in this example, and no error occurs. You want to talk about
hard-to-find errors? This is one of the hardest I can come up with. If you’re tired and
it’s late, it could take you hours to notice that a variable name is misspelled (I’ve
been there—trust me). There is simply no valid reason to turn off explicit variable
declaration. Because Option Explicit is turned on for all new projects by default,
there’s really no reason to mess with this setting.
Strict Typing
Strict typing is the process by which Visual Basic enforces data typing; you can put a
value in a variable only if the value is of the correct data type. If you want to cast a
value of one type into a variable of another type that holds a smaller number or has
less precision, you must use a type-conversion function. With this feature turned off
(which it is for new projects by default), Visual Basic lets you move any type of data
into any variable, regardless of the data types involved. To do this, it has to make a
best guess about how the data should be cast, which can cause inaccuracies such as
truncating a large number when moving it from a Double to a Single. There are rare
circumstances in which you might need to turn off strict typing, but these only come
up with advanced programming. Leaving strict typing on forces you to write better
code, so I suggest that you turn it on in your projects. To turn on Option Strict in your
Picture Viewer project, follow these steps:
1. Right-click the project name in the Solution Explorer and choose Properties
from the context menu.
2. On the Project Properties page, click the Compile tab on the left.
3. Open the Option strict drop-down list and choose On, as shown in Figure 11.2.
4. While on the options page, change Option infer to Off.
Declaring and Referencing Variables 249
Press F5 to run your project. Visual Basic tells you that there was a build error, as
shown in Figure 11.3.
Follow these steps to correct it:
1. Click No to stop running the project and view the error.
2. Visual Basic returns to the code window, but a new window, the Error List, has
opened at the bottom (see Figure 11.4). Also notice that the constant you
declared now appears with a wavy blue underline (you’ll need to return to the
ViewerForm.vb tab to see the code) .
3. Notice the error message—it’s an accurate one. Visual Basic is telling you that it
wants to know the data type of every constant, variable, and array that you
create because you are using Option Strict. Your constant declaration doesn’t
FIGURE 11.2
Using Option
Strict forces you
to write better
code.
FIGURE 11.3
Simply enabling
Option Strict
broke the code.
250 HOUR 11: Using Constants, Data Types, Variables, and Arrays
FIGURE 11.4
The Error List
window helps
you pinpoint
problems in your
code.
include a data type, so Visual Basic doesn’t know how to handle this constant.
Double-click the error message to display the offending line of code, and then
change the constant declaration to look like this:
Const c_defPromptOnExit As Boolean = False
When you change the code, the Error List is cleared (go ahead and close the Error
List). What you did was specify a data type for the constant, so Visual Basic now
knows to always treat the constant value as a Boolean (true/false) value.
If you would have left Option Infer turned on, the code would still run without an
error. Option Infer tells Visual Basic to make a best guess at the data type based
on the value put into it. I recommend that you leave this option off, as it negates
the value of Option Explicit.
By the
Way
Working with Arrays
An array is a special type of variable—it’s a variable with multiple dimensions. Think
of an ordinary variable as a single mail slot. You can retrieve or change the contents
of the mail slot by referencing the variable. An array is like having an entire row of
mail slots (called elements). You can retrieve and set the contents of any of the indi-
Working with Arrays 251
vidual mail slots at any time by referencing the single array variable. You do this by
using an index that points to the appropriate slot.
Dimensioning Arrays
Arrays are dimensioned in much the same way as ordinary variables, with one
notable exception. Consider this statement:
Dim strMyArray(10) As String
This code is similar to the Dim statement of an ordinary String variable, with the difference
being the number 10 in parentheses. The number in parentheses determines
how many “mail slots” the array variable will contain, and it must be a literal value
or a constant—it can’t be another variable. The important point to remember is that
the number you specify isn’t the exact number of elements in the array—it’s 1 less, as
you’ll see.
It’s possible to create arrays that can be resized at runtime. However, this topic is
beyond the scope of this book.
By the
Way
Referencing Array Variables
To place a value in an array index, you specify the index number when referencing
the variable. Most computer operations consider 0 to be the first value in a series, not
1, as you might expect. This is how array indexing behaves. For example, for an
array dimensioned with 10 elements—declared using (9)—you would reference the
elements sequentially by using the indexes 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9.
Notice that the upper index is the number specified when the array was declared.
Because 0 is a valid element, you end up with 1 more than the number you used
to declare the array. This can be confusing. To simplify your development, you
might consider just ignoring element 0 and using elements 1 through the
declared upper value.
By the
Way
To place a value in the first element of the array variable, you would use 0 as the
index, like this:
strMyArray(0) = “This value goes in the first element”
To reference the second element, you could use a statement like this:
strMyVariable = strMyArray(1)
252 HOUR 11: Using Constants, Data Types, Variables, and Arrays
The data type specified for the array variable is used for all the elements in the
array. You can use the Object type to hold any type of data in any element, but
doing so isn’t recommended for all the reasons discussed earlier.
By the
Way
Creating Multidimensional Arrays
Array variables require only one declaration, yet they can store numerous pieces of
data; this makes them perfect for storing sets of related information. The array example
shown previously is a single-dimension array. Arrays can be much more complex
than this example and can have multiple dimensions of data. For example, a single
array variable could be defined to store personal information for different people. Multidimensional
arrays are declared with multiple parameters, such as the following:
Dim intMeasurements(3,2) as Integer
This Dim statement creates a two-dimensional array. The first dimension (defined as
having four elements: 0, 1, 2, and 3) serves as an index to the second dimension
(defined as having three elements: 0, 1, and 2). Suppose that you want to store the
height and weight of three people in this array. You reference the array as you would
a single-dimension array, but you include the extra parameter index. The two
indexes together specify an element, much like coordinates in the game Battleship
relate to specific spots on the game board. Figure 11.5 illustrates how the elements
are related.
Single Dimension Array
Single Dimension
0 1 2 3 4 5 6 7
Two Dimensional Array
First Dimension
0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0
0,1 1,1 2,1 3,1 4,1 5,1 6,1 7,1
0,2 1,2 2,2 3,2 4,2 5,2 6,2 7,2
0,3 1,3 2,3 3,3 4,3 5,3 6,3 7,3
Second Dimension
FIGURE 11.5
Two-dimensional
arrays are like a
wall of mail
slots.
Working with Arrays 253
Elements are grouped according to the first index specified; think of the first set of
indexes as being a single-dimension array. For example, to store the height and
weight of a person in the array’s first dimension (remember, arrays are 0-based), you
could use code such as the following:
intMeasurements(0,0) = FirstPersonsHeight
intMeasurements(0,1) = FirstPersonsWeight
I find it helpful to create constants for the array elements, which makes array references
much easier to understand. Consider this:
Const c_Height As Integer = 0
Const c_Weight As Integer = 1
intMeasurements(0, c_Height) = FirstPersonsHeight
intMeasurements(0, c_Weight) = FirstPersonsWeight
You could then store the height and weight of the second and third person like this:
intMeasurements(1, c_Height) = SecondPersonsHeight
intMeasurements(1, c_Weight) = SecondPersonsWeight
intMeasurements(2, c_Height) = ThirdPersonsHeight
intMeasurements(2, c_Weight) = ThirdPersonsWeight
In this array, I’ve used the first dimension to differentiate people. I’ve used the second
dimension to store a height and weight for each element in the first dimension.
Because I’ve consistently stored heights in the first slot of the array’s second dimension
and weights in the second slot of the array’s second dimension, it becomes easy
to work with these pieces of data. For example, you can retrieve the height and
weight of a single person as long as you know the first dimension index used to store
the data. You could write the total weight of all three people to the Output window
using the following code:
Debug.WriteLine(intMeasurements (0, c_Weight) + _
intMeasurements(1, c_Weight) + _
intMeasurements(2, c_Weight))
When working with arrays, keep the following points in mind:
. The first element in any dimension of an array has an index of 0.
. Dimension an array to hold only as much data as you intend to put in it.
. Dimension an array with a data type appropriate to the values to be placed in
the array’s elements.
Arrays are a great way to store and work with related sets of data in Visual Basic
code. Arrays can make working with larger sets of data much simpler and more efficient
than using other methods. To maximize your effectiveness with arrays, study
254 HOUR 11: Using Constants, Data Types, Variables, and Arrays
the For...Next loop discussed in Hour 14, “Looping for Efficiency.” Using a
For...Next loop, you can quickly iterate (loop sequentially) through all the elements
in an array.
Determining Scope
Constants, variables, and arrays are useful ways to store and retrieve data in Visual
Basic code. Hardly a program is written that doesn’t use at least one of these elements.
To properly use them, however, it’s critical that you understand scope.
You had your first encounter with scope in Hour 10, with the keywords Private and
Public. You learned that code is written in procedures and that procedures are stored
in modules. Scope refers to the level at which a constant, variable, array, or procedure
can be “seen” in code. For a constant or variable, scope can be one of the following:
. Block level
. Procedure level (local)
. Module level
. Global (also called namespace scope)
Scope has the same effect on array variables as it does on ordinary variables. For
the sake of clarity, I’ll reference variables in this discussion on scope, but understand
that what I discuss applies equally to arrays (and constants, for that matter).
By the
Way
Understanding Block Scope
Block scope, also called structure scope, is relatively new to Visual Basic .NET. Visual
Basic considers whether a variable is dimensioned within a structure. If it is, Visual
Basic gives the variable block scope.
Structures are coding constructs that consist of two statements, in contrast to one. For
example, you’ve already used If...Then decision structures in previous hours. Such
a structure looks like this:
If expression Then
statements to execute when expression is True
End If
The standard Do...Loop structure, which you’ll learn about in Hour 14, is used to
create a loop; it looks like this:
Do
statements to execute in the loop
Loop
Determining Scope 255
If a variable is declared within a structure, the variable’s scope is confined to the
structure; the variable isn’t created until the Dim statement occurs, and it’s destroyed
when the structure completes. If a variable is needed only within a structure, consider
declaring it in the structure to give it block scope. Consider the following example:
If blnCreateLoop Then
Dim intCounter As Integer
For intCounter = 1 to 100
‘ Do something
Next intCounter
End If
By placing the Dim statement within the If structure, you ensure that the variable is
created only if it’s needed. Variables consume resources, so if you only need a variable
under a specific condition, placing the Dim statement in a decision construct like an
If...End If block ensures that the resources are only used if necessary.
The various structures, including looping and decision-making structures, are discussed
in later hours.
By the
Way
Understanding Procedure-Level (Local) Scope
When you declare a constant or variable within a procedure, that constant or variable
has procedure-level or local scope. Most of the variables you’ll create will have procedure
scope. As a matter of fact, almost all the variables you’ve created in previous
hours have had procedure-level scope. You can reference a local constant or variable
within the same procedure, but it isn’t visible to other procedures. If you try to reference
a local constant or variable from a procedure other than the one in which it’s
defined, Visual Basic returns a compile error; to the procedure making the reference,
the variable or constant doesn’t exist. It’s generally considered a best practice to
declare all your local variables at the top of a procedure, but Visual Basic doesn’t care
where you place the Dim statements within the procedure. Note, however, that if you
place a Dim statement within a structure, the corresponding variable has block scope,
not local scope.
Understanding Module-Level Scope
When a constant or variable has module-level scope, it can be viewed by all procedures
within the module containing the declaration. To procedures in all other modules,
however, the constant or variable doesn’t exist. To create a constant or variable
with module-level scope, you must place the declaration within a module but not
256 HOUR 11: Using Constants, Data Types, Variables, and Arrays
within a procedure. There is a section for this—called the Declarations section—at the
top of each module (this is where you created your module-level constant earlier in
this hour). Use module-level scope when many procedures must share the same variable
and when passing the value as a parameter is not a workable solution.
Although module variables declared using Dim are private to the module, best
practice dictates that you use the Private keyword to declare private
module–level variables. That means it’s possible to create public module variables,
and you’ll learn about them in the next section.
By the
Way
For all modules other than those used to generate forms, it’s easy to add code to the
Declarations section; simply add the Public/Private statements just after the module
declaration line and before any procedure definitions, as shown in Figure 11.6.
A quick way to get to the Declarations section of any module is to choose (Declarations)
from the procedure drop-down list in the upper-right corner of a module
window.
Did you
Know?
Using Global (Namespace) Scope
A constant or variable is said to have global scope (or namespace scope) when it can be
seen and referenced from any procedure, regardless of the module in which the procedure
exists. One common use of a global variable is storing a reference to a database
connection so that all code that needs access to the database can do so via the vari-
FIGURE 11.6
The Declarations
section exists
above all
declared procedures.
Determining Scope 257
able. Creating global constants and variables is similar to declaring module-level
constants and variables. Global constants and variables must be declared in a module’s
Declarations section, just like module-level constants and variables. The difference
between a module-level declaration and a global-level declaration is the use of
the keyword Public. (You must observe some restrictions to create global variables
and constants; they’re discussed in the following section.)
To declare a global constant, begin the constant declaration with the word Public,
like this:
Public Const MyConstant As Integer = 1
To dimension a variable as a global variable, replace the keyword Dim or Private
with the word Public, like this:
Public strMyVariable as String
If Visual Basic gives you the compile error The name variablename is not
declared, first verify that you spelled the variable or constant reference correctly,
and then verify that the variable or constant you’re trying to reference is visible in
the current scope.
Did you
Know?
To create a constant or variable of global scope, you must declare the constant or
variable in a standard module, not a class-based module. If you declare a public variable
or constant in a class module (such as a Form class module), the variable or constant
behaves like a property of the class. This is a useful technique, and I discuss it in
Hour 16, “Designing Objects Using Classes.” Regardless, such a constant or variable
does not have global scope; it has module-level scope.
Scope Name Conflicts
You can’t have two variables of the same name in the same scope, but you can use
the same variable name for variables with different scope. For example, if you create
two public variables of the same name in standard modules (not class modules),
you’ve created two global variables with the same name. This causes a compile error
everywhere you attempt to access the variable. All variable references are ambiguous;
which one should Visual Basic use? You could, however, create a local variable with
the same name as a global variable (or even a module variable). Visual Basic always
uses the variable with the narrowest scope. Therefore, when referencing the variable
name in the procedure containing the local variable, Visual Basic would use the local
variable. When accessing the variable from another procedure, the local variable is
invisible, so the code would reference the global variable.
258 HOUR 11: Using Constants, Data Types, Variables, and Arrays
In general, the smaller (more limited) the scope, the better. When possible, make
your variables block or local variables. If you have to increase scope, attempt to
make the variable a module-level variable. Use global variables only when you
have no other options (and you usually have other options). The larger the scope,
the more the possibilities exist for problems, and the more difficult it is to debug
those problems. In general, when considering a global variable, attempt to wrap
the data in a class, as discussed in Hour 16.
Did you
Know?
Declaring Variables of Static Scope
When you create a variable within a procedure (local or block scope), the variable
exists only during the lifetime of the procedure or block (the scope of the variable).
When a variable goes out of scope, it’s destroyed, and whatever value was stored in
the old variable ceases to exist. The next time the procedure is called, Visual Basic
creates a new variable. Consider the following procedure:
Public Sub MyProcedure()
Dim intMyInteger As Integer
intMyInteger = intMyInteger + 10
End Sub
If you call this procedure, it creates a new variable called intMyInteger and sets its
value to its current value plus 10; then the procedure ends. Numeric variables have
an initial value of 0, so when End Sub is encountered in this example, the value of
intMyInteger is 10. When the procedure ends, the variable goes out of scope and
therefore is destroyed. If you were to call the procedure again, it would create a new
variable called intMyInteger (which again would default to 0) and increase its value
by 10. Again, the procedure would end, and the variable would be destroyed.
You can create variables that persist between procedure calls by using the keyword
Static. To create a static variable, use the keyword Static in place of the keyword
Dim. The following code is similar to the last example, except that the variable created
here is a static variable; it stays in existence and retains its value between calls
to the procedure in which it resides:
Public Sub MyProcedure()
Static intMyInteger As Integer
intMyInteger = intMyInteger + 10
End Sub
The first time this procedure is called, the variable intMyInteger is created with a
default value of 0, and then the variable is increased by 10. When the procedure
ends, the variable isn’t destroyed; instead, it persists in memory and retains its value
(because it’s declared with Static). The next time the procedure is called, Visual
Basic has no need to create a new variable, so the previous variable is used, and 10 is
Naming Conventions 259
By the
Way
TABLE 11.3 Prefixes for Common Data Types
Data Type Prefix Sample Value
Boolean bln blnLoggedIn
Byte byt bytAge
Char chr chrQuantity
Date dte dteBirthday
Decimal dec decSalary
Double dbl dblCalculatedResult
Integer int intLoopCounter
Long lng lngCustomerID
Object obj objWord
Short sho shoTotalParts
added to its value. The variable would have a value of 20 at the conclusion of the second
procedure call. Each subsequent call to the procedure would increase the value in
intMyInteger by 10.
Static variables aren’t nearly as common as ordinary variables, but they have their
uses. For one thing, static variables enable you to minimize scope (which is a good
thing). Why create a module-level variable when only one procedure will use it? As
you create your Visual Basic projects, keep static variables in mind. If you ever need
to create a variable that retains its value between calls, but whose scope is only procedure-
or block-level, you can do so by creating a static variable.
One scope identifier that I haven’t covered is Friend. When you declare a variable
or procedure by using Friend, it is given global scope within the project but
is not visible to applications that are accessing your code externally via Automation.
Because I don’t cover how to create Automation servers, I don’t have you
use Friend in your Picture Viewer project, but Visual Basic uses it often.
Naming Conventions
To make code more self-documenting (always an important goal) and to reduce the
chance of programming errors, you need an easy way to determine the exact data
type of a variable or the exact type of a referenced control in Visual Basic code.
Using Prefixes to Denote Data Type
Table 11.3 lists the prefixes of the common data types. Although you don’t have to
use prefixes, there are many advantages to doing so.
260 HOUR 11: Using Constants, Data Types, Variables, and Arrays
Denoting Scope Using Variable Prefixes
Not only are prefixes useful for denoting type, they also can be used to denote scope,
as shown in Table 11.4. In particularly large applications, a scope designator is a
necessity. Again, Visual Basic doesn’t care whether you use prefixes, but consistently
using prefixes benefits you as well as others who have to review your code.
Other Prefixes
Prefixes aren’t just for variables. All standard objects can use a three-character prefix.
There are simply too many controls and objects to list all the prefixes here,
although you’ll find that I use control prefixes throughout this book. If you’re interested
in learning more about naming conventions and coding standards in general, I
recommend that you take a look at my book Practical Standards for Microsoft Visual
Basic .NET, Second Edition (Microsoft Press, 2002).
TABLE 11.4 Prefixes for Variable Scope
Prefix Description Example
g_ Global g_strSavePath
m_ Module-level m_blnDataChanged
s_ Static variable s_blnInHere
No prefix Nonstatic variable, local to procedure
By the
Way
Did you
Know?
The prefix obj should be reserved for when a specific prefix is unavailable. The
most common use of this prefix is when referencing automation libraries of other
applications. For instance, when automating Microsoft Word, you create an
instance of Word’s Application object. Because there is no prefix specifically for
Word objects, obj works just fine. Here’s an example:
Dim objWord As Word.Application
You can hover the pointer over any variable in code and a ToolTip shows you the
variable’s declaration.
Using Variables in Your Picture Viewer Project 261
Using Variables in Your Picture Viewer
Project
You added a module-level constant to your Picture Viewer project earlier in this hour.
In this section, you’ll create variables to hold the values for the controls on your
Options form. In Hour 16, you will finish hooking up the options for your project.
Creating the Variables for the Options
In past hours, you defined three options for your Picture Viewer project. Let’s consider
each one now:
. User Name: This is where the user can enter her name, which appears in the
form’s title bar. Think for a moment about the type of data that will be stored
for this option. If you said String (which is text), you’re correct.
. Prompt to confirm on exit: This option has two possible values, true and
false, so you need to use a Boolean value to store this option.
. Default picture background color: This is actually a special case. I told you
about the common data types, but in addition to those there are dozens of
other different data types, one of which is Color. You’ll use a variable of the
data type Color to store the user’s background color preference.
Follow these steps to create the variables:
1. Display the code for the ViewerForm.vb form (not the OptionsForm.vb form).
2. Locate the Declarations section of the form’s module—it’s where you created
the constant c_defPromptOnExit.
3. Enter the following three variable declarations, beginning on the line following
the constant definition:
Private m_strUserName As String
Private m_blnPromptOnExit As Boolean
Private m_objPictureBackColor As Color
Your code should look like Figure 11.7.
262 HOUR 11: Using Constants, Data Types, Variables, and Arrays
Initializing and Using the Options Variables
Now that the variables have been created, you need to initialize them. Follow
these steps:
1. The best place to set up a form is usually in the form’s Load event. Getting to a
form’s events can be tricky. If you just select the form name in the object dropdown
box (the drop-down in the upper-left corner of the code window), you see
only a small subset of the form’s events. You need to open the object dropdown
and choose ViewerForm Events, as shown in Figure 11.8. After you’ve
chosen ViewerForm Events, open the event drop-down list and choose Load to
display the Load event.
FIGURE 11.7
Public variables
go in the Declarations
section.
Using Variables in Your Picture Viewer Project 263
FIGURE 11.8
You need to
choose this
option to see all
the form’s
events.
2. Your load event already has two lines of code: the two statements you entered
to set the value of the X and Y labels. Add the following two statements below
the existing code:
m_blnPromptOnExit = c_defPromptOnExit
m_objPictureBackColor = System.Drawing.SystemColors.Control
The first statement simply sets the module variable that stores the user’s
Prompt on Exit setting to the value of the constant you created earlier. I set up
the example this way so that you can see how constants and variables work
together. If you wanted to change the default behavior of the Close on Exit
option, all you would have to do is change the value of the constant in the
Declarations section.
The second statement sets the default back color to the default system color for
controls. I’ve already explained how this works in Hour 2, so I won’t go into
detail here. Notice that I did not create an initialization statement for the
module-level variable m_strUserName. This is because string variables are
initialized empty, which is exactly what we need at this time.
3. So far, you’ve created variables for the options and initialized them in code.
However, the option values aren’t actually used in the project yet. The Prompt
on Exit option is checked when the user closes the form, but the back color of
the picture box needs to be set before the form appears. Enter the following
264 HOUR 11: Using Constants, Data Types, Variables, and Arrays
statement right below the two you just created:
picShowPicture.BackColor = m_objPictureBackColor
All that’s left to do in this hour is to hook up the Prompt on Exit function. This
takes just a tad more work, because you created a menu item that keeps track
of whether the Prompt on Exit option is chosen. The first thing you’ll do is
make sure that the menu item is in sync with the variable; you don’t want the
menu item checked if the variable is set to False, because this would give the
opposite response from what the user expects. Continue with these steps to
hook up the Prompt on Exit variable.
4. Add this statement to your Form_Load event, right below the statement you
just entered to set the picture box’s back color. This statement ensures that
when the form loads, the checked state of the menu item matches the state of
the variable. Because Boolean variables initialize to False, the menu item
appears unchecked.
mnuConfirmOnExit.Checked = m_blnPromptOnExit
5. You already created a procedure for the menu item so that it physically
changes its Checked state when the user clicks it. You can scroll down the code
window and locate the procedure mnuConfirmOnExit_Click, or you can switch
to design view and double-click the menu item. Remember, there are usually
multiple ways to approach a problem in Visual Basic. After you’ve found the
procedure, add this statement below the existing code:
m_blnPromptOnExit = mnuConfirmOnExit.Checked
Did you notice that this statement is the exact opposite of the statement you
entered in step 4? You’ve just told Visual Basic to set the value of the variable
to the checked state of the menu item, after the checked state has been updated
in the Click event.
6. Now that the variable will stay in sync with the menu item, you need to hook
up the actual Prompt on Exit code. Open the object drop-down list and choose
ViewerForm Events again. In the event drop-down list, choose FormClosing.
Enter the following code exactly as it appears here:
If m_blnPromptOnExit Then
If MessageBox.Show(“Close the Picture Viewer program?”, _
“Picture Viewer”, MessageBoxButtons.YesNo, _
MessageBoxIcon.Question) = _
Windows.Forms.DialogResult.No Then
e.Cancel = True
End If
End If
Using Variables in Your Picture Viewer Project 265
I’ve already mentioned the MessageBox.Show() function (and I’ll explain it in detail
in Hour 17, “Interacting with Users”). All you need to understand here is that when
the user closes the Picture Viewer and the variable m_blnPromptOnExit is True, the
MessageBox.Show() function asks the user whether he or she really wants to quit. If
the user chooses No, the e.Cancel property is set to True, which cancels the form
from closing. (You can read more about the e object for the FormClosing event in the
online help text.)
Press F5 to run your project, and give it a try. When you first run the application, the
variable is False, and the menu item appears unchecked. If you click the Close button
in the upper-right corner of the form, the Picture Viewer closes. Run the project
again, but this time click the Confirm on Exit menu item to check it before you close
the form. This time, when you close the form, you are asked to confirm, as shown in
Figure 11.9.
FIGURE 11.9
It’s nice to give
the user control
over his or her
experience.
266 HOUR 11: Using Constants, Data Types, Variables, and Arrays
Summary
In this hour, you learned how to eliminate magic numbers by creating constants. By
using constants in place of literal values, you increase code readability, reduce the
possibility of coding errors, and make it much easier to change a value in the future.
In addition, you learned how to create variables for data elements in which the initial
value is unknown at design time, or for elements whose values will be changed
at runtime. You learned how arrays add dimensions to variables and how to declare
and reference them in your code.
Visual Basic enforces strict data typing, and in this hour you learned about the various
data types and how they’re used, as well as tips for choosing data types and
functions for converting data from one type to another. Finally, you learned about
scope—an important programming concept—and how to manage scope within your
projects.
Writing code that can be clearly understood by those who didn’t write it is a worthwhile
goal. Naming prefixes goes a long way toward accomplishing this goal. In this
hour, you learned the naming prefixes for the common data types, and you learned
how to use prefixes to denote scope.
In the end, you utilized all these concepts and created a constant and some variables
to handle the options of your Picture Viewer program. You even added code to make
them work! The Options form is still not hooked up, but you’ll fix that in Hour 16.
Q&A
Q. Are any performance tricks related to the many data types?
A. One trick when using whole numbers (values with no decimal places) is to use
the data type that matches your processor. For instance, most current home
and office computers have 32-bit processors. The Visual Basic Integer data
type is made up of 32 bits. Believe it or not, Visual Basic can process an
Integer variable faster than it can process a Short variable, even though the
Short variable is smaller. This has to do with the architecture of the CPU,
memory, and bus. The explanation is complicated, but the end result is that
you should usually use Integer rather than Short, even when working with
values that don’t require the larger size of the Integer.
Workshop 267
Q. Are arrays limited to two dimensions?
A. Although I showed only two dimensions, such as intMeasurements(3,1), arrays
can have many dimensions, such as intMeasurements(3,3,3,4). The technical
maximum is 32 dimensions, but you probably won’t use more than three.
Workshop
Quiz
1. What data type would you use to hold currency values?
2. Which data type can be used to hold any kind of data and essentially serves as
a generic data type?
3. What numeric values does Visual Basic internally equate to True and False?
4. What can you create to eliminate magic numbers by defining a literal value in
one place?
5. What type of data element can you create in code that can have its value
changed as many times as necessary?
6. What are the first and last indexes of an array dimensioned using Dim
a_strMyArray(5) As String?
7. What term describes the visibility of a constant or variable?
8. In general, is it better to limit the scope of a variable or to use the widest scope
possible?
9. What type of local variable persists data between procedure calls?
268 HOUR 11: Using Constants, Data Types, Variables, and Arrays
Answers
1. The Decimal data type
2. The Object data type
3. Visual Basic equates 0 to False and all nonzero values to True.
4. Constants are used to eliminate magic numbers.
5. Variables can have their values changed as often as necessary within their scope.
6. The first index is 0, and the last index is 5.
7. Scope describes the visibility of a constant, variable, or procedure.
8. It is better to use the narrowest scope possible.
9. Static variables persist their values between procedure calls.
Exercises
1. Create a project with a text box, button, and label control. When the user
clicks the button, move the contents of the text box to a variable, and then
move the contents of the variable to the label’s Text property. (Hint: A String
variable will do the trick.)
2. Rewrite the following code so that a single array variable is used rather than
two standard variables. (Hint: Do not use a multidimensional array.)
Dim strGameTitleOne As String
Dim strGameTitleTwo As String
strGameTitleOne = “Quake Wars: Enemy Territory”
strGameTitleTwo = “Orange Box”
269
HOUR 12
Performing Arithmetic,
String Manipulation, and
Date/Time Adjustments
What You’ll Learn in This Hour:
. Performing arithmetic
. Understanding the order of operator precedence
. Comparing equalities
. Understanding Boolean logic
. Manipulating strings
. Working with dates and times
Just as arithmetic is a necessary part of everyday life, it’s also vital to developing
Windows programs. You probably won’t write an application that doesn’t add, subtract,
multiply, or divide some numbers. In this hour, you’ll learn how to perform
arithmetic in code. You’ll also learn about order of operator precedence, which determines
how Visual Basic evaluates complicated expressions (equations). After you
understand operator precedence, you’ll learn how to compare equalities—something
that you’ll do all the time.
Boolean logic is the logic Visual Basic uses to evaluate expressions in decision-making
constructs. If you’ve never programmed before, Boolean logic might be a new concept
to you. In this hour, I explain what you need to know about Boolean logic to
create efficient code that performs as expected. Finally, I show you how to manipulate
strings and work with dates and times.
270 HOUR 12: Performing Arithmetic, String Manipulation, and Date/Time Adjustments
By the
Way
Performing Basic Arithmetic Operations
with Visual Basic
You have to have solid math skills to be a programmer; you’ll be performing a lot of
basic arithmetic when writing Visual Basic applications. To get the results you’re
looking for in any given calculation, you must
. Know the mathematical operator that performs the desired arithmetic function
. Understand and correctly use order of precedence
Using the correct mathematical operator is simple. Most are easy to commit to memory,
and you can always look up the ones you’re not quite sure of. I won’t go into
great detail on any of the math functions (if you’ve made it this far, I’m sure you
have a working grasp of basic math), but I will cover them all.
In Hour 15, “Debugging Your Code,” you’ll learn about the Debug.WriteLine()
method. You won’t be entering any code in this hour, but I use this method in
code snippets. All you need to know for these examples is that
Debug.WriteLine() sends a string to the Output window. For example,
Debug.WriteLine(“Dan Haught”) prints Dan Haught to the Output window.
Performing Addition
You perform simple addition by using the standard addition symbol, the + character.
The following line prints the sum of 4, 5, and 6:
Debug.WriteLine(4 + 5 + 6)
You don’t have to use a hard-coded value with arithmetic operators. You can use any
of the arithmetic operators on numeric variables and constants. For example:
Const c_FirstValue As Integer = 4
Const c_SecondValue As Integer = 5
Debug.WriteLine(c_FirstValue + c_SecondValue)
This bit of code prints the sum of the constants c_FirstValue and c_SecondValue,
which is 9.
Performing Subtraction and Negation
Like the addition operator, you’re probably familiar with the subtraction operator,
because it’s the same one you would use on a calculator or when writing an equation:
the – character. The following line of code prints 2 (the total of 6 – 4):
Debug.WriteLine(6 - 4)
Performing Basic Arithmetic Operations with Visual Basic 271
Did you
Know?
As with written math, the – character is also used to denote a negative number. For
example, to print the value –6, you would use a statement such as the following:
Debug.WriteLine(-6)
Performing Multiplication
If you work with adding machines, you already know the multiplication operator: the
* character. You can enter this character by pressing Shift+8 or by pressing the * key
located in the top row of the keypad section of the keyboard. Although you would
ordinarily use a × when writing multiplication equations such as 3 × 2 = 6 on paper,
you’ll receive an error if you try this in code; you have to use the * character. The following
statement prints 20 (5 multiplied by 4):
Debug.WriteLine(5 * 4)
Performing Division
You accomplish division by using the / operator. This operator is easy to remember if
you think of division as fractions. For example, one-eighth is written as 1/8, which literally
means 1 divided by 8. The following statement prints 8 (32 divided by 4):
Debug.WriteLine(32 / 4)
Be sure not to confuse the division character, /, with the backslash character, \. If
you use the backslash character, Visual Basic performs the division, but it returns
only the integer portion (the remainder is discarded).
Performing Exponentiation
Exponentiation is the process of raising a number to a certain power. An example is
102, which is 10 to the second power, or 100. The same equation in Visual Basic code
looks like this:
Debug.WriteLine(10 ^ 2)
The number placed to the left of the ^ operator is the base, whereas the number to
the right is the power/exponent. To get the ^ operator, press Shift+6.
Performing Modulus Arithmetic
Modulus arithmetic is the process of performing division on two numbers but keeping
only the remainder. You perform modulus arithmetic by using the Mod keyword,
rather than the / symbol. The following are examples of Mod statements and the values
they would print:
272 HOUR 12: Performing Arithmetic, String Manipulation, and Date/Time Adjustments
Debug.WriteLine(10 Mod 5) ‘ Prints 0
Debug.WriteLine(10 Mod 3) ‘ Prints 1
Debug.WriteLine(12 Mod 4.3) ‘ Prints 3.4
Debug.WriteLine(13.6 Mod 5) ‘ Prints 3.6
The first two statements are relatively easy to understand: 5 goes into 10 twice with
no remainder, and 3 goes into 10 three times with a remainder of 1. Visual Basic
processes the third statement as 4.3 going into 12 two times with a remainder of 3.4.
In the last statement, Visual Basic performs the Mod operation as 5 going into 13.6
twice with a remainder of 3.6.
Determining the Order of Operator Precedence
When several arithmetic operations occur within a single equation (called an
expression), Visual Basic has to resolve the expression in pieces. The order in which
these operations are evaluated is known as operator precedence. To fully understand
operator precedence, you have to brush up a bit on your algebra skills (most of the
math you perform in code will be algebraic).
Consider the following expression:
Debug.writeLine(6 + 4 * 5)
Two arithmetic operations occur in this single expression. To evaluate the expression,
Visual Basic has to perform both operations: multiplication and addition. Which
operation gets done first? Does it matter? Absolutely! If Visual Basic performs the
addition before the multiplication, you end up with the following:
Step 1: 6 + 4 = 10
Step 2: 10 * 5 = 50
The final result would be Visual Basic printing 50. Now look at the same equation
with the multiplication performed before addition:
Step 1: 4 * 5 = 20
Step 2: 20 + 6 = 26
In this case, Visual Basic would print 26—a dramatically different number from the
one computed when the addition gets performed first. To prevent these types of problems,
Visual Basic always performs arithmetic operations in the same order—the
order of operator precedence. Table 12.1 lists the order of operator precedence for
arithmetic and Boolean operators. (Boolean operators are discussed later in this
hour.) If you’re familiar with algebra, you’ll note that the order of precedence that
Visual Basic uses is the same as that used in algebraic formulas.
Performing Basic Arithmetic Operations with Visual Basic 273
TABLE 12.1 Visual Basic Order of Operator Precedence
Arithmetic Logical
Exponentiation (^) Not
Unary identity and negation (+, –)
Negation (–) And
Multiplication and division (*, /) Or
Integer division (\)
Modulus arithmetic (Mod)
Addition and subtraction (+, –)
String concatenation (&)
By the
Way
All comparison operators, such as >, <, and = (discussed in the next section), have
equal precedence. When operators have equal precedence, they are evaluated from
left to right. Notice that multiplication and division operators have equal precedence,
so an expression that has both these operators would be evaluated from left to right.
The same holds true for addition and subtraction. When expressions contain operators
from more than one category (arithmetic, comparison, or logical), arithmetic
operators are evaluated first, comparison operators are evaluated next, and logical
operators are evaluated last.
Just as when writing an equation on paper, you can use parentheses to override the
order of operator precedence. Operations placed within parentheses are always evaluated
first. Consider the previous example:
Debug.WriteLine(6 * 5 + 4)
Using the order of operator precedence, Visual Basic evaluates the equation like this:
Debug.WriteLine((6 * 5) + 4)
The multiplication is performed first, and then the addition. If you want the addition
performed before the multiplication, you could write the statement like this:
Debug.WriteLine(6 * (5 + 4))
When writing complex expressions, you have to be conscious of the order of operator
precedence and use parentheses to override the default precedence when
necessary. Personally, I try to always use parentheses so that I’m sure of what’s
happening and my code is easier to read.
274 HOUR 12: Performing Arithmetic, String Manipulation, and Date/Time Adjustments
Comparing Equalities
Comparing values, particularly variables, is even more common than performing
arithmetic (but you need to know how Visual Basic arithmetic works before you can
understand the evaluation of equalities).
Comparison operators are most often used in decision-making structures, as
explained in Hour 13, “Making Decisions in Visual Basic Code.” Indeed, the best way
to understand these operators is to use a simple If...Then decision structure. In an
If...Then construct, Visual Basic considers the expression on the If statement, and
if the expression equates to True, the code between the If and End If statements is
executed. For example, the following is an If...Then operation (a silly one at that)
expressed in English, not in Visual Basic code:
If dogs bark, then smile.
If this were in Visual Basic code format, Visual Basic would evaluate the If condition,
which in this case is “dogs bark.” If the condition is found to be True, the code following
Then is performed. Because dogs bark, you smile. Notice how these two things
(dogs barking and your smiling) are relatively unrelated. This doesn’t matter; the
point is that if the condition evaluates to True, certain actions (statements) occur.
You’ll often compare the value of one variable to that of another variable or to a specific
value when making decisions. The following are some basic comparisons and
how Visual Basic evaluates them:
Debug.WriteLine(6 > 3) ‘ Evaluates to True
Debug.WriteLine(3 = 4) ‘ Evaluates to False
Debug.WriteLine(3 >= 3) ‘ Evaluates to True
Debug.WriteLine(5 <= 4) ‘ Evaluates to False
Performing comparisons is pretty straightforward. If you get stuck writing a particular
comparison, attempt to write it in English before creating it in code.
Understanding Boolean Logic
Boolean logic is a special type of arithmetic/comparison. Boolean logic is used to
evaluate expressions to either True or False. This might be new to you, but don’t
worry—it isn’t difficult to understand. A logical operator is used to perform Boolean
logic. Consider the following sentence:
If black is a color and wood comes from trees, then print “ice cream.”
Understanding Boolean Logic 275
At first glance, this sentence might seem nonsensical. However, Visual Basic could
make sense of this statement by using Boolean logic. First, notice that three expressions
are actually being evaluated within this single sentence. I’ve added parentheses
in the following sentence to clarify the two most obvious expressions:
If (black is a color) and (wood comes from trees), then print “ice cream.”
Boolean logic evaluates every expression to either True or False. Therefore, substituting
True or False for each of these expressions yields the following:
If (True) and (True), then print “ice cream.”
Now, for the sake of clarity, here’s the same sentence with parentheses placed around
the final expression to be evaluated:
If (True And True), then print “ice cream.”
This is the point where the logical operators come into play. The And operator returns
True if the expressions on each side of the And operator are true (see Table 12.2 for a
complete list of logical operators). In the sentence we’re considering, the expressions
on both sides of the And operator are True, so the expression evaluates to True.
Replacing the expression with True yields the following:
If True, then print “ice cream.”
276 HOUR 12: Performing Arithmetic, String Manipulation, and Date/Time Adjustments
By the
Way
This would result in the words “ice cream” being printed. If the expression had evaluated
to False, nothing would print. As you’ll see in Hour 13, the decision constructs
always evaluate their expressions to either True or False, executing statements
according to the results.
As you work with Boolean logic, keep in mind that Visual Basic uses –1 to represent
True and 0 to represent False, as described in Hour 11, “Using Constants,
Data Types, Variables, and Arrays.” You should always use True or False in your
code, but just be aware of how Visual Basic treats the values internally.
Using the And Operator
The And operator is used to perform a logical conjunction. If the expressions on both
sides of the And operator evaluate to True, the And operation evaluates to True. If
either expression is False, the And operation evaluates to False, as illustrated in the
following examples:
Debug.WriteLine(True And True) ‘ Prints True
Debug.WriteLine(True And False) ‘ Prints False
Debug.WriteLine(False And True) ‘ Prints False
Debug.WriteLine(False And False) ‘ Prints False
Debug.WriteLine((32 > 4) And (6 = 6)) ‘ Prints True
Using the Not Operator
The Not operator performs a logical negation. That is, it returns the opposite of the
expression. Consider the following examples:
Debug.WriteLine(Not (True)) ‘ Prints False
Debug.WriteLine(Not (False)) ‘ Prints True
Debug.WriteLine(Not (5 = 5)) ‘ Prints False
Debug.WriteLine(Not(4 < 2)) ‘ Prints True
TABLE 12.2 Logical (Boolean) Operators
Operator Description
And Evaluates to True when the expressions on both sides are True.
Not Returns the opposite of the expression on which it operates.
It evaluates to True when the expression is False and False
when the expression is True.
Or Evaluates to True if an expression on either side evaluates
to True.
Xor Evaluates to True if one, and only one, expression on either side
evaluates to True.
Understanding Boolean Logic 277
The first two statements are easy enough; the opposite of True is False, and vice
versa. For the third statement, remember that Visual Basic’s operator precedence dictates
that arithmetic operators are evaluated first (even if no parentheses are used), so
the first step of the evaluation would look like this:
Debug.WriteLine(Not (True))
The opposite of True is False, so Visual Basic prints False.
The fourth statement would evaluate to
Debug.WriteLine(Not (False))
This happens because 4 is not less than 2, which is the expression Visual Basic evaluates
first. Because the opposite of False is True, this statement would print True.
Using the Or Operator
The Or operator is used to perform a logical disjunction. If the expression to the left or
right of the Or operator evaluates to True, the Or operation evaluates to True. The
following are examples that use Or operations, and their results:
Debug.WriteLine(True Or True) ‘ Prints True
Debug.WriteLine(True Or False) ‘ Prints True
Debug.WriteLine(False Or True) ‘ Prints True
Debug.WriteLine(False Or False) ‘ Prints False
Debug.WriteLine((32 < 4) Or (6 = 6)) ‘ Prints True
Using the Xor Operator
The Xor operator performs a nifty little function. I personally haven’t had to use it
much, but it’s great for those times when its functionality is required. If one—and only
one—of the expressions on either side of the Xor operator is True, the Xor operation
evaluates to True. Take a close look at the following statement examples to see how
this works:
Debug.WriteLine(True Xor True) ‘ Prints False
Debug.WriteLine(True Xor False) ‘ Prints True
Debug.WriteLine(False Xor True) ‘ Prints True
Debug.WriteLine(False Xor False) ‘ Prints False
Debug.WriteLine((32 < 4) Xor (6 = 6)) ‘ Prints True
278 HOUR 12: Performing Arithmetic, String Manipulation, and Date/Time Adjustments
Manipulating Strings
Recall from Hour 11 that a string is text. Visual Basic provides many functions for
working with strings. Although string manipulation isn’t technically arithmetic, the
things that you do with strings are similar to things you do with numbers, such as
adding two strings together; string manipulation is much like creating equations.
Chances are you’ll be working with strings a lot in your applications. Visual Basic
includes a number of functions that enable you to do things with strings, such as
retrieve a portion of a string or find one string within another. In the following sections,
you’ll learn the basics of string manipulation.
Concatenating Strings of Text
Visual Basic makes it possible to “add” two strings of text together to form one string.
Although purists will say it’s not truly a form of arithmetic, it’s much like performing
arithmetic on strings, so this hour is the logical place in which to present this material.
The process of adding two strings together is called concatenation. Concatenation
is very common. For example, you might want to concatenate variables with hardcoded
strings to display meaningful messages to the user, such as Are you sure you
wish to delete the user XXX?, where XXX is the contents of a variable.
To concatenate two strings, you use the & operator, as shown in this line of code:
Debug.WriteLine(“This is” & “a test.”)
This statement would print
This isa test.
Notice that there is no space between the words is and a. You could easily add a
space by including one after the word is in the first string or before the a in the second
string, or you could concatenate the space as a separate string, like this:
Debug.WriteLine(“This is” & “ “ & “a test.”)
Text placed directly within quotes is called a literal. Variables are concatenated in the
same way as literals and can even be concatenated with literals. The following code
creates two variables, sets the value of the first variable to “James,” and sets the value
of the second variable to the result of concatenating the variable with a space and
the literal “Foxall”:
Dim strFirstName as String
Dim strFullName as String
strFirstName = “James”
strFullName = strFirstName & “ “ & “Foxall”
Manipulating Strings 279
Did you
Know?
Did you
Know?
The final result is that the variable strFullName contains the string James Foxall.
Get comfortable concatenating strings of text—you’ll do this often!
In addition to the ampersand (&), Visual Basic lets you use the + sign to concatenate
strings—but don’t do this. It makes the code more difficult to read and might
yield incorrect results when you’re not using Option Strict.
Using the Basic String Functions
Visual Basic includes a number of functions that make working with strings of text
considerably easier than it might be otherwise. These functions enable you to easily
retrieve a piece of text from a string, compute the number of characters in a string,
and even determine whether one string contains another. The following sections summarize
the basic string functions.
Determining the Number of Characters Using Len()
The Len() function accepts a string (variable or literal) and returns the number of
characters in the string. The following statement prints 26, the total number of characters
in the literal string “Pink Floyd reigns supreme.” Remember, the quotes surrounding
the string tell Visual Basic that the text within them is a literal; they aren’t
part of the string. Len() is often used in support of the other string functions, as
you’ll learn next.
Debug.WriteLine(Len(“Pink Floyd reigns supreme.”)) ‘ Prints 26
Another way to get the number of characters in a string variable is to use the variable’s
Length method, as in
Debug.WriteLine(strMyStringVariable.Length())
Retrieving Text from the Left Side of a String Using
Microsoft.VisualBasic.Left()
The Microsoft.VisualBasic.Left() function returns a portion of the left side of the
string passed to it. The reason for the Microsoft.VisualBasic qualifier is that many
objects, including controls and forms, have Left properties. Using Left on its own is
ambiguous to the compiler, so it needs the full reference.
The Microsoft.VisualBasic.Left() function accepts two parameters:
. The string from which to retrieve a portion of the left side
. The number of characters to retrieve
280 HOUR 12: Performing Arithmetic, String Manipulation, and Date/Time Adjustments
The Microsoft.VisualBasic.Left() function always retrieves text starting with the
leftmost character. For example, the following statement prints Queen, the first five
characters of the string:
Debug.WriteLine(Microsoft.VisualBasic.Left(“Queen to Queen’s Level 3.”, 5))
Microsoft.VisualBasic.Left() is commonly used with the InStr() function (discussed
shortly) to retrieve the path portion of a variable containing a filename and
path combination, such as c:\Myfile.txt. If you know where the \ character is, you
can use Microsoft.VisualBasic.Left() to get the path.
If the number of characters requested is greater than the number of characters in
the string, the entire string is returned. If you’re unsure how many characters are
in the string, use the Len() function.
By the
Way
Retrieving Text from the Right Side of a String Using
Microsoft.VisualBasic.Right()
The Microsoft.VisualBasic.Right() function is the sister of the
Microsoft.VisualBasic.Left() function. Instead of returning text from the left
side of the string, Microsoft.VisualBasic.Right() returns text from the right side
of the string. Note, however, that the returned characters are always in the same
order in which they appear within the original string.
Microsoft.VisualBasic.Right() doesn’t retrieve the characters from right to left.
Instead, it starts at the rightmost character, counts back the number of characters you
specify, and returns that many characters from the right side of the string. The following
statement prints hing., the last five characters in the string:
Debug.WriteLine(Microsoft.VisualBasic.Right(“Duct tape fixes everything.”, 5))
Retrieving Text Within a String Using Mid()
When you need to retrieve a portion of text from within a string (from neither the left
side nor the right side), use the Mid() function. The Mid() function enables you to
specify where in the string to begin retrieving text, as well as how many characters to
retrieve. The Mid() function accepts the following three parameters:
. The string from which to retrieve a portion of text
. The character at which to begin retrieving text
. The number of characters to retrieve
Manipulating Strings 281
By the
Way
The following statement prints the text look li. This occurs because the Mid() function
begins at the fifth character (the l in look) and retrieves seven characters:
Debug.WriteLine(Microsoft.VisualBasic.Mid(“You look like you could “ _
& “use a monkey.”, 5, 7))
Not many people realize this, but you can omit the last parameter. When you do, the
Mid() function returns everything from the starting character to the end of the string.
The following statement prints the text ter crows at midnight.; it returns everything
beginning with the ninth character:
Debug.WriteLine(Mid(“The rooster crows at midnight.”, 9))
Determining Whether One String Contains Another Using
Instr()
At times you’ll need to determine whether one string exists within another. For example,
suppose that you let users enter their full name into a text box, and that you
want to separate the first and last names before saving them into individual fields in
a database. The easiest way to do this is to look for the space in the string that separates
the first name from the last. You could use a loop to examine each character in
the string until you find the space, but Visual Basic includes a native function that
does this for you, faster and easier than you could do it yourself: the InStr() function.
The basic InStr() function has the following syntax:
Instr([start, ] stringtosearch, stringbeingsought) ‘ Returns an Integer
The InStr() function has always been an enigma to me. For one thing, it’s the
only function I’ve ever seen in which the first parameter is optional, but the subsequent
parameters are required. Second, it’s documented with the second
parameter, called string1, and the third parameter, called string2. This makes
it difficult to remember which parameter is used for what and will probably force
you to reference the Help when you use this function.
The InStr() function searches one string for the occurrence of another. If the string is
found, the character location of the start of the matching search string is returned. If
the search string is not found within the other string, 0 is returned. The following
code searches a variable containing the text “James Foxall”, locates the space, and
uses Left() and Mid() to place the first and last names in separate variables:
Dim strFullName As String = “James Foxall”
Dim strFirstName As String
Dim strLastName As String
Dim intLocation As Integer
282 HOUR 12: Performing Arithmetic, String Manipulation, and Date/Time Adjustments
Function Description
Trim() Removes all leading and trailing spaces from the supplied string.
LTrim() Removes only the leading spaces from the supplied string.
RTrim() Removes only the trailing spaces from the supplied string.
intLocation = Instr(strFullName, “ “)
strFirstName = Microsoft.VisualBasic.Left(strFullName, intLocation - 1)
strLastName = Mid(strFullName, intLocation + 1)
This code assumes that a space will be found and that it won’t be the first or last
character in the string. Such code might need to be more robust in a real application,
such as checking to see whether InStr() returned 0, indicating that no
match was found.
Did you
Know?
When this code runs, InStr() returns 6, the location in which the first space is found.
Notice how I subtracted 1 from intLocation when using
Microsoft.VisualBasic.Left(). If I didn’t do this, the space would be part of the
text returned by Microsoft.VisualBasic.Left(). The same holds true with adding
1 to intLocation in the Microsoft.VisualBasic.Mid() statement.
I omitted the first parameter in this example because it’s not necessary when you
want to search from the first character in the string. To search from a different location,
supply the number of characters to begin searching from as the first parameter.
Trimming Beginning and Trailing Spaces from a String
In the previous example, I showed how you need to add 1 or subtract 1 from the
value returned by the InStr() function to avoid getting the space that was found as
part of your first or last names. As you work with strings, you’ll often encounter situations
in which spaces exist at the beginning or end of strings. Visual Basic includes
three functions for automatically removing spaces from the beginning or end of a
string (none of these functions removes spaces that exist between characters in a
string).
For example, consider that you didn’t subtract 1 from the value of intLocation in
the previous example. That is, you used a statement such as the following:
strFirstName = Microsoft.VisualBasic.Left(strFullName, intLocation)
strFirstName would contain the text “James “. Notice the space at the end of the
name. To remove the space, you could use Trim() or LTrim(), like this:
Working with Dates and Times 283
Did you
Know?
strFirstName = Trim(Microsoft.VisualBasic.Left(strFullName, intLocation))
Use Trim() in place of RTrim() or LTrim() unless you specifically want to keep
spaces at one end of the string.
Replacing Text Within a String
It’s not uncommon to have to replace a piece of text within a string with some other
text. Some people still put two spaces between sentences, for example, even though
this is no longer necessary because of proportional fonts. You could replace all double
spaces in a string with a single space by using a loop and the string manipulation
functions discussed so far, but there’s an easier way: the Replace() function. A basic
Replace() function call has the following syntax:
Replace(expression, findtext, replacetext)
The expression argument is the text to search, such as a string variable. The
findtext argument is used to specify the text to look for within expression. The
replacetext argument is used to specify the text used to replace the findtext. Consider
the following code:
Dim strText As String = “Give a man a fish”
strText = Replace(strText, “fish”, “sandwich”)
When this code finishes executing, strText contains the string “Give a man a sandwich”.
Replace() is a powerful function that can save many lines of code, and you
should use it in place of a homegrown replace function whenever possible.
Working with Dates and Times
Dates are a unique beast. In some ways, they act like strings, where you can concatenate
and parse pieces. In other ways, dates seem more like numbers in that you can
add to or subtract from them. You’ll often perform math-type functions on dates
(such as adding a number of days to a date or determining the number of months
between two dates), but you won’t use the typical arithmetic operations. Instead, you
use functions specifically designed for working with dates.
Understanding the Date Data Type
Working with dates is very common. You create a variable to hold a date by using the
Date data type. You can get a date into a Date variable in several ways. Recall that
when you set a string variable to a literal value, the literal is enclosed in quotes.
284 HOUR 12: Performing Arithmetic, String Manipulation, and Date/Time Adjustments
By the
Way
When you set a numeric variable to a literal number, the number is not enclosed in
quotes:
Dim strMyString As String = “This is a string literal”
Dim intMyInteger As Integer = 420
When setting a Date variable to a literal date, you enclose the literal in # signs, like this:
Dim dteMyBirthday As Date = #7/22/2010#
When using Option Strict, you cannot assign a string directly to a Date variable. For
example, if you let the user enter a date into a text box, and you want to move the
entry to a Date variable, you would have to do something like this:
dteMyDateVariable = CDate(txtBirthDay.Text)
You also have to convert a date to a string when moving it from a Date variable to a
text box (again, only when Option Strict is on). For more information on the data
type conversion functions, refer to Hour 11.
It’s important to note that Date variables store a date and a time—always. For example,
the following code:
Dim dteBirthday As Date = #7/22/2012#
Debug.WriteLine(dteBirthday)
produces this output:
7/22/2012 12:00:00 AM
Notice that the previous example outputs the time 12:00:00 AM, even though no
time was specified for the variable. This is the default time placed in a Date variable
when only a date is specified. Although a Date variable always holds a date and a
time, on occasion you’ll be concerned only with either the date or the time. Later, I’ll
show you how to use the Format() function to retrieve just the date or a time portion
of a Date variable.
Visual Basic includes a structure called DateTime. This structure has members
that enable you to do many things similar to the functions I discuss here. According
to Microsoft, neither method is preferred over the other. The DateTime structure
can be a bit more complicated, so I’ve chosen to cover the Date variable.
Working with Dates and Times 285
TABLE 12.3 Allowable Values for the interval Parameter of
DateAdd()
Enumeration Value String Unit of Time Interval to Add
DateInterval.Day d Day; truncated to integral value
DateInterval.DayOfYear y Day; truncated to integral value
DateInterval.Hour h Hour; rounded to nearest
millisecond
DateInterval.Minute n Minute; rounded to nearest
millisecond
DateInterval.Month m Month; truncated to integral
value
DateInterval.Quarter q Quarter; truncated to integral
value
DateInterval.Second s Second; rounded to nearest
millisecond
DateInterval.Weekday w Day; truncated to integral value
DateInterval.WeekOfYear ww Week; truncated to integral
value
DateInterval.Year yyyy Year; truncated to integral value
Adding To or Subtracting From a Date or Time
To add a specific amount of time (such as one day or three months) to a specific date
or time, use the DateAdd() function. It has the following syntax:
DateAdd(interval, number, date) As Date
Note that all three parameters are required. The first parameter is an enumeration (a
predefined list of values) and determines what you’re adding (month, day, hour,
minute, and so on). Table 12.3 lists the possible values for interval. The second
parameter is how much of the interval to add. The final parameter is a date. Supplying
a negative value for number subtracts that much of the interval from the date. For
example, to add 6 months to the date 7/22/69, you could use the following statements:
Dim dteMyBirthday As Date = #7/22/1969#
dteMyBirthday = DateAdd(DateInterval.Month, 6, dteMyBirthday)
After this second statement executes, dteMyBirthday contains the date 1/22/1970
12:00:00 AM.
286 HOUR 12: Performing Arithmetic, String Manipulation, and Date/Time Adjustments
By the
Way
You can use the literal string that corresponds to the enumeration (see Table
12.3), rather than using the enumerated name. For example, the previous statement
could be written as
dteMyBirthday = DateAdd(“m”, 6, dteMyBirthday)
By the
Way
The following code shows sample DateAdd() function calls and the date they would
return:
DateAdd(DateInterval.Year, 2, #3/3/1968#) ‘ Returns 3/3/1970 12:00:00 AM
DateAdd(DateInterval.Month, 5, #5/14/1998#) ‘ Returns 10/14/1998 12:00:00 AM
DateAdd(DateInterval.Month, -1, #3/6/2000#) ‘ Returns 2/6/2000 12:00:00 AM
DateAdd(DateInterval.Hour, -1, #6/28/1996 8:00:00 PM#) _
‘ Returns 6/28/1996 7:00:00 PM
Visual Basic never advances more calendar months than specified when adding
months. For example, DateAdd(“m”, 1, #1/31/2010#) produces the date
2/28/2010. Because February doesn’t have 31 days, Visual Basic uses the last
day of the month.
Determining the Interval Between Two Dates or
Times
The DateAdd() function enables you to easily add time to or subtract time from a
date or time. You can just as easily retrieve the interval between two existing dates or
times by using the DateDiff() function. The basic DateDiff() function has the following
syntax:
DateDiff(interval, Date1, Date2) As Long
The interval parameter accepts the same values as the interval parameter of the
DateAdd() function (refer to Table 12.3). The DateDiff() function returns a number
indicating the number of specified intervals between the two supplied dates. For
example, this code prints 9, the number of weeks between the two dates:
Dim dteStartDate As Date = #10/10/2010#
Dim dteEndDate As Date = #12/10/2010#
Debug.WriteLine(DateDiff(DateInterval.WeekOfYear, dteStartDate, dteEndDate))
Working with Dates and Times 287
If the second date comes before the first, the number returned is negative. The following
statements help illustrate how DateDiff() works by showing you some function
calls and the values they return:
DateDiff(DateInterval.Year, #7/22/1969#, #10/22/2001#) ‘ Returns 32
DateDiff(DateInterval.Month, #3/3/1992#, #3/3/1990#) ‘ Returns -24
DateDiff(DateInterval.Day, #3/3/1997#, #7/2/1997#) ‘ Returns 121
Notice that the second function call returns -24. Whenever the first date passed to
the DateDiff() function comes after the second date, a negative number is returned.
This is useful in determining the order of two dates. You can simply compare them
by using DateDiff() and determine which is the later date by seeing whether
DateDiff() returns a positive or negative number.
Retrieving Parts of a Date
Sometimes it can be useful to know just part of a date. For example, you might have
let a user enter his birth date, and you want to perform an action based on the
month in which he was born. To retrieve part of a date, use the DatePart() function.
The basic DatePart() function has the following syntax:
DatePart(interval, date) As Integer
Again, the possible values for interval are the same as those used for both
DateAdd() and DateDiff(). The following illustrates the use of DatePart():
DatePart(DateInterval.Month, #7/22/2010#) ‘ Returns 7
DatePart(DateInterval.Hour, #3:00:00 PM#) ‘ Returns 15 (military format)
DatePart(DateInterval.Quarter, #6/9/2010#) ‘ Returns 2
Formatting Dates and Times
As I stated earlier, at times you’ll want to work with only the date or time within a
Date variable. In addition, you’ll probably want to control the format in which a
date or time is displayed. All this is accomplished with the Format() function. The
Format() function can format all sorts of items in addition to dates and times, such
as monetary figures and strings. I can’t possibly tell you everything about the
Format() function here, but I do want to show you how to use Format() to output
either the date portion or the time portion of a Date variable.
The basic Format() function has the following syntax:
Format(expression, style)
The parameter expression is the expression to format, and style is a string specifying
the formatting. For example, to display the month portion of a date, you use M
288 HOUR 12: Performing Arithmetic, String Manipulation, and Date/Time Adjustments
in the style. Actually, specifying a single M displays the month as a single digit for 1
to 9 and as a double digit for 10 to 12. Specifying two Ms always shows the month in
double digits. Three Ms produce a three-digit abbreviated month, and four Ms return
the entire month name, regardless of how many characters are in the name. (Note:
lowercase m is used to return minutes, not months.) The following examples illustrate
this function:
Format(#1/22/2009#, “MM”) ‘ Returns 01
Format(#1/22/2009#, “MMM”) ‘ Returns Jan
Format(#1/22/2009#, “MMMM”) ‘ Returns January
There are formatting characters for years, days, hours, minutes, and even a.m. and
p.m. The list of allowable formatting characters is huge, and I encourage you to
explore them in the Visual Basic Help text. Because my goal here is to show you how
to extract a date or a time, I’ll show you some common formatting:
Format(#7/22/2009#, “MMM. d, yyyy”) ‘ Returns Jul. 22, 2009
Format(#7/22/2009#, “MMMM yyyy”) ‘ Returns July 2009
Format(#9:37:00 PM#, “h:mm tt”) ‘ Returns 9:37 pm
Format(#5/14/2009 9:37:00 PM#, “MM/dd/yyyy h:mm tt”) _
‘ Returns 05/14/2009 9:37 pm
As you can see, the comma, the colon, and the period characters are not symbolic but
appear in the formatted string in the location in which they are placed within style.
This information should be enough to get you going, but I highly encourage you to
explore the Format() function on your own—it’s a powerful and useful function.
Retrieving the Current System Date and Time
Visual Basic lets you retrieve the current system date and time. This is accomplished
by way of the DateTime structure. The DateTime structure has a number of members
that mimic the functionality of many of the date functions I’ve discussed, as well as
some additional members. One member, Today, returns the current system date. To
place the current system date in a new Date variable, for example, you could use a
statement such as this:
Dim dteToday As Date = DateTime.Today
To retrieve the current system date and time, use the Now property of DateTime, like this:
Dim dteToday As Date = DateTime.Now
Commit DateTime.Today and DateTime.Now to memory. You will need to retrieve
the system date and/or time at some point in the future, and this is by far the easiest
way to get that information.
Summary 289
Determining Whether a Value Is a Date
Often, I find it necessary to determine whether a value is a date. If I enable users to
enter their birthdays into a text box, for example, I want to ensure that they enter a
date before attempting to perform any date functions on the value. Visual Basic
includes a function just for this purpose: the IsDate() function. IsDate() accepts an
expression and returns True if the expression is a date and False if not.
The following statement prints True if the content of the text box is a date; otherwise,
it prints False:
Debug.WriteLine(IsDate(txtBirthday.Text))
Summary
Being able to work with all sorts of data is crucial to your success as a Visual Basic
developer. Just as you need to understand basic math to function in society, you need
to be able to perform basic math in code to write even the simplest of applications.
Knowing the arithmetic operators, as well as understanding the order of operator
precedence, will take you a long way in performing math with Visual Basic code.
Boolean logic is a special form of evaluation that Visual Basic uses to evaluate simple
and complex expressions down to a value of True or False. In the following
hours, you’ll learn how to create loops and how to perform decisions in code. What
you learned here about Boolean logic is critical to your success with loops and decision
structures; you’ll use Boolean logic perhaps even more often than you’ll perform
arithmetic.
Manipulating strings and dates involves special considerations. In this hour, you
learned how to work with both types of data to extract portions of values and to add
together pieces of data to form a new whole. String manipulation is straightforward,
and you’ll get the hang of it soon enough as you start to use some of the string functions.
Date manipulation, on the other hand, can be a bit tricky. Even experienced
developers need to refer to the online help at times. You learned the basics in this
hour, but don’t be afraid to experiment.
290 HOUR 12: Performing Arithmetic, String Manipulation, and Date/Time Adjustments
Q&A
Q. Should I always specify parentheses to ensure that operators are evaluated
as I expect them to be?
A. Visual Basic never fails to evaluate expressions according to the order of operator
precedence, so using parentheses isn’t necessary when the order of precedence
is correct for an expression. However, using parentheses assures you that
the expression is being evaluated the way you want it to be, and it might make
the expression easier for people to read. This really is your choice.
Q. I want to use the same custom date format whenever I work with dates. How
can I best accomplish this?
A. I’d create a global constant that represents the formatting you want to use,
and use that constant in your Format() calls as shown here. This way, if you
want to change your format, you have to change only the constant value, and
all Format() calls that use the constant will use the new value:
Const gc_MyUSDateFormat As String = “MMM. d, yyyy”
Debug.WriteLine(Format(dteStartDate, gc_MyUSDateFormat))
Be aware that if your application will be used in a country that uses a different
date format than you use, you should use the named date formats, such as
“General Date,” “Long Date,” or “Short Date.” Doing so ensures that the
proper date format for the user’s location will be used.
Workshop
Quiz
1. Which character is used to perform exponentiation?
2. To get only the remainder of a division operation, you use which operator?
3. Which operation is performed first in the following expression—the addition or
the multiplication?
x = 6 + 5 * 4
Workshop 291
4. Does the following expression evaluate to True or False?
((True Or True) And False) = Not True
5. Which Boolean operator performs a logical negation?
6. The process of appending one string to another is called what?
7. What function can be used to return the month of a given date?
8. What function returns the interval between two dates?
Answers
1. The ^ character
2. The Mod operator
3. 5 * 4 is performed first.
4. This expression equates to True.
5. The Not operator
6. Concatenation
7. The DatePart() function
8. The DateDiff() function
Exercises
1. Create a project that has a single text box on a form. Assume that the user
enters a first name, a middle initial, and a last name into the text box. Parse
the contents into three variables—one for each part of the name.
2. Create a project that has a single text box on a form. Assume that the user
enters a valid birthday into the text box. Use the date functions to tell the user
exactly how many days old he or she is.
This page intentionally left blank
Making Decisions Using If...Then 293
HOUR 13
Making Decisions in Visual
Basic Code
What You’ll Learn in This Hour:
. Making decisions using If...Then
. Expanding the capability of If...Then using Else and ElseIf
. Evaluating an expression for multiple values using Select Case
. Redirecting code flow using GoTo
In Hour 10, “Creating and Calling Code Procedures,” you learned to separate code
into multiple procedures so that they can be called in any order required. This goes a
long way in organizing code, but you still need a way to selectively execute code procedures
or groups of statements within a procedure. You use decision-making techniques
to accomplish this. Decision-making constructs are coding structures that
enable you to execute or omit code based on a condition, such as the value of a variable.
Visual Basic includes two constructs that enable you to make any type of
branching decision you can think of: If...Then...Else and Select Case.
In this hour, you’ll learn how to use the decision constructs provided by Visual Basic
to perform robust yet efficient decisions in Visual Basic code. In addition, you’ll learn
how to use the GoTo statement to redirect code within a procedure (and you’ll learn
when it’s not appropriate to use it). You’ll probably create decision constructs in every
application you build, so the quicker you master these skills, the easier it will be to
create robust applications.
Making Decisions Using If...Then
By far the most common decision-making construct used is the If...Then construct.
A simple If...Then construct looks like this:
If expression Then
... ‘ code to execute when expression is True.
End If
294 HOUR 13: Making Decisions in Visual Basic Code
The If...Then construct uses Boolean logic to evaluate an expression to either True
or False. The expression might be simple (If x=6 Then) or complicated (If x=6
And Y>10 Then). If the expression evaluates to True, the code placed between the If
statement and the End If statement gets executed. If the expression evaluates to
False, Visual Basic jumps to the End If statement and continues execution from
there, bypassing all the code between the If and End If statements.
You’ve already added at least one If...End construct to your Picture Viewer program.
For this example, you’ll create a separate sample project by following these steps:
1. Create a new Windows Application, and name it Decisions Example.
2. Right-click Form1.vb in the Solution Explorer, and choose Rename from the
shortcut menu. Change the name to DecisionsForm.vb, and set the form’s Text
property to Decisions Example.
3. Add a new text box to the form by double-clicking the TextBox icon in the toolbox.
Set the properties of the text box as follows:
Property Value
Name txtInput
Location 44, 44
4. Add a new button to the form by double-clicking the Button icon in the toolbox.
Set the button’s properties as follows:
Your form should now look like the one shown in Figure 13.1.
Now you’ll add code to the button’s Click event. This code uses a simple If...Then
construct and the Visual Basic function IsNumeric() to determine whether the text
Property Value
Name btnIsNumeric
Location 156, 42
Size 100, 23
Text Is text numeric?
Making Decisions Using If...Then 295
FIGURE 13.1
You’ll use
If...Then to
determine
whether text
entered in the
text box is a
number.
entered in the text box is numeric. Double-click the button now to access its Click
event, and enter the following code:
If IsNumeric(txtInput.Text) Then
MessageBox.Show(“The text is a number.”)
End If
This code is simple when examined one statement at a time. Look closely at the first
statement, and recall that a simple If...Then statement looks like this:
If expression Then
In the code you entered, expression is
IsNumeric(txtInput.Text)
IsNumeric() is a Visual Basic function that evaluates a given string and returns
True if the string is a number and False if it isn’t. Here, you’re passing the contents
of the text box to the IsNumeric() function and instructing Visual Basic to make a
decision based on the result. If IsNumeric()returns True, execution proceeds with
the line immediately following the If statement, and a message is displayed. If
IsNumeric() returns False, execution jumps to the End If statement, and no message
is displayed.
If you have only a single line of code to execute in a simple If...Then construct,
you can place the single statement of code immediately after the word Then and
omit the End If statement. For example, the code you entered could have been
entered like this:
If IsNumeric(txtInput.Text) Then MessageBox.Show(“The text is a number.”)
Although this code works, it’s considered a better practice to use an End If statement,
and I highly recommend that you do so because it makes the code much more
readable and less prone to errors.
296 HOUR 13: Making Decisions in Visual Basic Code
Executing Code When expression Is False
If you want to execute some code when expression evaluates to False, include an
Else statement between If and End If:
If expression Then
... ‘ code to execute when expression is True.
Else
... ‘ code to execute when expression is False.
End If
If you want to execute code only when expression equates to False, not when
True, use the Not operator in the expression, as in:
If Not(expression) Then
Refer to Hour 12, “Performing Arithmetic, String Manipulation, and Date/Time
Adjustments,” for more information on Boolean logic.
By the
Way
By including an Else clause, you can have one set of statements execute when
expression is True and another set of statements execute when expression is
False. In the example you just built, if users enter a number, they get a message.
However, if they don’t enter a number, they receive no feedback. Modify your code to
look like the following, which ensures that the user always gets a message:
If IsNumeric(txtInput.Text) Then
MessageBox.Show(“The text is a number.”)
Else
MessageBox.Show(“The text is not a number.”)
End If
If the user enters a number, the message The text is a number is displayed, but
nothing more. When Visual Basic encounters the Else statement, execution jumps to
the End If, because code within an Else statement executes only when expression
is False. Likewise, if the user enters text that isn’t a number, the message The text
is not a number is displayed, but nothing more; when expression evaluates to
False, execution immediately jumps to the Else statement.
Click Save All on the toolbar to save your work, and then press F5 to run the project.
Enter some text into the text box and click the button. A message box appears, telling
you whether the text you entered is numeric, as shown in Figure 13.2.
Feel free to enter other strings of text and click the button as often as you want. When
you’re satisfied that the code is working, choose Debug, Stop Debugging.
Get comfortable with If...Then. Odds are you’ll include at least one in every
project you create.
Did you
Know?
Making Decisions Using If...Then 297
FIGURE 13.2
If...Then
gives you great
flexibility in making
decisions.
Using ElseIf for Advanced Decision-Making
If...Then...Else gives you a lot of flexibility in making decisions. Visual Basic has
a statement that further expands the power of this construct and that can greatly
reduce the amount of code that might otherwise be needed to nest If...Then statements.
(Nesting involves placing one If...Then construct within another.) Specifically,
the ElseIf statement enables you to evaluate a second expression when an
If...Then statement equates to False.
The following shows a basic ElseIf structure:
If expression Then
...
ElseIf expression2 Then
...
End If
This code performs the same function as the following nested If...Then statements:
If expression Then
...
Else
If expression2 Then
...
End If
End If
The ElseIf statement not only reduces code, it also makes complex If...Then decision
structures much easier to read and follow. It’s important to note that you can use
multiple ElseIf statements and even use an Else as a catchall. For example:
If optSendToPrinter.Value Then
‘ Code to print document goes here.
ElseIf optSendToScreen.Value Then
‘ Code to perform a print preview goes here.
ElseIf optSendEmail.Value Then
‘ Code to email the document goes here.
298 HOUR 13: Making Decisions in Visual Basic Code
Else
‘ Code to execute if all above conditions are False.
End If
Be aware that the primary If statement and all its ElseIf statements are mutually
exclusive; only one will ever execute during any one execution of the construct.
By the
Way
Nesting If...Then Constructs
As mentioned earlier, you can nest If...Then statements to further refine your
decision-making process. The following code is an example of such a structure:
If optSendToPrinter.Value Then
If blnDriverSelected Then
‘ Print the document
Else
‘ Prompt for a printer driver.
End If
Else
...
End If
One thing to keep in mind when nesting If...Then constructs is that you must have
a corresponding End If statement for every If...Then statement. As mentioned earlier,
there is one exception to this rule, and that is when the If...Then statement
executes only one statement and that statement appears on the same line as
If...Then. Personally, I recommend against putting the code to execute on the same
line as the If statement, because it makes code more difficult to debug.
Evaluating an Expression for Multiple Values Using Select Case
At times, the If...Then construct can’t handle a decision situation without a lot of
unnecessary work. One such situation is when you need to perform different actions
based on numerous possible values of a single expression, not just True or False. For
example, suppose that you want to perform actions based on the user’s age. The following
shows what you might create using If...Then:
If lngAge < 10 Then
...
ElseIf lngAge < 18 Then
...
ElseIf lngAge < 21 Then
...
Else
...
End If
Making Decisions Using If...Then 299
As you can see, this structure is a bit difficult to follow. If you don’t analyze it from
top to bottom (as the compiler does), you might not even get the whole picture. For
example, if you looked at the last ElseIf, you might think that the code for that
ElseIf would execute if the user is younger than 21. However, when you realize that
the previous ElseIf statements catch all ages up to 18, it becomes apparent that the
last ElseIf runs only when the user is between 18 and 20. If you don’t see this, take a
moment to follow the logic until you do.
The important thing to realize in this example is that each ElseIf is really evaluating
the same expression (lngAge) but considering different values for the expression.
Visual Basic includes a much better decision construct for evaluating a single expression
for multiple possible values: Select Case.
A typical Select Case construct looks like this:
Select Case expression
Case value1
...
Case value2
...
Case value3
...
Case Else
...
End Select
Case Else is used to define code that executes only when expression doesn’t evaluate
to any of the values in the Case statements. Use of Case Else is optional.
Evaluating More Than One Possible Value in a
Case Statement
The Select Case statement enables you to create some difficult expression comparisons.
For example, you can specify multiple comparisons in a single Case statement
by separating the comparisons with a comma (,). Consider the following:
Select Case strColor
Case “Red”,”Purple”,”Orange”
‘ The color is a warm color.
Case “Blue”,”Green”,”Blue Violet”
‘ The color is a cool color.
End Select
When Visual Basic encounters a comma within a Case statement, it evaluates the
expression against each item in the comma-separated list. If expression matches
any one of the items, the code for the Case statement executes. This can reduce the
number of Case statements considerably in a complicated construct.
300 HOUR 13: Making Decisions in Visual Basic Code
Another advanced comparison is the keyword To. When To is used, Visual Basic looks
at the expression to determine whether the value is within a range designated by To.
Here’s an example:
Select Case lngAge
Case 1 To 7
‘ Code placed here executes if lngAge is 1, 7 or any number in between.
End Select
The keyword To can be used with strings as well. For example:
Select Case strName
Case “Hartman” To “White”
‘ Code placed here executes if the string is Hartman, White,
‘ or if the string falls alphabetically between these two names.
End Select
Here’s the age example shown earlier, but this time Select Case is used:
Select Case lngAge
Case < 10
...
Case 10 To 17
...
Case 18 To 20
...
Case Else
...
End Select
The Select Case makes this decision much easier to follow. Again, the key with
Select Case is that it’s used to evaluate a single expression for more than one possible
value.
Building a Select Case Example
Now you’ll build a project that uses advanced expression evaluation in a Select
Case structure. This simple application displays a list of animals to the user in a
combo box. When the user clicks a button, the application displays the number of
legs of the animal chosen in the list (if an animal is selected). Start by creating a new
Windows Application named Select Case Example, and then follow these steps:
1. Right-click Form1.vb in the Solution Explorer, choose Rename, and then change
the form’s name to SelectCaseExampleForm.vb. Next, set the form’s Text property
to Select Case Example (you have to click the form to view its design
properties).
2. Add a new combo box to the form by double-clicking the ComboBox item on
the toolbox. Set the combo box’s properties as follows:
Making Decisions Using If...Then 301
3. Add some items to the list. Click the Items property of the combo box, and
then click the Build button that appears in the property to access the String Collection
Editor for the combo box. Enter the text as shown in Figure 13.3; be sure
to press Enter at the end of each list item to make the next item appear on its
own line.
4. Add a Button control. When the button is clicked, a Select Case construct is
used to determine which animal the user selected and to tell the user how
many legs the selected animal has. Add a new button to the form by doubleclicking
the Button tool in the toolbox. Set the button’s properties as follows:
Property Value
Name btnShowLegs
Location 102, 130
Text Show Legs
Property Value
Name cboAnimals
Location 80, 100
FIGURE 13.3
Each line you
enter here
becomes an
item in the
combo box at
runtime.
Your form should now look like the one shown in Figure 13.4. Click Save All on the
toolbar to save your work before continuing.
All that’s left to do is add the code. Double-click the Button control to access its
Click event and then enter the following code:
302 HOUR 13: Making Decisions in Visual Basic Code
FIGURE 13.4
This example
uses only a
combo box and a
Button control.
Select Case cboAnimals.Text
Case “Bird”
MessageBox.Show(“This animal has 2 legs.”)
Case “Horse”, “Dog”, “Cat”
MessageBox.Show (“This animal has 4 legs.”)
Case “Snake”
MessageBox.Show (“This animal has no legs.”)
Case “Centipede”
MessageBox.Show (“This animal has 100 legs.”)
Case Else
MessageBox.Show (“You did not select from the list!”)
End Select
Here’s what’s happening:
. The Select Case construct compares the content of the cboAnimals combo
box to a set of predetermined values. Each Case statement is evaluated in the
order in which it appears in the list. Therefore, the expression is first compared
to “Bird.” If the content of the combo box is Bird, the MessageBox.Show()
statement immediately following the Case statement is called, and code execution
then jumps to the End Select statement.
. If the combo box doesn’t contain Bird, Visual Basic looks to see whether the
content is “Horse,” “Dog,” or “Cat.” If the combo box contains any of these values,
the MessageBox.Show() statement following the Case statement is called,
and execution then jumps to the End Select statement.
. Each successive Case statement is evaluated the same way. If no matches are
found for any of the Case statements, the MessageBox.Show() in the Case
Else statement is called. If there are no matches and no Case Else statement,
no code executes.
Select Case uses case-sensitive comparisons. If the user enters horse, Select
Case does not consider it the same as Horse.
By the
Way
Making Decisions Using If...Then 303
As you can see, the capability to place multiple possible values for the expression in a
single Case statement reduces the number of Case statements as well as redundant
code (code that would have to be duplicated for each Case statement in which animals
had the same number of legs). Also, adding a new animal to the list can be as
simple as adding the animal’s name to an existing Case statement.
Try it now by pressing F5 to run your project, and then follow these steps:
1. Select an animal from the list and click the button.
2. Try clearing the contents of the combo box and click the button.
3. When you’re finished, choose Debug, Stop Debugging to stop the project, and
click Save All on the toolbar.
Creative Uses of Select Case
You might be surprised at what you can do with a Select Case statement. One of
the coolest tricks I know uses Select Case to determine which radio button in a
group is selected.
When a radio button is selected, its Checked property returns True. Essentially, this
means that you have to look at the Checked property of each radio button in a group
until you find the one that’s set to True. The Visual Basic documentation recommends
using an If...Then construct like this:
Dim strMessage As String = “You selected “
If radioButton1.Checked = True Then
strMessage = strMessage & radioButton1.Text
ElseIf radiobutton2.Checked = True Then
strMessage = strMessage & radioButton2.Text
ElseIf radiobutton3.Checked = True Then
strMessage = strMessage & radioButton3.Text
End If
MessageBox.Show(strMessage)
In my opinion, all those ElseIf statements are messy. Consider this: Although you’re
looking at the Checked property of a number of radio button controls, you’re comparing
them all to a single value: the value True.
Now, if you look at True as the expression and the Checked properties of the controls
as the possible values, you can replace the If...Then construct with a Select Case
construct such as the following:
Dim strMessage As String = “You selected “
Select Case True
Case radioButton1.Checked
strMessage = strMessage & radioButton1.Text
Case radioButton2.Checked
304 HOUR 13: Making Decisions in Visual Basic Code
strMessage = strMessage & radioButton2.Text
Case radioButton3.Checked
strMessage = strMessage & radioButton3.Text
End Select
MessageBox.Show(strMessage)
This seems much tidier to me. You can pretty much accomplish any decision-making
task you can think of using If...Then, Select Case, or a combination of both. The
skill comes in creating the cleanest and most readable decision structure possible.
You can nest Select Case constructs within one another. In addition, you can
nest Select Case constructs within If...Then constructs and vice versa. You
can pretty much nest decision constructs in any way you see fit.
By the
Way
Branching Within a Procedure Using GoTo
Decision structures are used to selectively execute code. When a decision statement is
encountered, Visual Basic evaluates an expression and diverts code according to the
result. However, you don’t have to use a decision structure to divert code because
Visual Basic includes a statement that can be used to jump code execution to a predetermined
location within the current procedure: the GoTo statement.
Before I talk about how to use GoTo, I want to say that under most circumstances, it’s
considered bad coding practice to use a GoTo. Code that’s heavily laden with GoTo
statements is difficult to read and debug because the execution path is so convoluted.
Such code is often called spaghetti code, and it should be avoided at all costs. I’d say
that in 99% of the situations in which GoTo is used, there’s a better approach to the
problem. I’ll show an example of just such a case shortly. Nevertheless, GoTo, like all
other statements, is a tool. Although it’s not needed as often as some of the other
Visual Basic statements, it’s still a useful tool to have at your disposal—when used
judiciously.
To jump to a specific location in a procedure, you must first define the jump location
by using a code label. A code label is not the same as a label control that you place on
a form. You create a code label by positioning the cursor on a new line in a procedure,
typing in a name for the label followed by a colon, and pressing Enter. Code
labels can’t contain spaces, and they can’t be a Visual Basic reserved word. You can’t
create a code label called Print because Print is a reserved word in Visual Basic, for
example. However, you could create a label called PrintAll, because PrintAll isn’t a
reserved word. Code labels act as pointers that you can jump to when you use GoTo.
The following shows an example using GoTo to jump code execution to a label:
Private Sub GotoExample()
Dim intCounter As Integer = 0
Branching Within a Procedure Using GoTo 305
IncrementCounter:
intCounter = intCounter + 1
If intCounter < 5000 Then GoTo IncrementCounter
End Sub
This procedure does the following:
. Dimensions an Integer variable called intCounter and initializes it with a
value of 0.
. Defines a code label titled IncrementCounter. One or more GoTo statements
can be used to jump code execution to this label at any time.
. Increments intCounter by 1.
. Uses an If...Then statement to determine whether intCounter has exceeded
5000. If it hasn’t, a GoTo statement forces code execution back to the
IncrementCounter label, where intCounter is incremented and tested again,
creating a loop.
This code works, and you’re welcome to try it. However, this is terrible code. Remember
how I said that the use of a GoTo can often be replaced by a better coding
approach? In this case, Visual Basic has specific looping constructs that you’ll learn
about in Hour 14, “Looping for Efficiency.” These looping constructs are far superior
to building your own loop under most conditions, so you should avoid building a
loop that uses a GoTo statement. As a matter of fact, one of the biggest misuses of
GoTo is using it in place of one of Visual Basic’s internal looping constructs. In case
you’re interested, here’s the loop that would replace the use of GoTo in this example:
Dim intCounter As Integer
For intCounter = 1 To 5000
...
Next intCounter
This discussion might leave you wondering why you would ever use GoTo. One situation
in which I commonly use GoTo statements is to create single exit points in a procedure.
As you know, you can use Exit Sub or Exit Function to force execution to
leave a procedure at any time. Cleanup code is often required before a procedure
exits. In a long procedure, you might have many exit statements. However, such a
procedure can be difficult to debug because cleanup code might not be run under all
circumstances. All procedures have a single entry point, and it makes sense to give
them all a single exit point. With a single exit point, you use a GoTo statement to go
to the exit point, rather than an Exit statement. The following procedure illustrates
using GoTo to create a single exit point:
Private Sub DoSomething()
If expression = True Then
‘ some code here that makes it necessary to exit.
306 HOUR 13: Making Decisions in Visual Basic Code
GoTo PROC_EXIT
Else
‘ some more code here
End If
‘ some more code here
PROC_EXIT:
‘ Put any clean up code here
Exit Sub
End Sub
An even better approach to creating a single exit point is to wrap the contents
of a procedure in a Try...Catch...Finally block, as discussed in Hour 15,
“Debugging Your Code.” If you’re interested in using industry-accepted best practices
to create the soundest code possible, I suggest that you take a look at
my book Practical Standards for Microsoft Visual Basic .NET, Second Edition
(Microsoft Press, 2002).
By the
Way
Summary
In this hour you learned how to use Visual Basic’s decision constructs to make decisions
in Visual Basic code. You learned how to use If...Then statements to execute
code when an expression evaluates to True and to use Else to run code when the
expression evaluates to False. For more complicated decisions, you learned how to
use ElseIf statements to add further comparisons to the decision construct. You even
learned how you can nest If...Then structures for more flexibility.
In addition to If...Then, you learned how to use Select Case to create powerful
decision constructs that evaluate a single expression for many possible values. You
learned how you can check for multiple possible values with a single Case statement,
which can greatly increase legibility and reduce redundancy. Finally, you learned
that mixing creativity with Select Case can yield some useful results.
Decision-making constructs are often the backbone of applications. Without the
capability to run specific sets of code based on changing situations, your code would
be very linear and, as a result, very limited. Become comfortable with the decision
constructs, and make a conscious effort to use the best construct for any given situation.
The better you are at writing decision constructs, the faster you’ll be able to produce
solid and understandable code.
Workshop 307
Q&A
Q. What if I want to execute code only when an expression in an If...Then
statement is False, not True? Do I need to place the code in an Else clause
with no code after the Then?
A. This is where Boolean logic helps. You need to make the expression evaluate to
True for the code you want to run. You do this by using the Not operator, like this:
If Not expression Then
Q. How important is the order in which Case statements are created?
A. It depends on the situation. In the earlier example in which the selected animal
was considered and its number of legs was displayed, the order has no
effect. If you’ll perform numeric comparisons, such as the age example shown
in this hour, the order is critical. If you’re not careful, you can prevent a Case
statement from ever being evaluated. For example, comparing a variable to
<12 before comparing it to =6 would mean that the first comparison would
evaluate to True if the variable were 6, so the second comparison would never
take place.
Workshop
Quiz
1. Which decision construct should you use to evaluate a single expression to
either True or False?
2. Evaluating expressions to True or False for both types of decision constructs is
accomplished using what kind of logic?
3. If you want code to execute when the expression of an If...Then statement
evaluates to False, you should include what kind of clause?
4. True or false: You don’t need an End If statement when only one statement is
to execute when an expression in an If...Then statement evaluates to True.
5. Which decision construct should you use when evaluating the result of an
expression that might equate to one of many possible values?
6. To place multiple possible values on a single Case statement, you separate
them with what?
308 HOUR 13: Making Decisions in Visual Basic Code
7. Is it possible that more than one Case statement in a single Case construct
might have its code execute?
8. True or false: You can use GoTo to jump code execution to a different procedure.
9. To use GoTo to jump execution to a new location in code, what must you create
as a pointer to jump to?
Answers
1. The If...Then construct
2. Boolean
3. Else
4. True, but the code is less readable and more difficult to debug.
5. Select Case
6. A comma (,)
7. No, never.
8. False. GoTo can move code execution only within the current procedure.
9. A code label
Exercises
1. Create a project that enables the user to enter text into a text box. Use an
If...Then construct to determine whether the text entered is a circle, triangle,
square, or pentagon, and display the number of sides the entered shape has. If
the text doesn’t match one of these shapes, let the users know that they must
enter a valid shape.
2. Rewrite the following code using only an If...Then structure; the new code
should not contain a GoTo:
...
If Not(blnAddToAge) Then GoTo SkipAddToAge
intAge = intAge + 1
SkipAddToAge:
Looping a Specific Number of Times Using For...Next 309
HOUR 14
Looping for Efficiency
What You’ll Learn in This Hour:
. Looping a specific number of times using For...Next
. Looping based on a condition using Do...Loop
You will often encounter situations in which you need to execute the same code statement
or group of statements repeatedly. You will need to execute some of these statements
a specific number of times, whereas others might need to be executed as long
as a certain condition persists (an expression is True) or until a condition occurs (an
expression becomes True). Visual Basic includes constructs that enable you to easily
define and execute these repetitive code routines: loops. This hour shows you how to
use the two major looping constructs to make your code smaller, faster, and more
efficient.
Looping a Specific Number of Times
Using For...Next
The simplest type of loop you can create is the For...Next loop, which has been
around since the earliest forms of the BASIC language. With a For...Next loop, you
instruct Visual Basic to begin a loop by starting a counter at a specific value. Visual
Basic then executes the code within the loop, increments the counter by a defined
incremental value, and repeats the loop until the counter reaches an upper limit
you’ve set. The following is the general syntax for the basic For...Next loop:
For countervariable = start To end [Step step]
... [statements to execute in loop]
[Exit For]
... [statements to execute in loop]
Next [countervariable]
310 HOUR 14: Looping for Efficiency
TABLE 14.1 Components of the For Statement
Part Description
countervariable A previously declared variable of a numeric data type
(Integer, Long, and so on). This variable is incremented
each time the loop occurs.
start The number from which you want to start counting.
end The number to which you want to count. When
countervariable reaches the end number, the statements
within the For...Next loop are executed a final time, and
execution continues with the line following the Next
statement.
step The amount by which you want countervariable
incremented each time the loop is performed. step is an
optional parameter; if you omit it, countervariable is
incremented by 1.
Exit For A statement that can be used to exit the loop at any time.
When Exit For is encountered, execution jumps to the
statement following Next.
Initiating the Loop Using For
The For statement both sets up and starts the loop. The For statement has the components
described in Table 14.1.
Closing the Loop with the Next Statement
Every For statement must have a corresponding Next statement. You don’t have to
specify the countervariable name with the Next statement, but you should because
it makes the code easier to read. The following are examples of simple For...Next
loops, along with explanations of what they do.
Dim intCounter As Integer
For intCounter = 1 To 100
debug.WriteLine(intCounter)
Next intCounter
This routine declares an Integer variable named intCounter and then starts a loop
with a For statement. The loop initializes intCounter at 1, prints the value of
intCounter, increments intCounter by 1, and continues looping. Because step has
been omitted, the variable intCounter is increased by 1 every time the loop is performed.
This loop would execute 100 times, printing the numbers 1 through 100 to
the Immediate window.
Looping a Specific Number of Times Using For...Next 311
This next routine performs the same as the preceding example:
Dim intCounter As Integer
For intCounter = 1 To 100
debug.WriteLine(intCounter)
Next
Note that the Next statement doesn’t specify the name of the counter whose loop is
to be executed. This is perfectly legal, but it’s not good coding practice. Consider the
following example:
Dim intCounter As Integer
Dim intSecondCounter as Integer
For intCounter = 1 To 100
For intSecondCounter = 1 to 100
debug.WriteLine(intSecondCounter)
Next intSecondCounter
Next intCounter
This code executes a loop within a loop. If you omitted the variable names on the
Next statements, the code would run, but from a programmer’s standpoint, it would
be difficult to read and understand.
Specifying an Increment Value Using Step
Step is used in a For...Next statement to designate the value by which to increment
the counter variable each time the loop occurs. As you’ve seen, when Step is
omitted, the counter variable is incremented by 1—always. If you want the counter
variable incremented by 1, you don’t need to use Step (it doesn’t make the code any
easier to read). However, if you need to increment the counter variable by a value
other than 1, you must use Step.
Here’s an example of a simple For...Next loop that uses Step:
Dim intCounter As Integer
For intCounter = 1 To 100 Step 4
debug.WriteLine(intCounter)
Next intCounter
This code works much like that in the first example, except that each time Next is
reached, intCounter is incremented by 4 rather than by 1. This loop would execute
a total of 25 times (not 100 times). To create a For...Next loop that counts backward,
specify a negative value for Step, as shown here:
Dim intCounter As Integer
For intCounter = 100 To 1 Step -1
debug.WriteLine(intCounter)
Next intCounter
312 HOUR 14: Looping for Efficiency
This loop initializes intCounter at a value of 100 and decrements intCounter by 1
each time Next is reached. The loop executes until intCounter is reduced to 1 (the
End value). Be aware that you don’t have to use whole numbers for step; you could
use a number such as 0.5. If you do, the data type of the counter variable needs to
support fractions, so you can’t use Integer.
Exiting a Loop Early
Although you’ll know the start and end of a For...Next loop when you initialize it
(you have to specify a start and end, or you can’t create the loop), at times you’ll
need to exit a loop before you reach the end value. To exit a For...Next loop at any
time, use the Exit For statement, as shown in the following example:
Dim intCounter As Integer
For intCounter = 1 To 100
If condition Then Exit For
debug.WriteLine(intCounter)
Next intCounter
When Visual Basic encounters an Exit For statement, code execution jumps immediately
to the statement following the Next statement of the current loop construct—
the loop stops. In this example, condition could be a variable or any expression.
condition is usually something that changes during the lifetime of the loop; if
condition doesn’t change, there’s no point in evaluating it. For example, you might
loop through a list of files, trying to find a specific file. After you find it, there’s no
need to continue looking, so you exit the loop.
Continuing Looping Before Next Is Reached
Relatively new to Visual Basic is the capability to continue a For...Next loop before
encountering the Next statement. To do this, you use the statement Continue For,
as shown here:
For countervariable = 1 to 1000
If expression Then
Continue For ‘ Acts just like the Next statement
End If
‘ Other code...
Next countervariable
Creating a For...Next Example
Now you’ll create a procedure containing a For...Next loop that counts from 100 to
0 and sets the opacity of a form to the value of the counter (the form will fade out).
Looping a Specific Number of Times Using For...Next 313
Property Value
Name btnFadeForm
Location 105, 113
Size 75, 23
Text Fade Form
Create a new Windows Application named Fading Form, and then follow these steps:
1. Right-click Form1.vb in the Solution Explorer, choose Rename, and change the
name of the default form to FadingFormForm.vb. Next, set the form’s Text property
to Fading Form (you’ll need to click the form to access its design properties).
2. Add a button to the form by double-clicking the Button item in the toolbox. Set
the button’s properties as follows:
Your form should look like the one shown in Figure 14.1.
All that’s left to do is to write the code. Double-click the button to access its Click
event, and enter the following:
Dim sngOpacity As Single
For sngOpacity = 1 To 0 Step -0.05
Me.Opacity = sngOpacity
‘ Let the form repaint itself.
Me.Refresh()
‘ Create a delay.
System.Threading.Thread.Sleep(200)
Next
‘ Show the form again.
Me.Opacity = 1
FIGURE 14.1
This simple project
does something
pretty
cool...
314 HOUR 14: Looping for Efficiency
Much of this code should make sense to you by now. Here’s what’s happening:
. The first statement creates a variable of type Single. We’re using Single
because Opacity works with values of 0 to 1. Integers don’t support decimal
places. In fact, I wasn’t paying attention when I first wrote this code, used an
integer, and the code didn’t work. Try it and see! It took me a minute or two to
figure out what was happening. If you look at a situation like this and think of
it as a puzzle, you’ll really enjoy programming!
. The next statement starts the For...Next loop. The variable is initialized to 1,
and Step indicates that the variable will have its value decremented by .05
each time the loop starts a new iteration.
. The third line sets the form’s Opacity to the value of the variable. The next
line (after the comment) calls the form’s Refresh() method, which forces it to
repaint itself. If you don’t do this, Windows might not get around to repainting
the form between iterations. Comment out the Refresh() statement to see
what happens. (In other words, put a comment character in front of the statement
so that Visual Basic treats it as a comment and doesn’t execute it.)
. The next statement (the Sleep() statement) tells Visual Basic to pause. The
number in parentheses is the number of milliseconds to wait—in this case, 200.
This is a nifty function! We could have used another For...Next loop to create
a pause, but then the duration of the pause would depend on the speed of the
user’s computer. By using Sleep(), we’ve guaranteed that the pause will be the
same on every machine that executes this code.
. The Next statement sends execution back to the For statement, where the
variable is decremented and tested to make sure that we haven’t reached the
stop value.
. When the loop is finished, the form will be invisible. The last statement simply
sets Opacity back to 1, showing the form.
Click Save All on the toolbar and press F5 to run the project. When the form first
appears, it looks normal. Click the button, though, and watch the form fade out (see
Figure 14.2)!
If you were to forgo a loop and write each line of code necessary to change the opacity,
you would have to duplicate the statements 20 times each! Using a simple
For...Next loop, you performed the same task in just a few lines of code.
Use a For...Next loop when you know how many times you want the loop to execute.
This doesn’t mean that you have to know how many times you want the loop to
Using Do...Loop to Loop an Indeterminate Number of Times 315
FIGURE 14.2
This would take
a lot of code
without a loop!
execute at design time. It simply means that you must know how many times you
want the loop to execute when you first start the loop. You can use a variable to define
any of the parameters for the For...Next loop, as illustrated in the following code:
Dim intCounter As Integer
Dim intUpperLimit as Integer
intUpperLimit = 100
For intCounter = 1 To intUpperLimit
debug.WriteLine(intCounter)
Next intCounter
One of the keys to writing efficient code is to eliminate redundancy. If you find
yourself typing the same (or a similar) line of code repeatedly, chances are it’s a
good candidate for a loop.
Did you
Know?
Using Do...Loop to Loop an
Indeterminate Number of Times
In some situations, you won’t know the exact number of times a loop must be performed—
not even when the loop begins. You could start a For...Next loop specifying
an upper limit that you know is larger than the number of loops needed, check
for a terminating condition within the loop, and exit the loop using an Exit For
316 HOUR 14: Looping for Efficiency
statement when the condition is met. However, this approach is inefficient and usually
impractical. When you need to create such a loop, using Do...Loop is the
answer.
Creating a Do...Loop
Do...Loop comes in a number of flavors. Its most basic form has the following syntax:
Do
[Statements]
Loop
Ending a Do...Loop
A Do...Loop without some sort of exit mechanism or defined condition is an endless
loop. In its most basic form (shown previously), nothing is present to tell the loop
when to stop looping. At times you might need an endless loop (game programming
is an example), but most often you’ll need to exit the loop when a certain condition is
met. Like the For...Next loop, the Do...Loop has a statement you can use to exit
the loop at any time: the Exit Do statement. For example, you could expand the
Do...Loop we’re discussing to include an Exit Do statement such as the following:
Do
[Statements]
If expression Then Exit Do
Loop
In this code, the loop would execute until expression evaluates to True. Generally,
the expression is based on a variable that’s modified somewhere within the loop.
Obviously, if the expression never changes, the loop never ends.
You can build an expression into the Do...Loop structure itself by using one of two keywords:
While or Until. The following is a simple Do...Loop using the While keyword:
Do While expression
[Statements]
Loop
As long as expression evaluates to True, this loop continues to occur. If expression
evaluates to False when the loop first starts, the code between the Do While and
Loop statements doesn’t execute—not even once.
Here’s a similar Do...Loop that uses the Until keyword:
Do Until expression
[Statements]
Loop
Using Do...Loop to Loop an Indeterminate Number of Times 317
This loop behaves differently from the loop that uses While. When you define a loop
using the keyword Until, the loop executes repeatedly until expression evaluates to
True. As long as expression is False, the loop occurs. This is essentially the opposite
behavior of While. If expression is True when the loop begins, the code between the
Do Until and Loop statements doesn’t execute—not even once.
Notice how both While and Until can prevent the loop from executing. This occurs
because expression is placed on the Do statement, which means that it’s evaluated
before the loop is entered and again each time the loop iterates. You can put a While
or Until on the Loop statement rather than on the Do statement, which means that
the loop executes once before expression is evaluated for the first time. Such loops
always occur at least once. You need to be aware of how this changes the loop’s
behavior. Here’s the previous example with the While keyword placed on the Loop
statement:
Do
[Statements]
Loop While expression
Again, this loop executes as long as expression evaluates to True. The difference
between the Do...While and Do...Loop While loops is that code between the Do
and the Loop While statements always executes at least once; expression isn’t evaluated
until the loop has completed its first cycle. Again, such a loop always executes
at least once, regardless of the value of expression. Here’s the same code shown previously,
this time with the Until keyword placed on the Loop statement rather than
on the Do statement:
Do
[Statements]
Loop Until expression
This loop executes until expression evaluates to True. However, the code within this
loop always executes at least once; expression isn’t evaluated until the loop completes
its first cycle.
You can use Continue Do within a Do...Loop to send execution back to the Do
statement, just as though the Loop statement were reached.
By the
Way
Creating a Do...Loop Example
Now you’ll create an example using a Do...Loop. In this project, you’ll find the first
10 numbers that are evenly divisible by 3. Although you know you want to find 10
numbers, you don’t know how many numbers you will have to evaluate. Therefore,
the Do...Loop is the best choice.
318 HOUR 14: Looping for Efficiency
Property Value
Name lstResults
Location 82, 68
Size 120, 160
Property Value
Name btnFindNumbers
Location 82, 39
Size 120, 23
Text Find Numbers
FIGURE 14.3
What better control
to show a
list of results
than a list box?
Create a newWindows Application named No Remainders, and then follow these steps:
1. Rename the form NoRemaindersForm.vb, and set its Text property to No
Remainders.
2. Add a button to the form, and set its properties as follows:
3. Add a ListBox control to the form, and set its properties as follows:
Your form should look like the one shown in Figure 14.3.
Double-click the new button to access its Click event, and then enter the following
code:
Dim intSeek As Integer = 1
Dim intFound As Integer = 0
Do Until intFound = 10
If intSeek Mod 3 = 0 Then
lstResults.Items.Add(CStr(intSeek))
intFound = intFound + 1
Using Do...Loop to Loop an Indeterminate Number of Times 319
End If
intSeek = intSeek + 1
Loop
Again, this code is more easily understood when broken down:
. The first two statements simply create a couple of integer variables. The variable
intSeek will be the number you’ll test to see whether it’s evenly divisible
by 3 (meaning that it has no remainder). The variable intFound will be the
counter; you’ll increment this by 1 each time you find a number that is evenly
divisible by 3.
. The Do statement starts the loop. The condition ensures that the loop will continue
to function until 10 numbers are found (intFound = 10).
. In Hour 12, “Performing Arithmetic, String Manipulation, and Date/Time
Adjustments,” I mentioned how the Mod operator can be used to determine a
remainder. Here Mod is being used to determine whether intSeek is divisible by
3; it determines whether there is a remainder when intSeek is divided by 3.
. If the results of the regular division and the integer division are the same, there
is no remainder. You then add the number to the results list box and increment
intFound by 1.
. The next step is to increase intSeek so that you can test the next number.
. The last statement is Loop. This sends execution back to the Do statement. If
intFound = 10, the loop doesn’t execute; instead, the execution path is sent to
the line following the Loop statement. If intFound is less than 10, the loop executes
once more.
Click Save All on the toolbar to save the project, and then press F5 to run it. Click the
Find Numbers button, and watch the results fill up—fast (see Figure 14.4)!
FIGURE 14.4
Visual Basic performs
math functions
very
quickly.
320 HOUR 14: Looping for Efficiency
By the
Way
The Do...Loop was the best choice here because you didn’t know how many numbers
you needed to evaluate (that is, how many times to iterate the loop). If you
wanted to search only the numbers from 1 to 100, for example, a For...Next loop
would be better.
Visual Basic supports one more loop type: the While...End While loop. This
loop is almost the same as the Do...Loop. (While...End While does the same
thing as the Do...Loop but uses different syntax.) However, the Do...Loop is
more widely accepted (While...End While is a holdover from earlier versions of
Visual Basic). I highly recommend that you not use the While...End While loop;
instead, use the Do...Loop.
Summary
Looping is a powerful technique that enables you to write tighter code. Tighter code
is smaller, more efficient, and usually—but not always—more readable. In this hour,
you learned to write For...Next loops for situations in which you know the precise
number of times you want a loop to execute. Remember, it’s not necessary to know
the number of iterations at design time, but you must know the number at runtime
to use a For...Next loop. You learned how to use Step to increment or decrement
the counter of a For...Next loop, and even how to exit a loop prematurely by using
Exit For.
In this hour, you also learned how to use the powerful Do...Loop. Do...Loop
enables you to create flexible loops that can handle almost any looping scenario.
Depending on your needs, you can evaluate an expression in a Do...Loop by using
While or Until. You learned how evaluating expression on the Do statement makes
the loop behave differently than does evaluating on the Loop statement. If a
For...Next loop can’t do the job, some form of the Do...Loop will.
In addition to learning the specifics about loops, you’ve seen firsthand how multiple
solutions to a problem can exist. Often, one approach is clearly superior to all other
approaches, although you might not always find it. Other times, one approach
might be only marginally superior, or multiple approaches might all be equally
applicable. Expert programmers consistently find the best approaches to any given
problem. With time, you’ll be able to do the same.
Q&A
Q. Are there any specific cases in which one loop is more appropriate than
another?
Workshop 321
A. Usually, when you have to walk an index or sequential set of elements (such as
referencing all elements in an array), the For...Next loop is the best choice.
Q. Should I be concerned about the performance differences between the two
types of loops?
A. With today’s fast processors, chances are good that the performance difference
between the two loop types in any given situation will be overshadowed by the
readability and functionality of the best choice of loop. If you have a situation
in which performance is critical, write the loop in every way you can think of,
benchmark the results, and choose the fastest loop.
Workshop
Quiz
1. What keyword do you use to increment the counter variable in a For...Next
loop by a value other than 1?
2. True or false: You have to know the start and end values of a For...Next loop
at design time to use this type of loop.
3. What statement is used to close a loop started with a For statement?
4. Is it possible to nest loops?
5. What type of loop do you most likely need to create if you don’t have any idea
how many times the loop must occur?
6. If you evaluate the expression in a Do...Loop on the Loop statement, is it possible
that the code within the loop might never execute?
7. What statement do you use to terminate a Do...Loop without evaluating the
expression on the Do or Loop statement?
322 HOUR 14: Looping for Efficiency
Answers
1. Step
2. False. You have to know the values only at runtime.
3. Next
4. Yes!
5. A Do loop
6. No. The code always executes at least once.
7. Exit Do
Exercises
1. Create a text box in your No Remainders project, and let the user enter a number.
Find the first 10 numbers that are evenly divisible by the number the user
enters.
2. Use two For...Next loops nested within each other to size a label in two
dimensions. Have the outer loop change the label’s Width property from 1 to
100, and have the inner loop change the Height property from 1 to 100. Don’t
be surprised by the end result—it’s rather odd.
323
HOUR 15
Debugging Your Code
What You’ll Learn in This Hour:
. Adding comments to your code
. Identifying the two basic types of errors
. Working with break points
. Using the Immediate window
. Creating a structured error handler
No one writes perfect code. You’re most certainly familiar with those problems that
prevent code from executing properly—they’re called bugs. Because you’re new to
Visual Basic, your code will probably contain a fair number of bugs. As you gain proficiency,
the number of bugs in your code will decrease, but they will never disappear
entirely. This book can’t teach you how to debug every possible build or runtime
error you might encounter; debugging is a skill and an art. In this hour you will learn
the basic skills necessary to trace and correct most bugs in your code.
Before proceeding, create a new Windows Application project named Debugging
Example. Next, follow these steps to build the project:
1. Right-click Form1.vb in the Solution Explorer, choose Rename, and change the
form’s name to DebuggingExampleForm.vb. Next, set the form’s Text property
to Debugging Example (you will need to click the form to access its design
properties).
2. Add a new text box to the form by double-clicking the TextBox item in the
toolbox. Set the text box’s properties as follows:
Property Value
Name txtInput
Location 79, 113
Size 120, 20
324 HOUR 15: Debugging Your Code
3. Add a new button to the form by double-clicking the Button item in the toolbox,
and set its properties as follows:
Your form should now look like the one shown in Figure 15.1.
This little project will divide 100 by whatever is entered into the text box. As you
write the code to accomplish this, various bugs will be introduced on purpose, and
you’ll learn to correct them. Save your project now by clicking the Save All button on
the toolbar.
Property Value
Name btnPerformDivision
Location 79, 139
Size 120, 23
Text Perform Division
FIGURE 15.1
This simple interface
will help you
learn debugging
techniques.
Adding Comments to Your Code
One of the simplest things you can do to reduce bugs from the beginning—and to
make tracking down existing bugs easier—is to add comments to your code. A code
comment is simply a line of text that Visual Basic knows isn’t actual code and therefore
ignores. Comment lines are stripped from the code when the project is compiled
to create a distributable component, so comments don’t affect performance. Visual
Basic’s code window shows comments as green text. This makes it easier to read and
understand procedures. Consider adding comments to the top of each procedure,
stating the procedure’s purpose. In addition, you should add liberal comments
throughout all procedures, detailing what’s occurring in the code.
Adding Comments to Your Code 325
Comments are meant to be read by humans, not by computers. Strive to make
your comments intelligible. Keep in mind that a comment that’s difficult to understand
isn’t much better than no comment at all. Also remember that comments
serve as a form of documentation. Just as documentation for an application must
be clearly written, code comments should also follow good writing principles.
Did you
Know?
To create a comment, precede the comment text with the apostrophe character (’). A
simple comment might look like this, for example:
’ This is a comment because it is preceded with an apostrophe.
Comments can also be placed at the end of a line of code:
Dim intAge as Integer ‘ Used to store the user’s age in years.
Everything to the right of (and including) the apostrophe in this statement is a comment.
By adding comments to your code procedures, you don’t have to rely on memory
to decipher a procedure’s purpose or mechanics. If you’ve ever had to go back
and work with code you haven’t looked at in a while, or you’ve had to work with
someone else’s code, you probably already have a great appreciation for comments.
Double-click the Perform Division button now to access its Click event, and add the
following two lines of code (comments, actually):
’ This procedure divides 100 by the value entered in
‘ the text box txtInput.
Notice that after you type the ’ character, the comment text turns green.
When creating code comments, do your best to do the following:
. Document the code’s purpose (the why, not the how).
. Clearly indicate the thinking and logic behind the code.
. Call attention to important turning points in the code.
. Reduce the need for readers to run a simulation of the code execution in their
heads.
. Comment your code as you are typing it. If you wait until the code is complete,
you probably won’t go back and add comments.
326 HOUR 15: Debugging Your Code
Identifying the Two Basic Types of
Errors
Two types of errors can occur in code: build errors and runtime errors. A build error is a
coding error that prevents Visual Basic’s compiler from being able to process the code;
Visual Basic won’t compile a project that has a build error in it. A statement that calls
a procedure with incorrect parameters, for example, generates a build error. Runtime
errors are those that don’t occur at compile time but are encountered when the project
is being run. Runtime errors are usually a result of trying to perform an invalid
operation on a variable.
To illustrate, consider this next statement, which wouldn’t generate a compile error:
intResult = 10 / intDenominator
Under most circumstances, this code wouldn’t even generate a runtime error. However,
what happens if the value of intDenominator is 0? Ten divided by 0 is undefined,
which doesn’t fit into intResult (intResult is an Integer variable).
Attempting to run the code with the intDenominator variable having a value of 0
causes Visual Basic to return a runtime error. A runtime error is called an exception,
and when an exception occurs, it’s said to be thrown (that is, Visual Basic throws an
exception when a runtime error occurs). When an exception is thrown, code execution
stops at the offending statement, and Visual Basic displays an error message. You
can prevent Visual Basic from stopping execution when an exception is thrown by
writing special code to handle the exception, which you’ll learn about later in this
hour.
Add the following statements to the Click event, right below the two comment lines:
Dim lngAnswer As Long
lngAnswer = 100 / CLng(txtInput.Text)
MessageRox.Show(“100/” & txtInput.Text & “ is “ & lngAnswer)
The misspelling of the function name MessageBox is intentional; type in the preceding
line of code exactly as it appears. Although you’ve misspelled the function name,
Visual Basic doesn’t return an immediate error. Notice, however, that Visual Basic displays
a wavy blue line under the function name. Move the mouse pointer over the
underlined text, and leave it there for a second; Visual Basic displays a tip explaining
the nature of the error, as shown in Figure 15.2.
Press F5 to run the project. When you do, Visual Basic displays a message that a build
error was found, and it asks whether you want to continue by running the last successful
build. Because the code won’t run as is, there’s no point in continuing, so click
No to return to the code editor. Take a look at the Error List (if it’s not displayed, use
Identifying the Two Basic Types of Errors 327
FIGURE 15.2
Visual Basic
highlights build
errors in the
code window by
using wavy
lines.
the View menu to show it). All build errors in the current project appear in the Error
List, as shown in Figure 15.3. To view a particular offending line of code, double-click
an item in the Error List.
FIGURE 15.3
Build errors are
easy to find
using the Error
List.
328 HOUR 15: Debugging Your Code
Build errors are very serious because they prevent code from being compiled and
therefore prevent execution. Build errors must be corrected before you can run the
project. Double-click the build error in the Error List to go directly to the error.
Correct the problem by changing the R to a B so that the function name is
MessageBox. After you’ve made this change, press F5 to run the project. Visual Basic
no longer returns a build error; you’ve just successfully debugged a problem!
Click the Perform Division button now, and you’ll receive another error (see Figure
15.4).
This time the error is a runtime error, or exception. If an exception occurs, you know
that the code compiled without a problem because build errors prevent code from
compiling and executing. This particular exception is an Invalid Cast exception.
Invalid Cast exceptions generally occur when you attempt to perform a function
using a variable, but the variable is of an incompatible data type for the specified
operation. Note that Visual Basic highlights the offending statement with a yellow
background and a yellow arrow.
At this point, you know that the statement has a bug, and you know it’s related to
data typing. Choose Debug, Stop Debugging now to stop the running project and
return to the code editor.
FIGURE 15.4
A runtime exception
halts code
execution at the
offending line.
Using Visual Basic’s Debugging Tools 329
Using Visual Basic’s Debugging Tools
Visual Basic includes a number of debugging tools to help you track down and eliminate
bugs. In this section, you’ll learn how to use break points and the Immediate
window—two tools that form the foundation of any debugging arsenal.
Working with Break Points
Just as an exception halts the execution of a procedure, you can deliberately stop execution
at any statement of code by creating a break point. When Visual Basic encounters
a break point while executing code, execution is halted at the break statement
before the statement is executed. Break points enable you to query or change the
value of variables at a specific instance in time, and they let you step through code
execution one line at a time.
You’ll create a break point to help troubleshoot the exception in your lngAnswer =
statement.
Adding a break point is simple. Just click in the gray area to the left of the statement
at which you want to break code execution. When you do so, Visual Basic displays a
red circle, denoting a break point at that statement (see Figure 15.5). To clear the
break point, you click the red circle (but don’t do this now).
FIGURE 15.5
Break points
give you control
over code execution.
330 HOUR 15: Debugging Your Code
Break points are saved with the project. You don’t have to reset all your break
points each time you open the project.
By the
Way
Click the gray area to the left of the lngAnswer = statement to create a break point,
as shown in Figure 15.5. After you’ve set the break point, press F5 to run the program.
Click the Perform Division button again. When Visual Basic encounters the break
point, code execution is halted—right before the statement with the break point executes—
and the procedure with the break point is shown. In addition, the cursor is
conveniently placed at the statement with the current break point. Notice the yellow
arrow overlaying the red circle of the break point (see Figure 15.6). This yellow arrow
marks the next statement to be executed. It just so happens that the statement has a
break point, so the yellow arrow appears over the red circle. (The yellow arrow isn’t
always over a red circle, but it always appears in the gray area aligned with the next
statement that will execute.)
When code execution is halted at a break point, you can do a number of things.
Table 15.1 lists the most common actions. For now, press F5 to continue program execution.
Again, you get an overflow exception.
FIGURE 15.6
A yellow arrow
denotes the next
statement to be
executed.
Using Visual Basic’s Debugging Tools 331
Using the Immediate Window
Break points themselves aren’t usually sufficient to enable you to debug a procedure.
In addition to break points, you’ll often use the Immediate window to debug code.
The Immediate window is a Visual Studio IDE window that generally appears only
when your project is in Run mode. If the Immediate window isn’t displayed, press
Ctrl+G to display it now. Using the Immediate window, you can type in code statements
that Visual Basic executes immediately (hence the name). You’ll use the Immediate
window now to debug the problem statement example.
Type the following statement into the Immediate window and then press Enter:
? txtinput.text
TABLE 15.1 Actions That Can Be Taken at a Break Point
Action Keystroke Description
Continue code F5 Continues execution at the current break
execution statement.
Step into F8 Executes the statement at the break point
and then stops at the next statement. If the
current statement is a function call, F8
enters the function and stops at the first
statement in the function.
Step over Shift+F8 Executes the statement at the break point
and then stops at the next statement. If the
current statement is a function call, the
function is run in its entirety; execution stops
at the statement following the function call.
Step out Ctrl+Shift+F8 Runs all the statements in the current
procedure and halts execution at the
statement following the one that called the
current procedure.
332 HOUR 15: Debugging Your Code
Although it isn’t intuitive, the ? character has been used in programming for many
years as a shortcut for the word “print.” The statement you entered simply prints the
contents of the Text property of the text box to the Immediate window.
Notice how the Immediate window displays ”” on the line below the statement you
entered. This indicates that the text box contains an empty string (also called a zerolength
string). The statement throwing the exception is attempting to use the CLng()
function to convert the contents of the text box to a Long. The CLng() function
expects data to be passed to it, yet the text box has no data. (The Text property is
empty.) Consequently, an overflow exception occurs because CLng() doesn’t know
how to convert “no data” to a number.
Generally, when you receive an overflow exception, you should look at any variables
or properties being referenced to ensure that the data they contain is
appropriate data for the statement throwing the exception. You’ll often find that
the code is trying to perform an operation that’s inappropriate for the data being
supplied.
By the
Way
You can do a number of things to prevent this error. The most obvious is to
ensure that the text box contains a value before attempting to use CLng(). You’ll do
this now.
Visual Basic supports on-the-fly code editing. This means that you can modify code
while debugging it; you do not have to stop the project to make changes and then
run it once more to test your changes.
Put the cursor at the end of the Dim statement and press Enter. Next, enter the following
code statements:
If txtInput.Text = ““ Then
Exit Sub
End If
Remember the yellow arrow used to show the next statement that will execute? It
indicates that if you continue code execution now, the statement that throws the
exception will run once more. You want the new statements to execute. Follow these
steps to designate the new code as the next code to be executed:
1. Click the yellow arrow and hold down the mouse button.
Using Visual Basic’s Debugging Tools 333
2. Drag the yellow arrow to the statement that begins with If txtInput.Text.
3. Release the mouse button.
Now the yellow arrow should indicate that the next statement to execute will be the
If statement, as shown in Figure 15.7.
Press F5 to continue running the project. This time, Visual Basic doesn’t throw an
exception, and it doesn’t halt execution at your break point, because the test you just
created caused code execution to leave the procedure before the statement with the
break point was reached.
Next, follow these steps:
1. Type your name into the text box and click the Perform Division button again.
Now that the text box is no longer empty, execution passes the statement with
the exit test and stops at the break point.
2. Press F5 to continue executing the code; again you’ll receive an exception. This
time, however, the exception is an invalid cast exception; this is different from
the exception thrown previously.
3. Press Ctrl+G to display the Immediate window, and type the following into the
Immediate window (be sure to press Enter when you’re finished):
? txtinput.text
FIGURE 15.7
You can manually
control the
flow of code
when
debugging.
334 HOUR 15: Debugging Your Code
The Immediate window prints your name.
Well, you eliminated the problem of not supplying any data to the CLng() function,
but something else is wrong.
Press F5 to continue executing the code, and take a closer look at the description of
the exception. Toward the bottom of the Exception window is the text “View Detail.”
Click this link now. Visual Basic displays a View Detail window with more information
about the exception, as shown in Figure 15.8.
The text in the View Detail window says: ”Conversion from string “your name”
to type ‘Long’ is not valid.” It apparently still doesn’t like what’s being passed
to the CLng() function.
By now, it might have occurred to you that there’s no logical way to convert alphanumeric
text to a number; CLng() needs a number to work with. You can easily test this
by following these steps:
1. Choose Debug, Stop Debugging.
2. Press F5 to run the project.
3. Enter a number into the text box, and click the button. Code execution again
stops at the break point.
4. Press F8 to execute the statement. No errors this time! Press F5 to continue execution;
Visual Basic displays the message box (finally). Click OK to dismiss the
message box, and then close the form to stop the project.
Did you You can use the Immediate window to change the value of a variable.
Know?
Because the CLng() function expects a number, but the text box contains no intrinsic
way to force numeric input, you have to accommodate this situation in your code.
FIGURE 15.8
The View Detail
window gives
you important
information for
fixing exception
problems.
Using Visual Basic’s Debugging Tools 335
Visual Basic includes a handy function called IsNumeric, which returns True if the
supplied argument is a number and False if not. You can use this function to ensure
that only a number is passed to the CLng() function. Add the following statement
immediately below the last If...Then construct you entered (after the End...If
statement):
If Not (IsNumeric(txtInput.Text)) Then Exit Sub
This statement simply passes the contents of the text box to the IsNumeric() function.
If the function returns False (the text is not a number), the procedure is exited.
Your procedure should now look similar to the one shown in Figure 15.9. Realize that
the first If...End If statement is redundant; the new statement will catch when a
user hasn’t entered anything into the text box.
Go ahead and press F5 to run the project. Enter some nonnumeric text into the text
box and click the button. If you entered the code correctly, no exception occurs; the
data validation tests you’ve created prevent inappropriate data from being passed to
the CLng() function. You just debugged the procedure!
The Immediate window is a powerful debugging tool. You can use it to get and set
variables as well as view the value in a property. You can even use the Immediate
window to call functions. For example, while in Break mode, you could enter the following
into the Immediate window, and Visual Basic would print the result of the
function call:
? IsNumeric(txtInput.Text)
FIGURE 15.9
The final code,
complete with
data verification.
336 HOUR 15: Debugging Your Code
You can even use the Immediate window to print data from within code during
debugging. To do so, you use the WriteLine()method of the Debug object, like this:
Debug.WriteLine(lngInteger1 + lngInteger2)
Whatever you place within the parentheses of the Debug.WriteLine() method gets
printed to the Immediate window. Note that you can print literal text, numbers, variables,
and expressions. Debug.WriteLine() is most useful in cases where you want
to know the value of a variable, but you don’t want to halt code execution using a
break point. For example, suppose that you had a number of statements that manipulate
a variable. You could sprinkle Debug.WriteLine() statements into the code to
print the variable’s contents at strategic points. When you do this, you’ll want to print
some text along with the variable’s value so that the output makes sense to you. For
example:
Debug.WriteLine(“Results of area calculation = “ & sngArea)
You can also use Debug.WriteLine to create checkpoints in your code, like this:
Debug.WriteLine(“Passed Checkpoint 1”)
‘ Execute statement here
Debug.WriteLine(“Passed Checkpoint 2”)
‘ Execute another statement here
Debug.WriteLine(“Passed Checkpoint 3”)
Many creative uses exist for the Immediate window, and you should get comfortable
using it; it’ll help you through many tough debugging sessions. Just remember that
the Immediate window isn’t available to a compiled component; the compiler ignores
calls to the Debug object when creating distributable components.
Writing an Error Handler Using
Try...Catch...Finally
It’s useful to have Visual Basic halt execution when an exception occurs. When the
code is halted while running in the IDE, you receive an error message, and you’re
shown the offending line of code. However, when your project is run as a compiled
program, an unhandled exception causes the program to terminate (crash to the
desktop). This is one of the most undesirable things an application can do. Fortunately,
you can prevent exceptions from stopping code execution (and terminating
compiled programs) by writing code specifically designed to deal with exceptions.
Exception-handling code instructs Visual Basic on how to deal with an exception
instead of relying on Visual Basic’s default behavior of aborting the application.
Writing an Error Handler Using Try...Catch...Finally 337
Visual Basic supports unstructured error handling in the way of On Error statements.
This method of handling errors, although still supported by Visual Basic, is
now considered antiquated. You might encounter procedures that use this form of
error handling in legacy or sample code, but Microsoft strongly recommends that
you use the Try...Catch...Finally structure for dealing with exceptions in all
new code.
By the
Way
Visual Basic supports structured error handling (a formal way of dealing with errors) in
the form of the Try...Catch...Finally structure. Creating structured errorhandling
code can be a bit confusing at first, and, like most coding principles, it’s
best understood when you do it.
Create a new Windows Application called Structured Exception Handling, and follow
these steps to build the project:
1. Right-click Form1.vb in the Solution Explorer, choose Rename, and change the
name of the default form to ExceptionHandlingExampleForm.vb. Next, set
the form’s Text property to Structured Exception Handling.
2. Add a new button to the form, and set its properties as follows:
Property Value
Name btnCatchException
Location 93, 128
Size 96, 23
Text Catch Exception
Double-click the button, and add the following code. Be aware that when you enter
the Try statement, Visual Basic automatically creates the End Try and Catch ex As
Exception statements.
Try
Debug.WriteLine(“Try”)
Catch ex As Exception
Debug.WriteLine(“Catch”)
Finally
Debug.WriteLine(“Finally”)
End Try
Debug.WriteLine(“Done Trying”)
As you can see, the Try...End Try structure has starting and ending statements,
much like loops and decision constructs. The Try...End Try structure is used to
wrap code that might cause an exception and provides you the means of dealing
with thrown exceptions. Table 15.2 explains the parts of this structure.
338 HOUR 15: Debugging Your Code
Press F5 to run the project, and then click the button. Next, take a look at the contents
of the Immediate window (Ctrl+G). The Immediate window should contain the
following lines of text:
Try
Finally
Done Trying
Here’s what happened:
1. The Try block begins, and code within the Try section executes.
2. Because no exception occurs, code within the Catch section is ignored.
3. When all statements within the Try section finish executing, the code within
the Finally section executes.
4. When all statements within the Finally section finish executing, execution
jumps to the statement immediately following End Try.
Stop the project now by choosing Debug, Stop Debugging.
Now that you understand the basic mechanics of the Try...End Try structure, you’ll
add statements within the structure so that an exception occurs and gets handled.
TABLE 15.2 Sections of the Try...End Try Structure
Section Description
Try The Try section is where you place code that might cause an
exception. You can place all of a procedure’s code within the Try
section, or just a few lines.
Catch Code within the Catch section executes only when an exception
occurs; it’s the code you write to catch the exception.
Finally Code within the Finally section occurs when the code within the
Try and/or Catch sections completes. This section is where you
place your cleanup code—code that you always want executed,
regardless of whether an exception occurs.
Writing an Error Handler Using Try...Catch...Finally 339
Change the contents of the procedure to match this code:
Dim lngNumerator As Long = 10
Dim lngDenominator As Long = 0
Dim lngResult As Long
Try
Debug.WriteLine(“Try”)
lngResult = lngNumerator / lngDenominator
Catch ex As Exception
Debug.WriteLine(“Catch”)
Finally
Debug.WriteLine(“Finally”)
End Try
Debug.WriteLine(“Done Trying”)
Again, press F5 to run the project. Click the button, and take a look at the Immediate
window. This time, the text in the Immediate window should read
Try
A first chance exception of type ‘System.OverflowException’ _
occurred in Structured Exception Handling.EXE
Catch
Finally
Done Trying
Notice that this time the code within the Catch section executes. That’s because the
statement that sets lngResult causes an overflow exception. Had this statement not
been placed within a Try block, Visual Basic would have raised the exception, and an
error dialog box would’ve appeared. However, because the statement is placed within
the Try block, the exception is caught. Caught means that when the exception
occurred, Visual Basic directed execution to the Catch section. (You do not have to use
a Catch section. If you omit a Catch section, caught exceptions are simply ignored.)
Notice also how the code within the Finally section executes after the code within
the Catch section. Remember that code within the Finally section always executes,
regardless of whether an exception occurs.
Dealing with an Exception
Catching exceptions so that they don’t crash your application is a noble thing to do,
but it’s only part of the error-handling process. You’ll usually want to tell the user (in
a friendly way) that an exception has occurred. You’ll probably also want to tell the
user what type of exception occurred. To do this, you must have a way of knowing
what exception was thrown. This is also important if you intend to write code to deal
with specific exceptions. The Catch statement enables you to specify a variable to
hold a reference to an Exception object. Using an Exception object, you can get
340 HOUR 15: Debugging Your Code
information about the exception. The following is the syntax used to place the exception
in an Exception object:
Catch variablename As Exception
Modify your Catch section to match the following:
Catch ex As Exception
Debug.WriteLine(“Catch”)
MessageBox.Show(“An error has occurred: “ & ex.Message)
The Message property of the Exception object contains the text that describes the
specific exception that occurred. Run the project and click the button. Visual Basic
displays your custom error message, as shown in Figure 15.10.
Like other code structures, Visual Basic has a statement that can be used to exit
a Try...End Try structure at any time: Exit Try. Note, however, that if you use
Exit Try, code jumps to the Finally section and then continues with the statement
immediately following the End Try statement.
By the
Way
Handling an Anticipated Exception
At times, you’ll anticipate a specific exception being thrown. For example, you might
write code that attempts to open a file when the file does not exist. In such an
FIGURE 15.10
Structured
exception handling
enables
you to decide
what to do when
an exception
occurs.
Writing an Error Handler Using Try...Catch...Finally 341
instance, you’ll probably want the program to perform certain actions when this
exception is thrown. When you anticipate a specific exception, you can create a
Catch section designed specifically to deal with that one exception.
Recall from the previous section that you can retrieve information about the current
exception by using a Catch statement, such as
Catch objException As Exception
By creating a generic Exception variable, this Catch statement catches any and all
exceptions thrown by statements within the Try section. To catch a specific exception,
change the data type of the exception variable to a specific exception type.
Remember the code you wrote earlier that caused a System.InvalidCastException
when an attempt was made to pass an empty string to the CLng() function? You
could have used a Try...End Try structure to deal with the exception, using code
such as this:
Dim lngAnswer As Long
Try
lngAnswer = 100 / CLng(txtInput.Text)
MessageBox.Show(“100/” & txtInput.Text & “ is “ & lngAnswer)
Catch objException As System.InvalidCastException
MessageBox.Show(“You must enter something in the text box.”)
Catch objException As Exception
MessageBox.Show(“Caught an exception that wasn’t an invalid cast.”)
End Try
Notice that this structure has two Catch statements. The first Catch statement is
designed to catch only an overflow exception; it doesn’t catch exceptions of any
other type. The second Catch statement doesn’t care what type of exception is
thrown; it catches all of them. The second Catch statement acts as a catchall for any
exceptions that aren’t overflow exceptions because Catch sections are evaluated
from top to bottom, much as Case statements are in the Select...Case structure.
You could add more Catch sections to catch other specific exceptions if the situation
calls for it.
In this next example, you’ll build on the Picture Viewer project last edited in Hour
11, “Using Constants, Data Types, Variables, and Arrays,” so go ahead and open that
project now. First, I want you to see the exception that you’ll catch. Follow these steps
to cause an exception to occur:
1. Press F5 to run the project.
2. Click the Open Picture button on the toolbar to display the Select Picture dialog
box.
342 HOUR 15: Debugging Your Code
3. In the File Name: box, enter *.* and press Enter. This changes your filter so that
you can now select files that aren’t images. Locate a file on your hard drive
that you know is not an image. Files with the extension .txt, .ini, or .pdf
are perfect.
4. After you’ve located a file that isn’t an image file, click it to select it, and then
click Open.
You have caused an out-of-memory exception, as shown in Figure 15.11. This is the
exception thrown by the picture box when you attempt to load a file that isn’t a picture.
Your first reaction might be something along the lines of “Why do I have to
worry about that? No one would do that.” Well, welcome to programming, my
friend! A lot of your time will be spent writing code to protect users from themselves.
It’s not fair and usually not fun, but it is a reality.
Go ahead and click Stop Debugging on the toolbar to stop the running project.
Rather than take you step by step through the changes, it’s easier to just show you
the code for the new OpenPicture() procedure. Change your code to make the code
shown here:
Try
‘ Show the open file dialog box.
If ViewerForm.ofdSelectPicture.ShowDialog = DialogResult.OK Then
‘ Load the picture into the picture box.
FIGURE 15.11
You never want
an unhandled
exception to
occur—ever.
Writing an Error Handler Using Try...Catch...Finally 343
ViewerForm.picShowPicture.Image = _
Image.FromFile(ViewerForm.ofdSelectPicture.FileName)
‘ Show the name of the file in the statusbar.
ViewerForm.sbrMyStatusStrip.Items(0).Text = _
ViewerForm.ofdSelectPicture.FileName
End If
Catch objException As System.OutOfMemoryException
MessageBox.Show(“The file you have chosen is not an image file.”, _
“Invalid File”, MessageBoxButtons.OK)
End Try
What you’ve just done is wrapped the procedure in an error handler that watches for
and deals with an out-of-memory exception. Press F5 to run the project, and follow
the steps outlined earlier to load a file that isn’t an image. Now, rather than receiving
an exception from the IDE, your application displays a custom message box that
is much more user-friendly and that won’t crash the application to the desktop (see
Figure 15.12)!
Although you have eliminated the possibility of the user’s generating an out-ofmemory
exception by choosing a file that isn’t a valid picture, you should be aware
of some caveats regarding the code changes you made:
. If some other code in the procedure caused an out-of-memory exception, you
would be misleading the user with your error message. You could address this
FIGURE 15.12
A useful message
is much
better than an
unhandled
exception.
344 HOUR 15: Debugging Your Code
by wrapping only the statement in a question within its own Try...End Try
structure.
. If an exception of another type is encountered in the procedure, that error is
ignored. You can prevent this by creating a generic Catch block to catch any
additional exceptions.
As you can see, the mechanics of adding a Try...End Try structure to handle
exceptions is relatively easy, whereas knowing what specifically to catch and how to
handle the situation when an exception is caught can prove to be challenging.
Summary
In this hour, you learned the basics of debugging applications. You learned how
adding useful and plentiful comments to your procedures makes debugging easier.
However, no matter how good your comments are, you’ll still have bugs.
You learned about the two basic types of errors: build errors and runtime errors
(exceptions). Build errors are easier to troubleshoot because the compiler tells you
exactly what line contains a build error and generally provides useful information
about how to correct it. Exceptions, on the other hand, can crash your application if
not handled properly. You learned how to track down exceptions, using break points
and the Immediate window. Finally, you learned how to make your applications
more robust by using the Try...End Try structure to create structured error handlers.
No book can teach you everything you need to know to write bug-free code. However,
this hour taught you the basic skills you need to track down and eliminate many
types of errors in your programs. As your skills as a programmer improve, so will
your debugging abilities.
Q&A
Q. Should I alert the user that an exception has occurred or just let the code
keep running?
A. If you’ve written code to handle the specific exception, there’s probably no
need to tell the user about it. However, if an exception occurs that the code
doesn’t know how to address, you should provide the user with the exception
information so that he or she can report the problem accurately and you can
fix it.
Workshop 345
Q. Should I comment every statement in my application?
A. Probably not. However, consider commenting every decision-making and looping
construct in your program. Such sections of code are usually pivotal to the
procedure’s success, and what they do isn’t always obvious.
Workshop
Quiz
1. What type of error prevents Visual Basic from compiling and running code?
2. What is another name for a runtime error?
3. What character is used to denote a comment?
4. To halt execution at a specific statement in code, what do you set?
5. Explain the yellow arrow and red circles that can appear in the gray area in
the code editor.
6. What IDE window would you use to poll the contents of a variable in break
mode?
7. True or false: You must always specify a Catch section in a Try...End Try
structure.
Answers
1. A build error
2. An exception
3. The apostrophe (’)
4. A break point
5. The yellow arrow denotes the next statement to be executed during debugging.
The red circles denote break points—statements where code execution halts
when reached.
6. The Immediate window
7. False. If you omit a Catch section, the exception is ignored.
346 HOUR 15: Debugging Your Code
Exercises
1. In the code example that sets lngAnswer to the result of a division expression,
change lngAnswer from a Long to a Single (call it sngAnswer). Next, remove
the If statements that test the contents of the text box before performing the
division. Do you get the same two exceptions that you did when the variable
was a Long? Why or why not?
2. Rewrite the code that sets lngAnswer to the result of a division expression so
that the code is wrapped in a Try...End Try structure. Remove the If statements
that perform data validation, and create Catch sections for the exception
that might be thrown.
347
HOUR 16
Designing Objects Using
Classes
What You’ll Learn in This Hour:
. Encapsulating data and code using classes
. Comparing classes to standard modules
. Creating an object interface
. Exposing object attributes as properties
. Exposing functions as methods
. Instantiating objects from classes
. Binding an object reference to a variable
. Releasing object references
. Understanding object lifetimes
You learned about what makes an object an object in Hour 3, “Understanding
Objects and Collections.” Since that hour, you’ve learned how to manipulate objects
such as forms and controls. The real power of leveraging objects, however, comes
from being able to design and implement custom objects of your own. In this hour,
you’ll learn how to create your own objects by using classes (in contrast to using
standard modules). You’ll learn how to define the template for an object and how to
create your own custom properties and methods.
348 HOUR 16: Designing Objects Using Classes
By the
Way There is simply no way to become an expert on programming classes in a single
hour. However, when you’ve finished with this chapter, you’ll have working knowledge
of creating classes and deriving custom objects from those classes; consider
this hour a primer on object-oriented programming. I strongly encourage you
to seek out other texts that focus on object-oriented programming after you feel
comfortable with the material presented in this book.
Understanding Classes
Classes enable you to develop applications using object-oriented programming
(OOP) techniques (recall that I discussed OOP briefly in Hour 3). Classes are templates
that define objects. Although you might not have known it, you’ve been
programming with classes throughout this book. When you create a new form in a
Visual Basic project, you’re actually creating a class that defines a form; forms
instantiated at runtime are derived from the class. Using objects derived from predefined
classes (such as the Visual Basic Form class) is just the start of enjoying the
benefits of object-oriented programming. To truly realize the benefits of OOP, you
must create your own classes.
The philosophy of programming with classes is considerably different from that of
traditional programming. Proper class-programming techniques can make your
programs better, in both structure and in reliability. Class programming forces you
to consider the logistics of your code and data more thoroughly, causing you to
create more reusable and extendable object-based code.
Encapsulating Data and Code Using Classes
An object derived from a class is an encapsulation of data and code—that is, the
object comprises its code and all the data it uses. Suppose that you need to keep
track of employees in an organization, for example, and that you must store
many pieces of information for each employee, such as name, date hired, and
title. In addition, suppose that you need methods for adding and removing
employees, and that you want all this information and functionality available to
many functions within your application. You could use standard modules to
manipulate the data, but doing so would most likely require many variable arrays
as well as code to manage those arrays.
A better approach is to encapsulate all the employee data and functionality
(adding and deleting routines and so forth) into a single, reusable object. Encapsulation
is the process of integrating data and code into one entity: an object. Your
Understanding Classes 349
application, as well as external applications, could then work with the employee
data through a consistent interface—the Employee object’s interface. (An interface
is a set of exposed functionality—essentially, code routines that define methods,
properties, and events.)
The encapsulation of data and code is the key idea of classes. By encapsulating the
data and the routines to manipulate the data into a single object by way of a
class, you free application code that needs to manipulate the data from the intricacies
of data maintenance. For example, suppose that company policy has
changed so that when a new employee is added to the system, a special tax record
must be generated and a form must be printed. If the data and code routines
weren’t encapsulated in a common object but instead were written in various
places throughout your code, you would have to modify every module that contained
code to create a new employee record. By using a class to create an object,
you need to change the code in only one location: within the class. As long as you
don’t modify the object’s interface (as discussed shortly), all the routines that use
the object to create a new employee will instantly have the policy change in effect.
Comparing Classes with Standard Modules
Classes are similar to standard modules in how they appear in the Visual Studio
design environment and in how you write code within them. However, the behavior
of classes at runtime differs greatly from that of standard modules. With a
standard module, all module-level data (static and module-level variables) is
shared by all procedures within the module. In addition, there are never multiple
instances of the module data. With classes, objects are instantiated from a class,
and each object receives its own set of module data.
As you learned in Hour 11, “Using Constants, Data Types, Variables, and Arrays,”
module-level variables in a standard module exist for the lifetime of the application.
However, module variables for a class exist only for the duration of an
object’s lifetime. Objects can be created and destroyed as needed, and when an
object is destroyed, all its data is destroyed as well.
Classes differ from standard modules in more ways than just how their data
behaves. When you define a standard module, its public functions and procedures
are instantly available to other modules within your application. However, public
functions and procedures of classes aren’t immediately available to your program.
Classes are templates for objects. At runtime, your code doesn’t interact with the
code in the class module per se, but it instantiates objects derived from the class.
Each object acts as its own class “module” and thus has its own set of module
350 HOUR 16: Designing Objects Using Classes
data. When classes are exposed externally to other applications, the application
containing the class’s code is called the server. An application that creates and uses
instances of an object is called a client. When you use instances of classes in the
application that contains those classes, the application itself acts as both a client
and a server. In this hour, I’ll refer to the code instantiating an object derived from
a class as client code.
Begin by creating a new Windows Application called Class Programming Example,
and then follow these steps to create your project:
1. Rename the default form ClassExampleForm.vb, and set its Text property
to Class Programming Example.
2. Add a new class to the project by choosing Project, Add Class. Save the class
with the name clsMyClass.vb, as shown in Figure 16.1.
FIGURE 16.1
Classes are
added to a project
just as other
object files are
added.
Creating an Object Interface
For an object to be created from a class, the class must expose an interface. As I
mentioned earlier, an interface is a set of exposed functionality (properties, methods,
and events). An interface is the means by which client code communicates
with the object derived from the class. Some classes expose a limited interface, and
others expose complex interfaces. The content and quantity of your class’s interface
are entirely up to you.
Understanding Classes 351
A class interface consists of one or more of the following members:
. Properties
. Methods
. Events
For example, assume that you’re creating an Employee object (that is, a class used to
derive employee objects). You must first decide how you want client code to interact
with your object. You’ll want to consider both the data contained within the object
and the functions that the object can perform. You might want client code to be able
to retrieve the name of an employee and other information such as sex, age, and the
date of hire. For client code to get these values from the object, the object must
expose an interface member for each of these items. You’ll recall from Hour 3 that
values exposed by an object are called properties. Therefore, each piece of data discussed
here would have to be exposed as a property of the Employee object.
In addition to properties, you can expose functions, such as Delete or AddNew. These
functions may be simple or complex. The Delete function of the Employee object, for
example, might be complex. It would need to perform all the actions necessary to
delete an employee, including such things as removing the employee from an
assigned department, notifying the accounting department to remove the employee
from the payroll, notifying the security department to revoke the employee’s security
access, and so on. Publicly exposed functions of an object, as you should again
remember from Hour 3, are called methods.
Properties and methods are the most commonly used interface members. Although
designing properties and methods might be new to you, by now using them isn’t.
You’ve used properties and methods in almost every hour so far. Here, you’ll learn
the techniques for creating properties and methods for your own objects.
For even more interaction between the client and the object, you can expose custom
events. Custom object events are similar to the events of a form or text box. However,
with custom events, you have complete control over the following:
. The name of the event
. The parameters passed to the event
. When the event occurs
Creating custom events is complicated, and I’ll cover only custom properties and
methods in this hour.
By the
Way
352 HOUR 16: Designing Objects Using Classes
Properties, methods, and events together make up an object’s interface. This interface
acts as a contract between the client application and the object. Any and all communication
between the client and the object must transpire through this interface, as
shown in Figure 16.2.
Luckily, Visual Basic handles the technical details of the interaction between the client
and the object by way of the interface. Your responsibility is to define an object’s properties,
methods, and events so that its interface is logical and consistent and exposes
all the functionality a client must have available to use the object productively.
Exposing Object Attributes as Properties
Properties are the attributes of objects. Properties can be read-only, or they can allow
both reading and writing of their values. For example, you might want to let a client
retrieve the value of a property containing the path of the component but not let the
client change it because the path of a running component can’t be changed.
You can add properties to a class in two ways. The first is to declare public variables.
Any variable declared as public instantly becomes a property of the class (actually, it
acts like a property, but it isn’t technically a property it is a field). For example, suppose
that you have the following statement in the Declarations section of a class:
Public Quantity as Integer
Clients could read from and write to the field, using code like the following:
objMyObject.Quantity = 420
This works, but significant limitations exist that make this approach less than desirable:
. You can’t execute code when a field (“property”) value changes. For example,
what if you wanted to write the quantity change to a database? Because the
Client and Object Interaction
Object
Interface
Properties
Methods
Events
Client
FIGURE 16.2
Clients interact
with an object
via the object’s
interface.
Understanding Classes 353
client application can access the variable directly, you have no way of knowing
when the value of the variable changes.
. You can’t prevent client code from changing a field because the client code
accesses the variable directly.
. Perhaps the biggest problem is this: How do you control data validation? For
instance, how could you ensure that Quantity is never set to a negative value?
It’s simply not possible to work around these issues when using a public variable.
Instead of exposing public variables, you should use property procedures to create
class properties.
Property procedures enable you to execute code when a property is changed, to validate
property values, and to dictate whether a property is read-only, write-only, or
both readable and writable. Declaring a property procedure is similar to declaring a
standard Function or Sub procedure, but with some important differences. The basic
structure of a property procedure looks like this:
Public Property propertyname() As datatype
Get
‘ Code to return the property’s value goes here.
End Get
Set(ByVal Value As datatype)
‘ Code that accepts a new value goes here.
End Set
End Property
The first word in the property declaration simply designates the scope of the property
(usually Public, Private, or Friend). Properties declared with Public are available
to code outside the class. (They can be accessed by client code.) If the application
exposes its objects to other applications, Public procedures are visible outside the
application. Procedures declared as Friend, on the other hand, behave like Public
procedures, with the exception that they are not available outside the application.
Properties declared as Private are available only to code within the class. Immediately
following the scope identifier is the word Property. This word tells Visual Basic
that you’re creating a property procedure rather than a Sub or Function procedure.
Next come the property name and data type.
Type the following two statements into your class:
Private m_intHeight As Integer
Public Property Height() As Integer
After entering the statements, press Enter to commit them. Visual Basic fills in the rest
of the procedure template for you, as shown in Figure 16.3.
354 HOUR 16: Designing Objects Using Classes
You might be wondering why you just created a module-level variable of the same
name as your property procedure (with a naming prefix, of course). After all, I just
finished preaching about the problems of using a module-level variable as a property.
The reason is that a property has to get its value from somewhere, and a
module-level variable is usually the best place to store it. The property procedure acts
as a wrapper for this variable. Notice that the variable is declared as Private rather
than Public. This means that no code outside the class can view or modify the contents
of this variable; as far as client code is concerned, this variable doesn’t exist.
Between the property declaration statement and the End Property statement are two
constructs: Get and Set. These constructs are discussed next.
Creating Readable Properties Using the Get Construct The Get construct is
used to place code that returns a value for the property when read by a client.
Think of the Get construct as a function; whatever you return as the result of the
function becomes the property value. Add the following statement between the Get
and End Get statements:
Return m_intHeight
All this statement does is return the value of the variable m_intHeight when client
code requests the value of the Height property.
Creating Writable Properties Using the Set Construct The Set construct is
where you place code that accepts a new property value from client code.
FIGURE 16.3
Visual Basic creates
property
procedure templates.
Understanding Classes 355
Add the following statement between the Set and End Set statements:
m_intHeight = Value
If you look closely at the Set statement, you’ll see that it’s similar to a Sub declaration
and that Value is a parameter. Value contains the value being passed to the
property by the client code. The statement you just entered assigns the new value to
the module-level variable.
As you can see, the property procedure is a wrapper around the module-level variable.
When the client code sets the property, the Set construct stores the new value in
the variable. When the client retrieves the value of the property, the Get construct
returns the value in the module-level variable.
So far, the property procedure, with its Get and Set constructs, doesn’t do anything
different from what it would do if you were to simply declare a public variable (only
the property procedure requires more code). However, look at this variation of the
same Set construct:
Set(ByVal value As Integer)
If m_intHeight < 10 Then Exit Property
m_intHeight = value
End Set
This Set construct restricts the client to setting the Height property to a value greater
than or equal to 10. If a value less than 10 is passed to the property, the property procedure
terminates without setting m_intHeight. You’re not limited to performing
only data validation; you can pretty much add whatever code you want and even
call other procedures. Go ahead and add the verification statement to your procedure
so that the Set construct looks like this one. Your code should now look like the procedure
shown in Figure 16.4.
Creating Read-Only or Write-Only Properties There will be times that you will
want to create properties that can be read but not changed. Such properties are called
read-only properties. When discussing the fictitious Dog object in Hour 3, I talked
about creating a property called NumberOfLegs. With such an object, you might want
to expose the property as read-only—code can get the number of legs but cannot
change it. To create a read-only property, you would use the ReadOnly keyword to
declare the property procedure and then remove the Set...End Set section. For
example, if you wanted the property procedure you just created to define a read-only
procedure, you might declare it like this:
Public ReadOnly Property Height() As Integer
Get
Return m_intHeight
End Get
End Property
356 HOUR 16: Designing Objects Using Classes
FIGURE 16.4
This is a property
procedure,
complete with
data validation.
Although far more rare, it is possible to create a write-only property, in which the
property can be set but not read. To do so, you would use the keyword WriteOnly
in place of ReadOnly and remove the Get...End Get section instead of the
Set...End Set section.
Did you
Know?
Exposing Functions as Methods
Unlike a property that acts as an object attribute, a method is a function exposed by
an object. Methods are nothing more than exposed code routines. A method can
return a value, but it doesn’t have to. Methods are easier to create than properties
because they’re defined just as ordinary Sub and Function procedures are. To create a
method within a class, create a public Sub or Function procedure. Create the following
procedure in your class now (enter this code on the line following the End Property
statement):
Public Function AddTwoNumbers(ByVal intNumber1 As Integer, _
ByVal intNumber2 As Integer) As Long
AddTwoNumbers = intNumber1 + intNumber2
End Function
Like normal Sub and Function procedures, methods defined with Function return
values, whereas methods defined with Sub don’t. To make a procedure private to the
class and therefore invisible to client code, declare the procedure as Private rather
than Public.
Instantiating Objects from Classes 357
Instantiating Objects from Classes
After you obtain a reference to an object and assign it to a variable, you can manipulate
the object by using an object variable. Let’s do so now.
Click the ClassExampleForm.vb Design tab to view the Form Designer, and add a button
to the form by double-clicking the Button item in the toolbox. Set the button’s
properties as follows:
Property Value
Name btnCreateObject
Location 100, 120
Size 88, 23
Text Create Object
Next, double-click the button to access its Click event, and enter the following code:
Dim objMyObject As Object
objMyObject = New clsMyClass()
MessageBox.Show(objMyObject.AddTwoNumbers(1, 2))
The first statement creates a variable of type Object (dimension variables were discussed
in Hour 11). The second statement needs an explanation. Because the variable
appears on the left side of the equals sign, you can deduce that the variable is
being set to some value.
However, what appears on the right side of the equals sign might look foreign to you.
You want to place a reference to an object in the variable, but no object has yet been
created. The New keyword tells Visual Basic to create a new object, and the text following
New is the name of the class to use to derive the object (remember, classes are
object templates). The last statement calls the AddTwoNumbers method of your class
and displays the result in a message box.
Go ahead and run the project by pressing F5, and then click the button to make
sure that everything is working correctly. When finished, stop the project and save
your work.
Binding an Object Reference to a Variable
An object can contain any number of properties, methods, and events; every object is
different. When you write code to manipulate an object, Visual Basic has to understand
the object’s interface, or your code won’t work. The interface members (the
object’s properties, methods, and events) are resolved when an object variable is
358 HOUR 16: Designing Objects Using Classes
bound to an object. The two forms of binding are early binding, which occurs at compile
time, and late binding, which occurs at runtime. It’s important that you have at
least a working understanding of binding if you’re to create code based on classes.
Although I can’t explain the intricacies and technical details of early binding versus
late binding in this hour, I’ll teach you what you need to know to perform each type
of binding.
Both types of binding have advantages, but early binding generally is superior to
late binding. Code that uses late-bound objects requires more work by Visual
Basic than code that uses early-bound objects.
By the
Way
Late-Binding an Object Variable
When you dimension a variable as data type Object, as shown in the following code
sample, you’re late-binding to the object:
Dim objMyObject As Object
objMyObject = New clsMyClass()
MessageBox.Show(objMyObject.AddTwoNumbers(1, 2))
You cannot use late binding in a project with Option Strict turned on (refer to Hour
11 for information on Option Strict).
By the
Way
When you late-bind an object, the binding occurs at runtime when the variable is set
to reference an object. For a member of the object to be referenced, Visual Basic must
determine and use an internal ID of the specified member. Fortunately, because
Visual Basic handles all the details, you don’t need to know the ID of a member. Just
be aware that Visual Basic does need to know the ID of a member to use it. When
you late-bind an object variable (dimension the variable As Object), the following
occurs behind the scenes:
1. Visual Basic obtains a special ID (the Dispatch ID) of the property, method, or
event that you want to call. This takes time and resources.
2. An internal array containing the parameters of the member, if any, is created.
3. The member is invoked, using the ID obtained in step 1.
The preceding steps require a great deal of overhead and adversely affect an application’s
performance. Therefore, late binding isn’t the preferred method of binding.
Late binding does have some attractive uses, but most of them are related to using
objects outside your application, not to using objects derived from classes within the
project.
Instantiating Objects from Classes 359
One of the main drawbacks of late binding is the compiler’s inability to check the
syntax of the code manipulating an object. Because a member’s ID and the parameters
it uses aren’t determined until runtime, the compiler has no way of knowing
whether you’re using a member correctly—or even if the member you’re referencing
exists. This can result in a runtime exception or some other unexpected behavior.
Change the third statement in your code to look like the following (deliberately misspell
the AddTwoNumbers method):
MessageBox.Show(objMyObject.AddtoNumbers(1, 2))
Press F5 to run the project. No problems—well, so far, at least. Even though the
method name is misspelled, Visual Basic compiles the project without raising a build
error. This happens because the variable is declared As Object, and Visual Basic has
no idea what will eventually be placed in the variable. Therefore, it can’t perform
any syntax checking at compile time and just assumes that whatever action you perform
with the variable is correct. Click the button to create the object and call the
method. When you do, you get the exception shown in Figure 16.5.
As explained in Hour 15, “Debugging Your Code,” runtime exceptions are more
problematic than build errors because they’re usually encountered by end users and
under varying circumstances. When you late-bind objects, it’s easy to introduce these
types of problems; therefore, late binding has a real risk of throwing exceptions. As
you’ll see in the next section, early binding reduces many of these risks.
Go ahead and choose Debug, Stop Debugging before continuing.
FIGURE 16.5
Exceptions such
as this are a risk
of late binding.
360 HOUR 16: Designing Objects Using Classes
Early-Binding an Object Variable
If Visual Basic can determine a Dispatch ID for a member at compile time, there’s no
need to look up the ID when the member is referenced at runtime. This results in
considerably faster calls to object members. Not only that, but Visual Basic can also
validate the member call at compile time, reducing the chance of errors in your code.
Early binding occurs when you dimension a variable as a specific type of object,
rather than just As Object. When a variable is early-bound, Visual Basic looks up
the Dispatch IDs of the object’s members at compile time, rather than at runtime.
The following are important reasons to use early binding:
. Speed
. More speed
. Objects, their properties, and their methods appear in IntelliSense drop-down
lists.
. The compiler can check for syntax and reference errors in your code so that
many problems are found at compile time, rather than at runtime.
For early binding to take place, an object variable must be declared as a specific
object type (that is, not As Object). Change the Dim statement in the code you’ve
entered to read as follows:
Dim objMyObject As clsMyClass
As soon as you commit this statement, Visual Basic displays a wavy blue line under
the bad method call, as shown in Figure 16.6. This occurs because Visual Basic now
knows the exact type of object the variable will contain; therefore, it can and does
perform syntax checking on all member references. Because it can’t find a member
with the name AddtoNumbers, it flags this as a build error. Try running the project by
pressing F5, and you’ll see that Visual Basic does indeed recognize this as a build
problem.
Place the cursor at the period between the words objMyObject and AddtoNumbers.
Delete the period and then type a period once more. This time, Visual Basic displays
an IntelliSense drop-down list with all the members of the class, as shown in Figure
16.7. Go ahead and select the AddTwoNumbers member to fix your code.
Creating a New Object When Dimensioning a Variable
You can instantiate a new object on the declaration statement by including the keyword
New, like this:
Instantiating Objects from Classes 361
FIGURE 16.6
With early-bound
objects, Visual
Basic performs
syntax checking
for you.
FIGURE 16.7
Visual Basic displays
IntelliSense
drop-down lists
of members for
early-bound
objects.
Dim objMyObject As New clsMyClass()
This approach alleviates the need for a second statement to create a new instance of
the object. However, if you do this, the variable will always contain a reference to an
362 HOUR 16: Designing Objects Using Classes
object. If there’s a chance that you might not need the object, you should probably
avoid using the New keyword on the Dim statement. Consider the following:
Dim objMyObject As clsMyClass
If condition Then
objMyObject = New clsMyObject
‘ Code to use the custom object would go here.
End If
Remember that instantiating an object takes resources. In this code, no object is created
when condition is False. If you were to place the word New on the Dim statement,
a new object would be instantiated whenever this code was executed,
regardless of the value of condition.
Releasing Object References
When an object is no longer needed, it should be destroyed so that all the resources
used by the object can be reclaimed. Objects are destroyed automatically when the
last reference to the object is released. Although there are two primary ways to
release an object reference, one is clearly better than the other.
One way to release a reference to an object is simply to let the object variable holding
the reference go out of scope. As you might recall from Hour 11, variables are
destroyed when they go out of scope. This is no less true for object variables. However,
you can’t necessarily be assured that an object is fully released and that all the
memory being used by the object is freed by letting the object’s variable go out of
scope. Therefore, relying on scope to release objects isn’t a good idea.
To explicitly release an object, set the object variable equal to Nothing, like this:
objMyObject = Nothing
When you set an object variable equal to Nothing, you’re assured that the object reference
is fully released. The object won’t be destroyed, however, if other variables are
referencing it. After the last reference is released, the garbage collector eventually
destroys the object. (I talk about the garbage collector in Hour 24, “The 10,000-Foot
View.”) Go ahead and add the statement just shown to your procedure, right after the
statement that shows the message box.
If you don’t correctly release object references, your application might experience
resource leaks, become sluggish, and consume more resources than it should.
Understanding the Lifetime of an Object
An object created from a class exists as long as a variable holds a reference to it. Fortunately,
Visual Basic (or, more specifically, the .NET Framework, as discussed in
Summary 363
Hour 24) handles the details of keeping track of the references to a given object; you
don’t have to worry about this when creating or using objects. When all the references
to an object are released, the object is flagged and eventually destroyed by the
garbage collector.
The following are key points to remember about an object’s lifetime and what they
mean to your application:
. An object is created (and hence referenced) when an object variable is declared
by the keyword New. For example:
Dim objMyObject = New clsMyClass()
. An object is created (and hence referenced) when an object variable is assigned
an object by the keyword New. For example:
objMyObject = New clsMyClass()
. An object is referenced when an object variable is assigned an existing object.
For example:
objThisObject = objThatObject
. An object reference is released when an object variable is set to Nothing, as discussed
in the preceding section.
. An object is destroyed sometime after the last reference to it is released. This is
handled by the garbage collector, as discussed in Hour 24.
Understanding the lifetime of objects is important. You’ve now seen how and when
object references are created, but you also need to know how to explicitly release an
object reference. Only when all references to an object are released is the object
flagged for destruction and the resources it uses are reclaimed.
Summary
Object-oriented programming is an advanced methodology that enables you to create
more robust applications, and programming classes is the foundation of OOP. In
this hour, you learned how to create classes, which are the templates used to instantiate
objects. You also learned how to create a custom interface consisting of properties
and methods, and how to use the classes you’ve defined to instantiate and manipulate
objects by way of object variables.
Visual Basic is on par with languages such as C++ for OOP capabilities. In this hour,
you learned the basic mechanics of programming objects with classes. Objectoriented
programming takes considerable skill, and you’ll need to master the concepts
in this book before you can really begin to take advantage of what OOP has
364 HOUR 16: Designing Objects Using Classes
to offer. Nevertheless, what you learned in this hour will take you further than you
might think. Using an OOP methodology is as much a way of thinking as it is a way
of programming. Consider how things in your projects might work as objects, and
before you know it, you’ll be creating robust classes.
Q&A
Q. Should I always try to place code in classes rather than standard modules?
A. Not necessarily. As with most things, there are no hard-and-fast rules. Correctly
programming classes takes some skill and experience, and programming standard
modules is easier for beginners. If you want to experiment with classes, I
encourage you to do so. However, don’t feel as though you have to place everything
in a class.
Q. I want to create a general class with many miscellaneous procedures—sort
of a catchall class. What’s the best way to do this?
A. If you want to create some sort of utility class, I recommend calling it something
like clsUtility. Create a global variable to hold a reference to an object
instantiated from this class. In your program’s startup code, set the global variable
to a new instance of the class. Then you can use the global variable
throughout your application to access the utility functions instead of having to
instantiate a new object each time you want to use the functions.
Workshop
Quiz
1. To create objects, you must first create a template. What is this template
called?
2. One of the primary benefits of object-oriented programming is that objects
contain both their data and their code. What is this capability called?
3. With standard modules, public variables and routines are always available to
code in other modules. Is this true with public variables and routines in
classes?
4. True or false: Each object derived from a class has its own set of module-level
data.
Workshop 365
5. What must you do to create a property that can be read but not changed by
client code?
6. What’s the best way to store the internal value of a property within a class?
7. Which is generally superior, early binding or late binding?
8. If an object variable is declared As Object, is it early-bound or late-bound?
9. What’s the best way to destroy an object reference?
Answers
1. Class
2. Encapsulation
3. No. An object would have to be instantiated before the public variables and
routines would be available.
4. True
5. Declare the property procedure by using the ReadOnly modifier, and remove
the Set...End Set section.
6. Store the internal value in a private module-level variable.
7. Early binding is almost always superior to late binding.
8. The object is late-bound.
9. Set the object variable equal to Nothing.
Exercises
1. Add a new property to your class called DropsInABucket. Make this property a
Long, and set it up so that client code can read the property value but not set it.
Finally, add a button to the form that, when clicked, prints the value of the
property to the Immediate window (it will be 0 by default). When this is working,
modify the code so that the property always returns 1,000,000.
2. Add a button to your form that creates two object variables of type
clsMyClass(). Use the New keyword to instantiate a new instance of the class
in one of the variables. Then set the second variable to reference the same
object and print the contents of the Height property to the Output window or
display it in a message box.
This page intentionally left blank
Displaying Messages Using the MessageBox.Show() Function 367
HOUR 17
Interacting with Users
What You’ll Learn in This Hour:
. Displaying messages using the MessageBox.Show() function
. Creating custom dialog boxes
. Using InputBox() to get information from a user
. Interacting with the keyboard
. Using the common mouse events
Forms and controls are the primary means by which users interact with an application,
and vice versa. However, program interaction can and often does go deeper
than that. For example, a program can display customized messages to a user, and it
can be fine-tuned to deal with certain keystrokes or mouse clicks. In this hour, you’ll
learn how to create functional and cohesive interaction between your application
and the user. In addition, you’ll learn how to program the keyboard and mouse so
that you can expand your program’s interactivity beyond what a form and its controls
natively support.
Displaying Messages Using the
MessageBox.Show() Function
A message box is a small dialog box that displays a message to the user (just in case
that’s not obvious). Message boxes are often used to tell the user the result of some
action, such as “The file has been copied” or “The file could not be found.” A message
box is dismissed when the user clicks one of its available buttons. Most applications
have many message boxes, but developers often don’t display messages
correctly. It’s important to remember that when you display a message to a user,
you’re communicating with the user. In this section, I’ll teach you not only how to
use the MessageBox.Show() function to display messages, but also how to use the
statement to communicate effectively.
368 HOUR 17: Interacting with Users
The MessageBox.Show() function can be used to tell the user something or ask the
user a question. In addition to displaying text, which is its primary purpose, you can
use this function to display an icon and display one or more buttons that the user
can click. Although you’re free to display whatever text you want, you must choose
from a predefined list of icons and buttons.
The MessageBox.Show() method is an overloaded method. This means that it was
written with numerous constructs supporting various options. When you code in
Visual Basic, IntelliSense displays a drop-down scrolling list displaying any of the 21
overloaded MessageBox.Show() method calls to aid in coding. The following are a
few ways to call MessageBox.Show():
To display a message box with specified text, a caption in the title bar, and an OK
button, use this syntax:
MessageBox.Show(MessageText, Caption)
To display a message box with specified text, a caption, and one or more specific buttons,
use this syntax:
MessageBox.Show(MessageText, Caption, Buttons)
To display a message box with specified text, a caption, buttons, and an icon, use
this syntax:
MessageBox.Show(MessageText, Caption, Buttons, Icon)
In all these statements, MessageText is the text to display in the message box,
Caption determines what appears in the message box’s title bar, Buttons determines
which buttons the user sees, and Icon determines what icon (if any) appears in the
message box. Consider the following statement, which produces the message box
shown in Figure 17.1:
MessageBox.Show(“This is a message.”, “Hello There”)
You should always ensure that the buttons displayed are appropriate for the message.
As you can see, if you omit Buttons, Visual Basic displays only an OK button.
FIGURE 17.1
A simple message
box.
Displaying Messages Using the MessageBox.Show() Function 369
By the
Way The older-style basic MsgBox() function (which is still supported, although not
recommended) defaults the caption for the message box to the name of the project.
There is no default for MessageBox.Show(), so you should always specify a
caption, or you’ll get an empty title bar for the dialog box.
Specifying Buttons and an Icon
Using the Buttons parameter, you can display one or more buttons in the message
box. The Buttons parameter type is MessageBoxButtons. Table 17.1 shows the allowable
values.
Because the Buttons parameter is an enumerated type, Visual Basic gives you an
IntelliSense drop-down list when you specify a value for this parameter. Therefore,
committing these values to memory isn’t all that important; you’ll commit to memory
the ones you use most often fairly quickly.
The Icon parameter determines the symbol displayed in the message box. The Icon
parameter is an enumeration from the MessageBoxIcon type. Table 17.2 shows the
most commonly used values of MessageBoxIcon.
TABLE 17.1 Allowable Enumerators for MessageBoxButtons
Member Description
AbortRetryIgnore Displays Abort, Retry, and Ignore buttons.
OK Displays an OK button only.
OKCancel Displays OK and Cancel buttons.
YesNoCancel Displays Yes, No, and Cancel buttons.
YesNo Displays Yes and No buttons.
RetryCancel Displays Retry and Cancel buttons.
TABLE 17.2 Common Enumerators for MessageBoxIcon
Member Description
Exclamation Displays a symbol consisting of an exclamation point in a
triangle with a yellow background.
Information Displays a symbol consisting of a lowercase letter i in a
circle.
None Displays no symbol.
Question Displays a symbol consisting of a question mark in a
circle.
370 HOUR 17: Interacting with Users
The Icon parameter is also an enumerated type; therefore, Visual Basic gives you an
IntelliSense drop-down list when you specify a value for this parameter. You may have
noticed that Exclamation and Warning have the same icon. As best I can tell, this is a
throwback to early versions of Visual Basic, and either work just fine. Whichever you
choose, I suggest you pick one and stick with it for the sake of consistency.
The message box shown in Figure 17.2 was created with the following statement:
MessageBox.Show(“I’m about to do something...”,”MessageBox sample”, _
MessageBoxButtons.OKCancel,MessageBoxIcon.Information)
The message box shown in Figure 17.3 was created with a statement almost identical
to the previous one, except that the second button is designated as the default button.
If a user presses the Enter key with a message box displayed, the message box acts as
though the user clicked the default button. You’ll want to give careful consideration
to the default button in each message box. For example, suppose the application is
about to do something that the user probably doesn’t want to do. It’s best to make the
Cancel button the default button in case the user is a bit quick when pressing the
Enter key. Following is the statement used to generate the message box shown in
Figure 17.3:
MessageBox.Show(“I’m about to do something irreversible...”, _
“MessageBox sample”, _
MessageBoxButtons.OKCancel,MessageBoxIcon.Information, _
MessageBoxDefaultButton.Button2)
FIGURE 17.2
Assign the Information
icon to
general messages.
TABLE 17.2 Continued
Member Description
Stop Displays a symbol consisting of a white X in a circle with
a red background.
Warning Displays a symbol consisting of an exclamation point in a
triangle with a yellow background.
FIGURE 17.3
The default button
has a dark
border.
Displaying Messages Using the MessageBox.Show() Function 371
The Error icon is shown in Figure 17.4. The Error icon is best used in rare circumstances,
such as when an exception has occurred. Overusing the Error icon is like crying
wolf—when a real problem emerges, the user might not notice. Notice here how I
display only the OK button. If something has already happened and there’s nothing
the user can do about it, don’t bother giving the user a Cancel button. The following
statement generates the message box shown in Figure 17.4:
MessageBox.Show(“Something bad has happened!”,”MessageBox sample”, _
MessageBoxButtons.OK, MessageBoxIcon.Error)
In Figure 17.5, a question is posed to the user, so the message displays the Question
icon. Also note how the message box assumes that the user would probably choose
No, so the second button is set as the default. In the next section, you’ll learn how to
determine which button the user clicks. Here’s the statement used to generate the
message box shown in Figure 17.5:
MessageBox.Show(“Would you like to format your hard drive now?”, _
“MessageBox sample”,MessageBoxButtons.YesNo,MessageBoxIcon.Question, _
MessageBoxDefaultButton.Button2)
As you can see, designating buttons and icons isn’t all that difficult. The real effort
comes in determining which buttons and icons are appropriate for a given situation.
FIGURE 17.4
If users have no
control over what
has occurred,
don’t give them
a Cancel button.
FIGURE 17.5
A message box
can be used to
ask a question.
372 HOUR 17: Interacting with Users
By the
Way
TABLE 17.3 Enumerators for DialogResult
Member Description
Abort The return value is Abort. Usually sent from a button labeled Abort.
Cancel The return value is Cancel. Usually sent from a button labeled
Cancel.
Ignore The return value is Ignore. Usually sent from a button labeled Ignore.
No The return value is No. Usually sent from a button labeled No.
None Nothing is returned from the dialog box. The model dialog continues
running.
OK The return value is OK. Usually sent from a button labeled OK.
Retry The return value is Retry. Usually sent from a button labeled Retry.
Yes The return value is Yes. Usually sent from a button labeled Yes.
Determining Which Button Is Clicked
You’ll probably find that many of your message boxes are simple, containing only an
OK button. For other message boxes, however, you must determine which button a
user clicks. Why give the user a choice if you won’t act on it?
The MessageBox.Show() method returns the button clicked as a DialogResult enumeration.
The DialogResult has the values shown in Table 17.3.
Note the phrase “Usually sent from” in the descriptions of the DialogResult values.
When you create custom dialog boxes (as shown later in this hour), you can
assign a DialogResult to any button of your choosing.
Performing actions based on the button clicked is a matter of using one of the decision
constructs. For example:
If (MessageBox.Show(“Would you like to do X?”,”MessageBox sample”, _
MessageBoxButtons.YesNo,MessageBoxIcon.Question) = _
Windows.Forms.DialogResult.Yes) Then
‘ Code to do X would go here.
End If
As you can see, the MessageBox.Show()method gives you a lot of bang for your
buck; it offers considerable flexibility.
Creating Custom Dialog Boxes 373
Creating Good Messages
The MessageBox.Show() method is surprisingly simple to use, considering all the different
forms of messages it lets you create. The real trick is providing appropriate messages
to users at appropriate times. In addition to considering the icon and buttons to
display in a message, you should follow these guidelines for crafting message text:
. Use a formal tone. Don’t use large words, and avoid using contractions.
Strive to make the text immediately understandable and not overly fancy; a
message box is not a place to show off your literary skills.
. Limit messages to two or three lines. Not only are lengthy messages more
difficult for users to read, but they also can be intimidating. When a message
box is used to ask a question, make the question as succinct as possible.
. Never make users feel as though they’ve done something wrong. Users
will, and do, make mistakes, but you should craft messages that take the sting
out of the situation.
. Spell-check all message text. The Visual Basic code editor doesn’t spellcheck
for you, so you should type your messages in a program such as
Microsoft Word and spell-check the text before pasting it into your code.
Spelling errors have an adverse effect on a user’s perception of a program.
. Avoid technical jargon. Just because someone uses software doesn’t mean
that he is a technical person. Explain things in plain English (or whatever the
native language of the GUI happens to be).
. Be sure that the buttons match the text! For example, don’t show the
Yes/No buttons if the text doesn’t present a question to the user.
Creating Custom Dialog Boxes
Most of the time, the MessageBox.Show() method should be a sufficient means to
display messages to a user. At times, however, the MessageBox.Show() method is too
limited for a given purpose. Suppose that you want to display a lot of text to the user,
such as a log file of some sort, for example, so you want a message box that the user
can size.
Custom dialog boxes are nothing more than standard modal forms, with one notable
exception: One or more buttons are designated to return a dialog result, just as the
buttons on a message box shown with the MessageBox.Show() method return a dialog
result.
374 HOUR 17: Interacting with Users
Property Value
Name btnShowCustomDialogBox
Location 67, 180
Size 152, 23
Text Show Custom Dialog Box
Property Value
Name txtCustomMessage
Location 8, 8
Multiline True
ReadOnly True
Size 268, 220
Text Custom message goes here
Property Value
Name btnCancel
DialogResult Cancel
Location 201, 234
Now you’ll create a custom dialog box. Begin by creating a new Windows Application
titled Custom Dialog Example, and then follow these steps to build the project:
1. Rename the default form MainForm.vb, and set its Text property to Custom
Dialog Box Example.
2. Add a new button to the form, and set its properties as follows:
3. Now you’ll create the custom dialog box. Add a new form to the project by
choosing Project, Add Windows Form. Save the new form with the name
CustomDialogBoxForm.vb.
4. Change the Text property of the new form to This is a custom dialog box,
and set its FormBorderStyle to FixedDialog.
5. Add a new text box to the form, and set its properties as follows:
For a custom dialog box to return a result as a standard message box does, it
must have buttons that are designated to return a dialog result. You do this by
setting a button’s DialogResult property, as shown in Figure 17.6.
6. Add a new button to the form, and set its properties as shown in the following
table. This button will act as the custom dialog box’s Cancel button.
Creating Custom Dialog Boxes 375
FIGURE 17.6
The
DialogResult
property determines
the button’s
return
value.
Property Value
Name btnOK
DialogResult OK
Location 120, 234
Size 75, 23
Text OK
Size 75, 23
Text Cancel
7. You need to create an OK button for the custom dialog box. Create another button
and set its properties as follows:
Specifying a dialog result for one or more buttons is the first step in making a
form a custom dialog box. The second part of the process is in how the form is
shown. As you learned in Hour 5, “Building Forms: The Basics,” you display
forms by calling the Show() method of a form variable. However, to show a
form as a custom dialog box, you call the ShowDialog() method instead.
When ShowDialog() is used to display a form, the following occurs:
. The form is shown modally.
. If the user clicks a button that has its DialogResult property set to return a
value, the form is immediately closed, and that value is returned as a result of
the ShowDialog() method call.
Notice how you don’t have to write code to close the form; clicking a button
with a dialog result closes the form automatically. This simplifies the process of
creating custom dialog boxes.
376 HOUR 17: Interacting with Users
By the
Way
FIGURE 17.7
The
ShowDialog()
method enables
you to create
custom message
boxes.
8. Return to the first form in the Form Designer by double-clicking MainForm.vb
in the Solution Explorer.
9. Double-click the button you created, and add the following code:
If CustomDialogBoxForm.ShowDialog() = Windows.Forms.DialogResult.OK Then
MessageBox.Show(“You clicked OK.”)
Else
MessageBox.Show(“You clicked Cancel.”)
End If
When you typed the equals sign after ShowDialog(), did you notice that Visual Basic
gave you an IntelliSense drop-down list with the possible dialog results? These results
correspond directly to the values you can assign to a button when you use the
DialogResult property. Press F5 to run the project, click the button to display your
custom dialog box (see Figure 17.7), and then click one of the available dialog box
buttons. When you’re satisfied that the project is working correctly, stop the project
and save your work.
If you click the Close (X) button in the upper-right corner of the form, the form is
closed, and the code behaves as if you’ve clicked Cancel because the Else code
occurs.
The ability to create custom dialog boxes is a powerful feature. A call to
MessageBox.Show() is usually sufficient, but when you need more control over the
appearance and contents of a message box, creating a custom dialog box is the
way to go.
Using InputBox() to Get Information from a User 377
FIGURE 17.8
The input box
enables a user
to enter a single
piece of information.
Using InputBox() to Get Information
from a User
The MessageBox.Show() method enables you to ask the user simple Yes/No, OK/
Cancel–type questions, but it doesn’t let you get specific input from a user, such as
text or a number. When you need input from a user, you have two choices:
. Create a form with one or more controls to capture the data.
. Use the InputBox() function to gather data from the user.
The InputBox() function can capture only one piece of data, so it’s not appropriate
for most data-entry situations. However, in some circumstances, you might find that
you need only one piece of data, and creating a custom form in such a situation
would be overkill. For example, suppose that you have a simple application and you
want the user to enter a name when he or she first starts the application. You could
use the InputBox() function to have the user enter his or her name, rather than
designing a special form.
The basic syntax of the InputBox() function looks like this:
InputBox(prompt, [title], [defaultresponse])
The first two parameters are similar to the corresponding parameters in
MessageBox.Show(). The first parameter is the prompt to display to the user. This is
where you specify the instructions or question that you want posed to the user. The
title parameter determines the text that appears in the title bar. Again, if you omit
title, the name of the project is shown. The following statement creates the input
box shown in Figure 17.8:
strResult = InputBox(“What is your favorite color?”, “Enter Color”)
378 HOUR 17: Interacting with Users
FIGURE 17.9
You can specify
a default value
for the user.
Property Value
Name btnGetAge
Location 105, 109
Size 75, 23
Text Enter Age
The last parameter, defaultresponse, enables you to specify text that appears by
default in the text box portion of the input box. For example, the following statement
produces the input box shown in Figure 17.9:
strResult = InputBox(“How many eggs do you want to order?”, “Order Eggs”, “12”)
3. Double-click the button to access its Click event, and enter the following code:
Dim strResult As String
Dim intAge As Integer
strResult = InputBox(“Please enter your age.”, “Enter Age”)
If strResult = ““ Then
MessageBox.Show(“You clicked cancel!”)
ElseIf IsNumeric(strResult) Then
‘ The user entered a number, store the age as a number.
intAge = CInt(strResult)
MessageBox.Show(“You entered “ & intAge & “.”)
Else
MessageBox.Show(“You did not enter a number.”)
End If
You should keep in mind two things about the return value of InputBox(). The first
is that the result is always a string. The second is that an empty string is returned if
the user clicks Cancel. The fact that InputBox() can return only a string and not a
number data type is a limitation, but it’s one that you can work around.
Now you’ll create a project that uses an InputBox() to get the user’s age. If the user
clicks Cancel or enters something other than a number, the program behaves accordingly.
Begin by creating a new Windows Application titled InputBox Example, and
then follow these steps to build the project:
1. Rename the default form MainForm.vb, and then set its Text property to
InputBox Example.
2. Add a new button to the form, and set its properties as follows:
Interacting with the Keyboard 379
By the
Way
TABLE 17.4 Events That Handle Keyboard Input
Event Name Description
KeyDown Occurs when a key is pressed while the control has the focus.
KeyPress Occurs when a key is pressed while the control has the focus. If
the user holds down the key, this event fires multiple times.
KeyUp Occurs when a key is released while the control has the focus.
Nothing in this procedure, short of the call to InputBox(), should be new to you.
What happens here is that the InputBox() function is used to ask the user to enter
his or her age. Because InputBox() always returns a string, you use a string variable
to hold the result. Next, an If...Else If...Else...End If construct is used to
evaluate the result of the InputBox() call. The first test looks to see whether the result
is a zero-length string. If it is, the code assumes that the user clicked Cancel. Next, the
result is evaluated to see whether it is a number. If it is a number, the result is converted
to an integer and displayed to the user. Go ahead and Press F5 and test the
project.
If the user doesn’t enter anything, an empty string is returned, just as though he
or she clicked Cancel. There’s no way to know the difference between clicking
Cancel and not entering any text when using InputBox().
InputBox() is a useful function for gathering a single piece of information. As you
can see, it’s possible to work around the limitation of the function’s returning only a
string. Keep the InputBox() function in mind; at times, it will come in handy.
Interacting with the Keyboard
Although most every control on a form handles its own keyboard input, on occasion
you’ll want to handle keyboard input directly. For example, you might want to perform
an action when the user presses a specific key or releases a specific key. Most
controls support three events that you can use to work directly with keyboard input.
These are listed in Table 17.4.
These events fire in the same order in which they appear in Table 17.4. For example,
suppose that the user presses a key while a text box has the focus. The following list
shows how the events would fire for the text box:
1. When the user presses a key, the KeyDown event fires.
2. While the key is down, the KeyPress event fires. This event repeats as long as
the key is held down.
380 HOUR 17: Interacting with Users
Property Value
Name txtInput
Location 23, 56
Multiline True
Size 238, 120
3. When the user releases the key, the KeyUp event fires, completing the cycle of
keystroke events.
If you were creating a text editor and needed to perform an action for every keystroke
entered by a user, for example, you would need to use the KeyPress event. This is the
only event that would work because when a user holds down a key, Windows repeats
the key in a text box or other data entry control. The KeyPress event fires for each repetition
of the key, whereas KeyDown and KeyUp fire only once for each physical press
of a key, regardless of how long the key is held down.
Now you’ll create a project that illustrates handling keystrokes. This project has a text
box that refuses to accept any character that isn’t a number. Basically, you’ll create a
numeric text box. Start by creating a new Windows Application titled Keyboard
Example, and then follow these steps to build the project:
1. Right-click Form1.vb in the Solution Explorer, choose Rename, change the
name of the default form to KeyboardExampleForm.vb, and set its Text property
to Keyboard Example.
2. Add a new text box to the form, and set its properties as shown in the following
table:
3. You’ll add code to the KeyPress event of the text box to “eat” keystrokes that
aren’t numbers. Double-click the text box now to access its default event.
4. We’re not interested in the TextChanged event, so choose KeyPress from the
event list in the upper right of the code window.
5. Go ahead and delete the TextChanged event because you won’t be using it.
Your code editor should now look like Figure 17.10.
As you learned in Hour 4, “Understanding Events,” the e parameter contains information
specific to the occurrence of this event. In keyboard-related events, the e
parameter contains information about the key being pressed; it’s what you’ll use to
work with the user’s keystrokes.
Interacting with the Keyboard 381
FIGURE 17.10
The KeyPress
event is a good
place to handle
keyboard entry.
The key being pressed is available as the KeyChar property of the e parameter. You’ll
write code that handles the keystroke when the pressed key is anything other than a
number.
Add the following code to the KeyPress event:
If Not (IsNumeric(e.KeyChar)) Then
e.Handled = True
End If
You’re probably curious about the Handled property of the e object. When you set this
property to True, you’re telling Visual Basic that you handled the keystroke and that
Visual Basic should ignore it (that is, not add it to the text box). To see the effect this
has, press F5 to run the project, and enter text into the text box. Try entering both
numbers and letters; you’ll find that only the numbers appear in the text box (see
Figure 17.11).
When you paste data from the Clipboard, the KeyPress event isn’t fired for each keystroke.
Therefore, it’s possible that a nonnumeric character could appear in the text
box. If you absolutely needed to keep nonnumeric characters out of the text box,
you’d need to use the TextChanged event as well.
382 HOUR 17: Interacting with Users
FIGURE 17.11
The keyboard
events enable
you to handle
keystrokes as
you see fit.
TABLE 17.5 Events That Handle Mouse Input
Event Name Description
MouseEnter Occurs when the pointer enters a control.
MouseMove Occurs when the pointer moves over a control.
MouseHover Occurs when the pointer hovers over a control.
MouseDown Occurs when the pointer is over a control and a button is pressed.
MouseUp Occurs when the pointer is over a control and a button is released.
MouseLeave Occurs when the pointer leaves a control.
Click Occurs between the MouseDown and MouseUp events.
Using the Common Mouse Events
As with keyboard input, most controls support mouse input natively; you don’t have
to write code to deal with mouse input. At times, you might need more control than
that offered by a control’s native functionality, however. Visual Basic supports seven
events that enable you to deal with mouse input directly. These events are listed in
Table 17.5 in the order in which they occur.
It’s not often that I need to catch a keypress, but every now and then I do. The
three keystroke events listed in Table 17.4 have always made it easy to do what I
need to do, but if there’s one caveat I’ve discovered, it’s that you need to give
careful consideration to which event you choose (such as KeyPress or KeyUp, for
example). Different events work best in different situations, and the best thing to
do is to start with what seems like the most logical event, test the code, and
change the event if necessary.
By the
Way
Using the Common Mouse Events 383
Now you’ll build a project that illustrates using the MouseMove event to interact with
the mouse. This project enables a user to draw on a form, much like you can draw in
a paint program. Begin by creating a new Windows Application titled Mouse Paint,
and then follow these steps to create the project:
1. Right-click Form1.vb in the Solution Explorer and choose Rename. Then
change the name of the default form to MainForm.vb and set its Text property
to Paint with the Mouse.
2. Double-click the form to access its default event, the Load event. Enter the following
statement into the Load event:
m_objGraphics = Me.CreateGraphics
You’ve already used a graphics object a few times. What you’re doing here is
setting a graphics object to the client area of the form; any drawing performed
on the object appears on the form. Because you’ll draw to this graphics object
each time the mouse moves over the form, there’s no point in creating a new
graphics object each time you need to draw to it. Therefore, you’ll make
m_objGraphics a module-level variable, which is instantiated only once—in
the form’s Load event.
3. Enter this statement into the Declarations section of your form class (between
the Public Class MainForm statement and the Private Sub statement for
your event procedure):
Private m_objGraphics As Graphics
As mentioned previously, always destroy objects when you’re done with them.
In this case, you want the object to remain in existence for the life of the form.
Therefore, you’ll destroy it in the form’s FormClosed event, which occurs when
the form is unloaded.
4. Open the object drop-down list (the upper-left drop-down list) and choose
(MainForm Events). Next, open the procedure drop-down list (the drop-down list
in the upper right), and select FormClosed. Enter the following statement in
the FormClosed event:
m_objGraphics.Dispose()
Your procedure should now look like the one shown in Figure 17.12.
The last bit of code you need to add is the code that will draw on the form.
You’ll place code in the form’s MouseMove event to do this. First, the code makes
sure that the left mouse button is held down. If it isn’t, no drawing takes place;
384 HOUR 17: Interacting with Users
FIGURE 17.12
Code in many
places often
works together
to achieve one
goal.
the user must hold down the mouse button to draw. Next, a rectangle is created.
The coordinates of the mouse pointer are used to create a small rectangle
that is passed to the DrawEllipse method of the graphics object. This has the
effect of drawing a tiny circle where the mouse pointer is positioned.
5. Again, select (MainForm Events) from the object drop-down list, and this time
select MouseMove from the list of event procedures. Add the following code to
the MouseMove event:
Dim rectEllipse As Rectangle
If e.Button <> Windows.Forms.MouseButtons.Left Then Exit Sub
With rectEllipse
.X = e.X - 1
.Y = e.Y - 1
.Width = 2
.Height = 2
End With
m_objGraphics.DrawEllipse(System.Drawing.Pens.Blue, rectEllipse)
Like all events, the e object contains information related to the event. In this example,
you’re using the X and Y properties of the e object, which are the coordinates of
the pointer when the event fires. In addition, you’re checking the Button property of
the object to make sure that the user is pressing the left button.
Summary 385
FIGURE 17.13
Capturing mouse
events opens
many exciting
possibilities.
Your project is now complete! Save your work by clicking Save All on the toolbar, and
then press F5 to run the project. Move the mouse over the form—nothing happens.
Now, hold down the left mouse button and move the mouse. This time, you draw on
the form, as shown in Figure 17.13.
Notice that the faster you move the mouse, the more space appears between circles.
This shows you that the user can move the mouse faster than the MouseMove event
can fire, so you can’t catch every single movement of the mouse. This is important to
remember.
Summary
Forms and controls allow a lot of flexibility in how a user interacts with an application.
However, solid interactivity goes beyond just what is placed on a form. In this
hour, you learned how to use the MessageBox.Show() function to create informational
dialog boxes. You learned how to specify an icon and buttons, and even how
to designate a specific button as the default button. You also learned some valuable
tips to help create the best messages possible. You’ll create message boxes frequently,
so mastering this skill is important.
Sometimes a simple OK/Cancel or Yes/No question isn’t applicable—you need more
data from the user. In this hour, you learned how to use the InputBox() function to
get a single piece of data from the user and how to create custom dialog boxes.
Although InputBox() always returns a string, you learned how to use it to gather
numeric input as well.
Finally, you learned how to interact with the keyboard and mouse directly through
numerous events. A control’s mouse or keyboard capabilities sometimes fall short of
what you want to accomplish. By understanding the concepts presented in this hour,
386 HOUR 17: Interacting with Users
you can go beyond the native capabilities of controls to create a rich, interactive
experience for your users.
Q&A
Q. Is it possible to capture keystrokes at the form level, rather than capturing
them in control events?
A. Yes. For the form’s keyboard-related events to fire when a control has the focus,
however, you must set the form’s KeyPreview property to True. The control’s
keyboard events still fire, unless you set KeyPressEventArgs.Handled to True
in the control’s KeyPress event.
Q. If I need to gather two or three pieces of information from the user, is it okay
to use multiple InputBox statements?
A. Probably not. In this case, a form or custom dialog box is probably a better
choice.
Workshop
Quiz
1. What argument must you always supply a value for when calling
MessageBox.Show()?
2. If you don’t supply a value for the Caption parameter of MessageBox.Show(),
what is displayed in the title bar of the message box?
3. How many icons can you show in a message box at once?
4. What type of data does the InputBox() function always return?
5. What does InputBox() return when the user clicks Cancel?
6. Which event fires first, KeyUp or KeyPress?
7. How do you determine which button is being pressed in a mouse-related event?
Workshop 387
Answers
1. The prompt and the dialog title (caption). Actually, technically the caption is
optional, but it’s such a bad idea to leave it off that I consider it required.
2. Nothing gets displayed—the title bar is empty.
3. Only one icon can be shown at a time.
4. The InputBox() function always returns a string.
5. An empty string is returned when the user clicks Cancel.
6. The KeyPress event fires before the KeyUp event.
7. By using the e.Button property in the event.
Exercises
1. Modify your custom dialog box project so that the OK button is the form’s
Accept button. That way, the user must only press Enter to dismiss the dialog
box. Next, make the Cancel button the form’s Cancel button so that the user
can also press the Escape key to dismiss the form.
2. Modify your mouse paint project so that the form clears each time the user
starts drawing. Hint: Clear the graphics object in the MouseDown event to the
form’s BackColor.
This page intentionally left blank
Understanding the Graphics Object 389
HOUR 18
Working with Graphics
What You’ll Learn in This Hour:
. Understanding the Graphics object
. Working with pens
. Using system colors
. Working with rectangles
. Drawing shapes
. Drawing text
. Persisting graphics on a form
. Building a graphics project example
Visual Basic provides an amazingly powerful array of drawing capabilities. However,
this power comes at the price of a relatively steep learning curve. Drawing isn’t intuitive;
you can’t sit down for a few minutes with the online Help text and start drawing
graphics. However, after you learn the basic principles involved, you’ll find that
drawing isn’t that complicated. In this hour, you’ll learn the basic skills for drawing
shapes and text to a form or other graphical surface. You’ll learn about pens, colors,
and brushes (objects that help define graphics that you draw). In addition, you’ll
learn how to persist graphics on a form—and even how to create bitmaps that exist
solely in memory.
Understanding the Graphics Object
At first, you might not come up with many reasons to draw to the screen, preferring
to use the many advanced controls found within Visual Basic to build your interfaces.
However, as your applications increase in size and complexity, you’ll find more
and more occasions to draw your own interfaces directly to the screen; when you
need this functionality, you really need this functionality. You might even choose to
390 HOUR 18: Working with Graphics
design your own controls (which you can do with Visual Basic). In this hour, you’ll
learn the basics of drawing and printing to the screen. Using the skills you’ll acquire
in this hour, you’ll be able to build incredibly detailed interfaces that look exactly
how you want them to look.
The code within the Windows operating system that handles drawing everything to
the screen, including text, lines, and shapes, is called the Graphical Device Interface
(GDI). The GDI processes all drawing instructions from applications, as well as from
Windows itself, and generates the output for the current display. Because the GDI
generates what you see onscreen, it is responsible for dealing with the particular display
driver installed on the computer and the driver’s settings, such as resolution and
color depth. This means that applications (and their developers) don’t have to worry
about these details; you write code that tells the GDI what to output, and the GDI
does whatever is necessary to produce that output. This behavior is called device independence
because applications can instruct the GDI to display text and graphics,
using code that’s independent of the particular display device.
Visual Basic code communicates with the GDI primarily via the Graphics object. The
basic process is as follows:
. An object variable is created to hold a reference to a Graphics object.
. The object variable is set to a valid Graphics object (new or existing).
. To draw or print, you call methods of the Graphics object.
Creating a Graphics Object for a Form or Control
If you want to draw directly to a form or control, you can easily get a reference to the
drawing surface by calling the CreateGraphics() method of the object in question.
For example, to create a Graphics object that draws to a text box, you could use
code such as this:
Dim objGraphics As Graphics = TextBox1.CreateGraphics
When you call CreateGraphics(), you’re setting the object variable to hold a reference
to the Graphics object of the form or control’s client area. The client area of a
form is the gray area within the form’s borders and title bar, whereas the client area
of a control is usually the entire control. All drawing and printing done using the
Graphics object are sent to the client area. In the code shown previously, the
Graphics object references the client area of a text box, so all drawing methods executed
on the Graphics object would draw directly to the text box.
Understanding the Graphics Object 391
By the
Way
TABLE 18.1 Common Values for pixelformat
Value Description
Format16bppGrayScale The pixel format is 16 bits per pixel. The color
information specifies 65,536 shades of gray.
Format16bppRgb555 The pixel format is 16 bits per pixel. The color
information specifies 32,768 shades of color, of which
5 bits are red, 5 bits are green, and 5 bits are blue.
Format24bppRgb The pixel format is 24 bits per pixel. The color
information specifies 16,777,216 shades of color, of
which 8 bits are red, 8 bits are green, and 8 bits are
blue.
When you draw directly to a form or control, the object in question doesn’t persist
what’s drawn on it. If the form is obscured in any way, such as by a window covering
it or the form’s being minimized, the next time the form is painted, it won’t
contain anything that was drawn on it. Later in this hour, I’ll teach you how to persist
graphics on a form.
Creating a Graphics Object for a New Bitmap
You don’t have to set a Graphics object to the client area of a form or control; you
can also set a Graphics object to a bitmap that exists only in memory. For performance
reasons, you might want to use a memory bitmap to store temporary images or
as a place to build complex graphics before sending them to a visible element (such
as a form or control). To do this, you first have to create a new bitmap.
To create a new bitmap, you dimension a variable to hold a reference to the new
bitmap, using the following syntax:
variable = New Bitmap(width, height, pixelformat)
The width and height arguments are exactly what they appear to be: the width and
height of the new bitmap. The pixelformat argument, however, is less intuitive. This
argument determines the bitmap’s color depth and might also specify whether the
bitmap has an alpha layer (used for transparent portions of bitmaps). Table 18.1 lists
a few of the common values for pixelformat. (See Visual Basic’s online Help for the
complete list of values and their meanings.)
To create a new bitmap that’s 640 pixels wide by 480 pixels tall and that has a pixel
depth of 24 bits, for example, you could use this statement:
objMyBitMap = New Bitmap(640, 480, Drawing.Imaging.PixelFormat.Format24bppRgb)
392 HOUR 18: Working with Graphics
By the
Way
TABLE 18.2 Possible Values for DashStyle
Value Description
Dash Specifies a line consisting of dashes.
DashDot Specifies a line consisting of a pattern of dashes and dots.
DashDotDot Specifies a line consisting of alternating dashes and double
dots.
Dot Specifies a line consisting of dots.
Solid Specifies a solid line.
Custom Specifies a custom dash style. The Pen object contains
properties that can be used to define the custom line.
After the bitmap is created, you can create a Graphics object that references the
bitmap by using the FromImage() method, like this:
objGraphics = Graphics.FromImage(objMyBitMap)
Now any drawing or printing done using objGraphics would be performed on the
memory bitmap. For the user to see the bitmap, you’d have to send the bitmap to a
form or control. You’ll do this later in this hour in the section “Persisting Graphics on
a Form.”
When you’re finished with a Graphics object, call its Dispose() method to
ensure that all resources used by the Graphics object are freed.
Working with Pens
A pen is an object that defines characteristics of a line. Pens are used to define color,
line width, and line style (solid, dashed, and so on). Pens are used with almost all the
drawing methods you’ll learn about in this hour.
Visual Basic supplies a number of predefined pens, and you can also create your own.
To create your own pen, use the following syntax:
penVariable = New Pen(color, width)
After a pen is created, you can set its properties to adjust its appearance. For example,
all Pen objects have a DashStyle property that determines the appearance of
lines drawn with the pen. Table 18.2 lists the possible values for DashStyle.
Using System Colors 393
The enumeration for DashStyle is part of the Drawing.Drawing2D namespace.
Therefore, to create a new, dark blue pen that draws a dotted line, you would use
code like the following:
Dim objMyPen As Pen
objMyPen = New Pen(Drawing.Color.DarkBlue, 3)
objMyPen.DashStyle = Drawing.Drawing2D.DashStyle.Dot
The 3 passed as the second argument to create the new pen defines the pen’s width—
in pixels.
Visual Basic includes many standard pens, which are available via the
System.Drawing.Pens class, as in
objPen = System.Drawing.Pens.DarkBlue
When drawing using the techniques discussed shortly, you can use custom pens or
system-defined pens—it’s your choice.
Using System Colors
At some point, you might have changed your Windows theme, or perhaps you
changed the image or color of your desktop. What you might not be aware of is that
Windows enables you to customize the colors of almost all Windows interface elements.
The colors that Windows allows you to change are called system colors. To
change your system colors, right-click the desktop, and choose Personalize from the
shortcut menu to display the Personalize Appearance and Sounds page. Next, click the
Window Color link to display the Window Color and Appearance dialog box shown in
Figure 18.1. In this dialog box, you click an item in the picture whose color you want
to change, and then you choose a new color at the bottom. (If you’re running a version
of Windows other than Windows 7, your dialog box might be slightly different.)
When you change a system color by using the Window Color and Appearance dialog
box, all loaded applications should change their appearance to match your selection.
In addition, when you start any new application, it should also match its appearance
to your selection. If you had to write code to manage this behavior, you’d have to
write a lot of code, and you’d be justified in avoiding the whole mess. However, making
an application adjust its appearance to match the user’s system color selections is
actually easy, so there’s no reason not to do it. For the most part, it’s automatic, with
controls that you add to a form.
To designate that an interface color should stay in sync with a user’s system colors,
you assign a system color to a color property of the item in question, as shown in
Figure 18.2. If you wanted to ensure that the color of a button matches the user’s system
color, for example, you would assign the system color Control to the BackColor
property of the Button control. Table 18.3 lists the most common system colors you
can use. For a complete list, consult the online Help.
394 HOUR 18: Working with Graphics
FIGURE 18.1
The Window
Color and
Appearance dialog
box lets you
select the colors
of most Windows
interface elements.
FIGURE 18.2
System colors
are assigned
from within the
System palette
tab.
TABLE 18.3 System Colors
Enumeration Description
ActiveCaption The color of the background of the active caption bar (title
bar).
ActiveCaptionText The color of the text of the active caption bar (title bar).
Control The color of the background of push buttons and other 3D
elements.
ControlDark The color of shadows on a 3D element.
Using System Colors 395
TABLE 18.3 System Colors
Enumeration Description
ControlLight The color of highlights on a 3D element.
ControlText The color of the text on buttons and other 3D elements.
Desktop The color of the Windows desktop.
GrayText The color of the text on a user interface element when it’s
disabled or dimmed.
Highlight The color of the background of highlighted text. This
includes selected menu items as well as selected text.
HighlightText The color of the foreground of highlighted text. This
includes selected menu items as well as selected text.
InactiveBorder The color of an inactive window border.
InactiveCaption The color of the background of an inactive caption bar.
InactiveCaptionText The color of the text of an inactive caption bar.
Menu The color of the menu background.
MenuText The color of the menu text.
Window The color of the background in a window’s client area.
When a user changes a system color using the Window Color and Appearance dialog
box, Visual Basic automatically updates the appearance of objects that use system
colors. You don’t have to write a single line of code to do this. Fortunately, when you
create new forms and add controls to forms, Visual Basic automatically assigns the
proper system color to the appropriate properties, so you don’t usually have to mess
with them.
Be aware that you aren’t limited to assigning system colors to their logically associated
properties. You can assign system colors to any color property you want, and you
can also use system colors when drawing. This enables you to draw custom interface
elements that match the user’s system colors, for example. Be aware, however, that if
you do draw with system colors, Visual Basic doesn’t update the colors automatically
when the user changes system colors; you would have to redraw the elements with
the new system colors. In addition, if you apply system colors to properties that aren’t
usually assigned system colors, you run the risk of displaying odd color combinations,
such as black on black, depending on the user’s color settings.
396 HOUR 18: Working with Graphics
By the
Way
Square Rectangle
Circle Ellipse
FIGURE 18.3
Rectangles are
used to define
the boundaries
of most shapes.
Users don’t change their system colors just for aesthetic purposes. I work with a
programmer who is color-blind. He’s modified his system colors so that he can
see things better on the screen. If you don’t allow your applications to adjust to
the user’s color preferences, you might make using your program unnecessarily
difficult, or even impossible, for someone with color blindness or visual acuity
issues.
Working with Rectangles
Before learning how to draw shapes, you need to understand the concept of a rectangle
as it relates to Visual Basic programming. A rectangle is a structure used to hold
bounding coordinates used to draw a shape. A rectangle isn’t necessarily used to
draw a rectangle (although it can be). Obviously, a square can fit within a rectangle.
However, so can circles and ellipses. Figure 18.3 illustrates how most shapes can be
bound by a rectangle.
To draw most shapes, you must have a rectangle. The rectangle you pass to a drawing
method is used as a bounding rectangle. The proper shape (circle, ellipse, and so
on) is always drawn within the confines of the bounding rectangle. Creating a rectangle
is easy. First, you dimension a variable as Rectangle, and then you set the X,
Y, Width, and Height properties of the object variable. The X, Y value is the coordinate
of the upper-left corner of the rectangle. The Height and Width properties are
self-explanatory.
The following code creates a rectangle that has its upper-left corner at coordinate 0,0,
has a width of 100, and height of 50. Note that this code simply defines a rectangle in
code; it doesn’t draw a rectangle to the screen:
Drawing Shapes 397
Dim rectBounding As New Rectangle()
rectBounding.X = 0
rectBounding.Y = 0
rectBounding.Width = 100
rectBounding.Height = 50
The Rectangle object enables you to send the X, Y, Height, and Width values as part
of its initialize construct. Using this technique, you could create the same rectangle
with only a single line of code:
Dim rectBounding as New Rectangle(0,0,100,50)
You can do a number of things with a rectangle after it’s defined. Perhaps the most
useful is the capability to enlarge or shrink the rectangle with a single statement. You
enlarge or shrink a rectangle using the Inflate() method. Here’s the most common
syntax of Inflate():
object.Inflate(changeinwidth, changeinheight)
When called this way, the rectangle width is enlarged (the left side of the rectangle
remains in place), and the height is enlarged (the top of the rectangle stays in place).
To leave the height or width unchanged, pass 0 as the appropriate argument. To
shrink a side, specify a negative number.
If you’re planning to do much drawing, you’ll use a lot of Rectangle objects, so I
strongly suggest that you learn as much about them as you can.
Drawing Shapes
Now that you’ve learned about the Graphics object, pens, and rectangles, you’ll
probably find drawing shapes to be fairly simple. You draw shapes by calling methods
of a Graphics object. Most methods require a rectangle, which is used as the
shape’s bounding rectangle, as well as a pen. In this section, you’ll learn what you
need to do to draw different shapes.
I’ve chosen to discuss only the most commonly drawn shapes. The Graphics
object contains many methods for drawing additional shapes.
By the
Way
Drawing Lines
To draw lines, you use the DrawLine() method of the Graphics object. DrawLine() is
one of the few drawing methods that doesn’t require a rectangle. The syntax for
DrawLine() is
398 HOUR 18: Working with Graphics
object.DrawLine(pen, x1, y1, x2, y2)
As previously discussed, object refers to a Graphics object, and pen refers to a Pen
object. x1, y1 is the coordinate of the line’s starting point, whereas x2, y2 is the
coordinate of the ending point; Visual Basic draws a line between the two points,
using the specified pen.
Drawing Rectangles
To draw rectangles (and squares, for that matter), you use the DrawRectangle()
method of a Graphics object. As you might expect, DrawRectangle() accepts a pen
and a rectangle. Here’s the syntax for calling DrawRectangle() in this way:
object.DrawRectangle(pen, rectangle)
If you don’t have a Rectangle object (and you don’t want to create one), you can call
DrawRectangle() by using the following format:
object.DrawRectangle(pen, X, Y, width, height)
Drawing Circles and Ellipses
You draw circles and ellipses by calling the DrawEllipse() method. If you’re familiar
with geometry, you know that a circle is simply an ellipse that has the same height
and width. This is why no specific method exists for drawing circles: DrawEllipse()
works perfectly. Like the DrawRectangle() method, DrawEllipse() accepts a pen
and a rectangle. The rectangle is used as a bounding rectangle. The width of the rectangle
is the width of the ellipse, and the height of the rectangle is the height of the
ellipse. DrawEllipse() has the following syntax:
object.DrawEllipse(pen, rectangle)
If you don’t have a Rectangle object defined (and you don’t want to create one), you
can call DrawEllipse() with this syntax:
object.DrawEllipse(pen, X, Y, Width, Height)
Clearing a Drawing Surface
To clear the surface of a Graphics object, call the Clear()method, passing it the
color to paint the surface like this:
objGraphics.Clear(Drawing.SystemColors.Control)
Drawing Text 399
Drawing Text
Drawing text on a Graphics object is similar to drawing a shape. The method name
even contains the word Draw, in contrast to Print. To draw text on a Graphics object,
call the DrawString() method. The basic format for DrawString() looks like this:
object.DrawString(stringoftext, font, brush, topX, leftY)
A few of these items are probably new to you. The argument stringoftext is selfexplanatory:
It’s the string you want to draw on the Graphics object. The topX and
leftY arguments represent the coordinate at which drawing will take place; they represent
the upper-left corner of the string, as illustrated in Figure 18.4.
The arguments brush and font aren’t so obvious. Both arguments accept objects. A
brush is similar to a pen, but whereas a pen describes the characteristics of a line, a
brush describes the characteristics of a fill. For example, both pens and brushes have
a color. But where pens have an attribute for defining a line style such as dashed or
solid, a brush has an attribute for a fill pattern such as solid, hatched, weave, or trellis.
When you draw text, a solid brush is usually sufficient. You can create brushes in
much the same way as you create pens, or you can use one of the standard brushes
available from the System.Drawing.Brushes class.
A Font object defines characteristics used to format text, including the character set
(Times New Roman, Courier, and so on), size (point size), and style (bold, italic, normal,
underlined, and so on). To create a new Font object, you could use code such as
the following:
Dim objFont As Font
objFont = New System.Drawing.Font(“Arial”, 30)
The text Arial in this code is the name of a font installed on my computer. In fact,
Arial is one of the few fonts installed on all Windows computers. If you supply the
name of a font that doesn’t exist on the machine at runtime, Visual Basic uses a
default font that it thinks is the closest match to the font you specified. The second
parameter is the point size of the text. If you want to use a style other than normal,
you can provide a style value as a third parameter, like this (note the logical or, as
X, Y
The coordinates are in reference to the upper-left corner of the text.
FIGURE 18.4
The coordinate
specified in
DrawString()
represents the
upper-left corner
of the printed
text.
400 HOUR 18: Working with Graphics
By the
Way
discussed in Hour 12, “Performing Arithmetic, String Manipulation, and Date/Time
Adjustments”):
objFont = New System.Drawing.Font(“Arial Black”, 30, _
FontStyle.Bold or FontStyle.Italic)
In addition to creating a Font object, you can use the font of an existing object, such
as a form. For example, the following statement prints text to a Graphics object,
using the font of the current form:
objGraphics.DrawString(“This is the text that prints!”, Me.Font, _
System.Drawing.Brushes.Azure, 0, 0)
Persisting Graphics on a Form
Sometimes you will find it necessary to use the techniques discussed in this hour to
draw to a form. However, you might recall from earlier hours that when you draw to
a form (actually, you draw to a Graphics object that references a form), the things
you draw aren’t persisted. The next time the form paints itself, the drawn elements
disappear. If the user minimizes the form or obscures the form with another window,
for example, the next time the form is painted, it will be missing all drawn elements
that were obscured. You can use a couple of approaches to deal with this behavior:
. Place all code that draws to the form in the form’s Paint event.
. Draw to a memory bitmap, and copy the contents of the memory bitmap to the
form in the form’s Paint event.
If you’re drawing only a few items, placing the drawing code in the Paint event
might be a good approach. However, consider a situation in which you have a lot of
drawing code. Perhaps the graphics are drawn in response to user input, so you can’t
re-create them all at once. In these situations, the second approach is clearly better.
Building a Graphics Project Example
Now you’ll build a project that uses the skills you’ve learned to draw to a form. In this
project, you’ll use the technique of drawing to a memory bitmap to persist the graphics
each time the form paints itself.
The project you’re about to build is perhaps the most difficult yet. I’ll explain each
step of the process, but I won’t spend time explaining the objects and methods
that have already been discussed.
Building a Graphics Project Example 401
To make things interesting, I’ve used random numbers to determine font size as well
as the X, Y coordinate of the text you’ll draw to the form. By far the easiest way to
create a random number in Visual Basic is to use the System.Random class. To generate
a random number within a specific range (such as a random number between 1
and 10), you follow these steps:
1. Create a new object variable of type System.Random.
2. Create a new instance of the Random class, passing a value to be used as the
seed to generate random numbers. I use Now.Millisecond, which causes a
pseudorandom number to be used as the seed, because this value changes
every millisecond and probably won’t be the same across repeated runs of the
application.
3. Call the Next() method of the Random class, passing it minimum and maximum
values. The Random class returns a random number that falls within the
specified range.
Start by creating a new Windows Application titled Persisting Graphics, and then follow
these steps to build the project:
1. Right-click Form1.vb in the Solution Explorer and choose Rename. Change the
name of the default form to MainForm.vb, and set the form’s Text property to
Persisting Graphics Example.
2. Your form’s interface will consist of a text box and a button. When the user
clicks the button, the contents of the text box will be drawn on the form in a
random location and with a random font size. Add a new text box to your
form, and set its properties as follows:
3. Add a new button to the form, and set its properties as follows:
Time for the code to fly!
Property Value
Name txtInput
Location 56, 184
Size 100, 20
Property Value
Name btnDrawText
Location 162, 182
Text Draw Text
402 HOUR 18: Working with Graphics
FIGURE 18.5
Make sure that
your code
appears exactly
as it does here.
As mentioned earlier, all drawing will be performed through the use of a memory
bitmap, which then will be copied to the form. You’ll reference this bitmap
in multiple places, so you’ll make it a module-level variable.
4. Double-click the form to access its Load event. Then add the following statement
above the Form_Load procedure declaration; do not place this in the
form’s Load event!
Private m_objDrawingSurface As Bitmap
5. For the bitmap variable to be used, it must reference a Bitmap object. A good
place to initialize things is in the form’s Load event, so put your cursor back in
the Load event now, and enter the following code:
Randomize()
‘ Create a drawing surface with the same dimensions as the client
‘ area of the form.
m_objDrawingSurface = New Bitmap(Me.ClientRectangle.Width, _
Me.ClientRectangle.Height, _
Drawing.Imaging.PixelFormat.Format24bppRgb)
InitializeSurface()
Your procedure should now look like the one shown in Figure 18.5.
The first statement in this procedure initializes the random-number generator
(you’ll be using random numbers in another procedure). The next statement
creates a new bitmap in memory. Because the contents of the bitmap are to be
Building a Graphics Project Example 403
sent to the form, it makes sense to use the dimensions of the form’s client area
as the size of the new bitmap—which is exactly what you’ve done. The final
statement calls a procedure that you haven’t yet created.
6. Position the cursor at the end of the End Sub statement, and press Enter a few
times to create a few new lines. Now you’ll write code to initialize the bitmap.
The code clears the bitmap to the system color Control and then draws an
ellipse that has the dimensions of the bitmap. (I’ve added comments to the
code so that you can follow along with what’s happening; all the concepts in
this procedure have been discussed already.) Enter the following procedure in its
entirety:
Private Sub InitializeSurface()
Dim objGraphics As Graphics
Dim rectBounds As Rectangle
‘ Create a Graphics object that references the bitmap and clear it.
objGraphics = Graphics.FromImage(m_objDrawingSurface)
objGraphics.Clear(System.Drawing.SystemColors.Control)
‘ Create a rectangle the same size as the bitmap.
rectBounds = New Rectangle(0, 0, m_objDrawingSurface.Width, _
m_objDrawingSurface.Height)
‘ Reduce the rectangle slightly so the ellipse won’t appear on the
‘ border.
rectBounds.Inflate(-1, -1)
‘ Draw an ellipse that fills the form.
objGraphics.DrawEllipse(System.Drawing.Pens.Orange, rectBounds)
End Sub
Your procedure should now look like the one shown in Figure 18.6.
If you run your project now, you’ll find that nothing is drawn to the form. The
drawing is being done to a bitmap in memory, and you haven’t yet added the
code to copy the bitmap to the form. The place to do this is in the form’s Paint
event so that the contents of the bitmap are sent to the form every time the form
paints itself. This ensures that the items you draw always appear on the form.
7. Create an event handler for the form’s Paint event. First, choose MainForm
Events from the object drop-down list in the upper-left corner of the code editor.
Then select Paint from the event drop-down list in the upper-right corner. Add
the following code to the Paint event:
Dim objGraphics As Graphics
‘ You can’t modify e.Graphics directly.
objGraphics = e.Graphics
‘ Draw the contents of the bitmap on the form.
objGraphics.DrawImage(m_objDrawingSurface, 0, 0, _
m_objDrawingSurface.Width, _
m_objDrawingSurface.Height)
404 HOUR 18: Working with Graphics
FIGURE 18.6
Verify that your
code is entered
correctly.
The e parameter of the Paint event has a property that references the form’s
Graphics object. You can’t modify the Graphics object by using the e parameter,
however, because it’s read-only. This is why you’ve created a new Graphics
object to work with and then set the object to reference the form’s Graphics
object. The method DrawImage() draws the image in a bitmap to the surface of
a Graphics object, so the last statement simply sends the contents of the
bitmap that exists in memory to the form.
If you run the project now, you’ll find that the ellipse appears on the form. Furthermore,
you can cover the form with another window, or even minimize it,
and the ellipse will always appear on the form when it’s displayed again—the
graphics persist.
8. The last thing you’ll do is write code that draws the contents entered into the
text box on the form. The text will be drawn with a random size and location.
Return to the Form Designer, and double-click the button to access its Click
event. Add the following code:
Dim objGraphics As Graphics
Dim objFont As Font
Dim intFontSize As Integer
Dim intTextX As Integer
Dim intTextY As Integer
Dim objRandom As System.Random
‘ If no text has been entered, get out.
Building a Graphics Project Example 405
If txtInput.Text = ““ Then Exit Sub
‘ Create a graphics object using the memory bitmap.
objGraphics = Graphics.FromImage(m_objDrawingSurface)
‘ Initialize the Random object.
objRandom = New Random(Now.Millisecond)
‘ Create a random number for the font size. Keep it between 8 and 48.
intFontSize = objRandom.Next(8, 48)
‘ Create a random number for X coordinate of the text.
intTextX = objRandom.Next(0, Me.ClientRectangle.Width - 20)
‘ Create a random number for Y coordinate of the text.
intTextY = objRandom.Next(0, Me.ClientRectangle.Height - 20)
‘ Create a new font object.
objFont = New System.Drawing.Font(“Arial”, intFontSize, _
FontStyle.Bold Or FontStyle.Italic)
‘ Draw the user’s text.
objGraphics.DrawString(txtInput.Text, objFont, _
System.Drawing.Brushes.Red, intTextX, intTextY)
‘ Clean up.
objGraphics.Dispose()
‘ Force the form to paint itself. This triggers the Paint event.
Me.Invalidate()
The comments I’ve included should make the code self-explanatory. However, the last
statement bears discussing. The Invalidate() method of a form invalidates the
client rectangle. This operation tells Windows that the form’s appearance is no longer
accurate and that the form needs to be repainted. This, in turn, triggers the form’s
Paint event. Because the Paint event contains the code that copies the contents of
the memory bitmap to the form, invalidating the form causes the text to appear. If
you don’t call Invalidate() here, the text doesn’t appear on the form (but it is still
drawn on the memory bitmap).
If you draw elements that are based on the form’s size, you need to call
Invalidate() in the form’s Resize event; resizing a form doesn’t trigger the
form’s Paint event.
By the
Way
Your project is now complete! Click Save All on the toolbar to save your work, and
then press F5 to run the project. You’ll notice immediately that the ellipse is drawn
on the form. Type something into the text box and click the button. Click it again.
406 HOUR 18: Working with Graphics
FIGURE 18.7
Text is drawn on
a form, much as
ordinary
shapes are.
Each time you click the button, the text is drawn on the form by the same brush, but
with a different size and location, as shown in Figure 18.7.
Summary
You won’t need to add drawing capabilities to every project you create. However,
when you need the capabilities, you need the capabilities. In this hour, you learned the
basic skills for drawing to a graphics surface, which can be a form, control, memory
bitmap, or one of many other types of surfaces. You learned that all drawing is done
with a Graphics object. You now know how to create a Graphics object for a form or
control, and even how to create a Graphics object for a bitmap that exists in memory.
Most drawing methods require a pen and a rectangle, and you can now create rectangles
and pens using the techniques you learned in this hour. After learning about pens
and rectangles, you’ve found that the drawing methods themselves are pretty easy to
use. Even drawing text is simple when you have a Graphics object to work with.
Persisting graphics on a form can be a bit complicated, and I suspect this will confuse
many new Visual Basic programmers who try to figure it out on their own. However,
you’ve now built an example that persists graphics on a form, and you’ll be able to
leverage the techniques involved when you have to do this in your own projects.
I don’t expect you to be able to sit down for an hour and create an Adobe Photoshop
knockoff. However, you now have a solid foundation on which to build. If you want
to attempt a project that performs a lot of drawing, dig deeper into the Graphics
object.
Workshop 407
Q&A
Q. What if I need to draw a lot of lines, one starting where another ends? Do I
need to call DrawLine() for each line?
A. The Graphics object has a method called DrawLines(), which accepts a series
of points. The method draws lines connecting the sequence of points.
Q. Is there a way to fill a shape?
A. The Graphics object includes methods that draw filled shapes, such as
FillEllipse() and FillRectangle().
Workshop
Quiz
1. What object is used to draw to a surface?
2. To set a Graphics object to draw to a form directly, you call what method of
the form?
3. What object defines the characteristics of a line? A fill pattern?
4. How do you make a color property adjust with the user’s Windows settings?
5. What object is used to define the boundaries of a shape to be drawn?
6. What method do you call to draw an ellipse? A circle?
7. What method do you call to print text on a graphics surface?
8. To ensure that graphics persist on a form, they must be drawn on the form in
what event?
Answers
1. The Graphics object
2. The CreateGraphics() method
3. Lines are defined by Pen objects; fill characteristics are defined by Brush
objects.
408 HOUR 18: Working with Graphics
4. Use System Colors.
5. A Rectangle object
6. Both shapes are drawn with the DrawEllipse() method.
7. The DrawString() method
8. The form’s Paint event
Exercises
1. Modify the example in this hour to use a font other than Arial. If you’re not
sure what fonts are installed on your computer, click the Start menu and
choose Settings, Control Panel. Click the Appearance and Personalization link,
and you’ll find a link to the system fonts.
2. Create a project that draws an ellipse that fills the form, much like the one you
created in this hour. However, draw the ellipse directly to the form in the Paint
event. Make sure that the ellipse is redrawn when the form is sized. (Hint:
Invalidate the form in the form’s Resize() event.)
Using the OpenFileDialog and SaveFileDialog Controls 409
HOUR 19
Performing File Operations
What You’ll Learn in This Hour:
. Using the OpenFileDialog and SaveFileDialog controls
. Manipulating files with System.IO.File
. Manipulating directories with System.IO.Directory
It’s difficult to imagine any application other than a tiny utility program that doesn’t
use the file system. In this hour, you’ll learn how to use controls to make it easy for a
user to browse and select files. In addition, you’ll learn how to use the
System.IO.File and System.IO.Directory objects to manipulate the file system
more easily than you might think. Using these objects, you can delete files and directories,
move them, rename them, and more. These objects are powerful, so remember:
Play nice!
Using the OpenFileDialog and
SaveFileDialog Controls
In Hour 1, “Jumping in with Both Feet: A Visual Basic 2010 Programming Tour,” you
used the OpenFileDialog control to enable a user to browse for pictures to display in
your Picture Viewer program. In this section, you’ll move beyond those basics to
learn important details about working with the OpenFileDialog, as well as its sister
control, the SaveFileDialog.
You’ll build a project to illustrate most of the file-manipulation concepts discussed in
this hour. Begin by creating a new Windows application called Manipulating Files,
and then follow these steps:
1. Right-click Form1.vb in the Solution Explorer, choose Rename, and change the
name of the default form to MainForm.vb. Next, set the form’s Text property
to Manipulating Files.
410 HOUR 19: Performing File Operations
FIGURE 19.1
The
OpenFileDia
log control is
used to browse
for a file.
2. Add a new text box to the form, and set its properties as shown in the following
table:
Using the OpenFileDialog Control
The OpenFileDialog control is used to display a dialog box that enables the user to
browse and select a file, as shown in Figure 19.1. It’s important to note that usually
the OpenFileDialog doesn’t actually open a file, but it enables a user to select a file
so that it can be opened by code within the application.
Add a new OpenFileDialog control to your project now by double-clicking the
OpenFileDialog item in the toolbox. The OpenFileDialog doesn’t have an interface
per se, so it appears in the area below the form rather than on it, as shown in Figure
19.2. For the user to browse for files, you have to manipulate the OpenFileDialog,
using its properties and methods.
Property Value
Name txtSource
Location 95, 8
Size 184, 20
Using the OpenFileDialog and SaveFileDialog Controls 411
FIGURE 19.2
The Open File
dialog box is
hosted below
the form, not
on it.
Property Value
Name btnOpenFile
Location 9, 6
Size 80, 23
Text Source:
You’ll add a button to the form that, when clicked, enables a user to locate and select
a file. If the user selects a file, the filename is placed in the text box you’ve created.
1. Add a button to the form, and set its properties as follows:
2. Double-click the button, and add the following code to its Click event:
OpenFileDialog1.InitialDirectory = “C:\”
OpenFileDialog1.Title = “Select a File”
OpenFileDialog1.FileName = ““
The first statement specifies the directory to display when the dialog box is first
shown. If you don’t specify a directory for the InitialDirectory property, the active
system directory is used (for example, the last directory browsed to with a different
Open File dialog box).
412 HOUR 19: Performing File Operations
By the
Way
The Title property of the OpenFileDialog determines the text displayed in the title
bar of the Open File dialog box. If you don’t specify text for the Title property,
Visual Basic displays the word Open in the title bar.
The FileName property is used to return the name of the chosen file. If you don’t set
this to an empty string before showing the Open File dialog box, the name of the
control is used by default—not a desirable result.
Creating File Filters
Different types of files have different extensions. The Filter property determines
what types of files appear in the Open File dialog box (refer to Figure 19.1). A filter is
specified in the following format:
Description|*.extension
The text that appears before the pipe symbol (|) describes the file type on which to filter,
whereas the text after the pipe symbol is the pattern used to filter files. For example,
to display only Windows bitmap files, you could use a filter such as the following:
control.Filter = “Windows Bitmaps|*.bmp”
You can specify more than one filter type. To do so, add a pipe symbol between the
filters, like this:
control.Filter = “Windows Bitmaps|*.bmp|JPEG Files|*.jpg”
You want to restrict your Open File dialog box to show only text files, so enter this
statement in your procedure:
OpenFileDialog1.Filter = “Text Files (*.txt)|*.txt”
When you have more than one filter, you can specify which filter appears selected by
default by using the FilterIndex property. Although you’ve specified only one filter
type in this example, it’s still a good idea to designate the default filter, so add this
statement to your procedure:
OpenFileDialog1.FilterIndex = 1
Unlike most other collections, the FilterIndex property is 1-based, not 0-based,
so 1 is the first filter listed.
Showing the Open File Dialog Box
Finally, you need to show the Open File dialog box and take action based on whether
the user selects a file. The ShowDialog() method of the OpenFileDialog control acts
much like the method of forms by the same name, returning a result that indicates
the user’s selection in the dialog box.
Using the OpenFileDialog and SaveFileDialog Controls 413
Did you
Know?
By the
Way
Enter the following statements into your procedure:
If OpenFileDialog1.ShowDialog() <> Windows.Forms.DialogResult.Cancel Then
txtSource.Text = OpenFileDialog1.FileName
Else
txtSource.Text = ““
End If
This code just places the selected filename into the text box txtSource. If the user
clicks Cancel, the contents of the text box are cleared.
Press F5 to run the project, and click the button. You get the same dialog box shown
earlier in Figure 19.1 (with different files and directories, of course). Select a text file
and click Open. Visual Basic places the name of the file into the text box.
By default, the OpenFileDialog doesn’t let the user enter a filename that doesn’t
exist. You can override this behavior by setting the CheckFileExists property
of the OpenFileDialog to False.
The OpenFileDialog control can allow the user to select multiple files. It’s rare
that you need to do this (I don’t recall ever needing this capability in one of my
projects), so I won’t go into the details here. If you’re interested, take a look at
the Multiselect property of the OpenFileDialog in the Help text.
The OpenFileDialog control makes allowing a user to browse and select a file almost
trivial. Without this component, you would have to write an astounding amount of
difficult code and probably still wouldn’t come up with all the functionality supported
by this control.
Using the SaveFileDialog Control
The SaveFileDialog control is similar to the OpenFileDialog control, but it’s used to
allow a user to browse directories and specify a file to save, rather than open. Again,
it’s important to note that the SaveFileDialog control doesn’t actually save a file; it’s
used to allow a user to specify a filename to save. You have to write code to do something
with the filename returned by the control.
414 HOUR 19: Performing File Operations
Property Value
Name txtDestination
Location 95, 34
Size 184, 20
You’ll use the SaveFileDialog control to let the user specify a filename. This filename
will be the target of various file operations that you’ll learn about later in this
hour. Follow these steps to create the Save File dialog box:
1. Create a new text box on your form, and set its properties as follows:
2. Now you’ll create a button that, when clicked, enables the user to specify a filename
by which to save a file. Add a new button to the form, and set its properties
as shown in the following table:
3. Of course, none of this will work unless you add a Save File dialog box. Doubleclick
the SaveFileDialog item in the toolbox to add a new control to the project.
4. Double-click the new button you just created (btnSaveFile), and add the following
code to its Click event:
SaveFileDialog1.Title = “Specify Destination Filename”
SaveFileDialog1.Filter = “Text Files (*.txt)|*.txt”
SaveFileDialog1.FilterIndex = 1
SaveFileDialog1.OverwritePrompt = True
The first three statements set properties identical to those of the
OpenFileDialog. The OverwritePrompt property, however, is unique to the
SaveFileDialog. When this property is set to True, Visual Basic asks users to
confirm their selections when they choose a file that already exists, as shown
in Figure 19.3. I highly recommend that you prompt the user about replacing
files by ensuring that the OverwritePrompt property is set to True.
Property Value
Name btnSaveFile
Location 9, 31
Size 80, 23
Text Destination:
By the
Way If you want the Save File dialog box to prompt users when the file they specify
doesn’t exist, set the CreatePrompt property of the SaveFileDialog control to
True.
Manipulating Files with the File Object 415
FIGURE 19.3
It’s a good idea
to get confirmation
before
replacing an
existing file.
5. The last bit of code you need to add places the selected filename in the
txtDestination text box. Enter the code as shown here:
If SaveFileDialog1.ShowDialog() <> Windows.Forms.DialogResult.Cancel Then
txtDestination.Text = SaveFileDialog1.FileName
End If
Press F5 to run the project, and then click each of the buttons and select a file.
When you’re satisfied that your selections are being sent to the appropriate text
box, stop the project and save your work. If your selected filenames aren’t being
sent to the proper text box, compare your code against the code I’ve provided.
The OpenFileDialog and SaveFileDialog controls are similar in design and
appearance, but each serves a specific purpose. You’ll be using the interface you’ve
just created throughout the rest of this hour.
Manipulating Files with the File Object
Visual Basic includes a powerful namespace called System.IO (the IO object acts like
an object property of the System namespace). Using various properties, methods, and
object properties of System.IO, you can do just about anything you can imagine with
the file system. In particular, the System.IO.File and System.IO.Directory objects
provide you with extensive file and directory (folder) manipulation capabilities.
In the following sections, you’ll continue to expand the project you’ve created. You’ll
write code that manipulates the selected filenames by using the OpenFileDialog and
SaveFileDialog controls.
416 HOUR 19: Performing File Operations
Watch
Out! The code you’re about to write in the following sections is “the real thing.” For
example, the code for deleting a file really does delete a file. Don’t forget this as
you test your project; the files selected as the source and destination will be
affected by your actions. I provide the cannon, and it’s up to you not to shoot
yourself with it.
Determining Whether a File Exists
Before attempting any operation on a file, such as copying or deleting it, it’s a good
idea to make certain the file exists. For example, if the user doesn’t click the Source
button to select a file but instead types the name and path of a file into the text box,
the user could type an invalid or nonexistent filename. Attempting to manipulate a
nonexistent file could result in an exception—which you don’t want to happen.
Because you’ll work with the source file selected by the user in many routines, you
need to create a central function that can be called to determine whether the source
file exists. The function uses the Exists() method of the System.IO.File object to
determine whether the file exists.
Add the following function to your form class:
Private Function SourceFileExists() As Boolean
If Not (System.IO.File.Exists(txtSource.Text)) Then
MessageBox.Show(“The source file does not exist!”)
Return False
Else
Return True
End If
End Function
The SourceFileExists() method looks at the filename specified in the text box. If
the file exists, SourceFileExists() returns True; otherwise, it returns False.
Copying a File
Copying files is a common task. For example, you might want to create an application
that backs up important data files by copying them to another location. For the
most part, copying is pretty safe—as long as you use a destination filename that
doesn’t already exist. To copy files you use the Copy() method of the
System.IO.File class.
Now you’ll add a button to your form. When the user clicks this button, the file specified
in the source text box is copied to a new file with the name given in the destination
text box. Follow these steps to create the copy functionality:
1. Add a button to your form, and set its properties as shown in the following table:
Manipulating Files with the File Object 417
Did you
Know?
Property Value
Name btnCopyFile
Location 95, 71
Size 75, 23
Text Copy
2. Double-click the Copy button, and add the following code:
If Not (SourceFileExists()) Then Exit Sub
System.IO.File.Copy(txtSource.Text, txtDestination.Text)
MessageBox.Show(“The file has been successfully copied.”)
The Copy() method has two arguments. The first is the file that you want to copy,
and the second is the name and path of the new copy of the file. In this example,
you’re using the filenames selected in the two text boxes.
Press F5 to run the project, and test your copy code by following these steps:
1. Click the Source button and select a text file.
2. Click the Destination button to display the Save File dialog box. Don’t select an
existing file. Instead, type a new filename into the File Name text box and click
Save. If you’re asked whether you want to replace a file, click No and change
your filename; don’t use the name of an existing file.
3. Click Copy to copy the file.
After you see the message box telling you the file was copied, you can use Explorer to
locate the new file and open it. Stop the project and save your work before continuing.
Moving a File
When you move a file, it’s taken out of its current directory and placed in a new one.
You can specify a new name for the file or use its original name. You use the Move()
method of the System.IO.File object to move a file. Follow the steps listed next to
create a button on your form that moves the selected source file to the path and the
filename selected as the destination.
I recommend that you use Notepad to create a text file, and use this temporary
text file when testing from this point forward. This code, as well as the rest of the
examples presented in this hour, can permanently alter or destroy a file.
418 HOUR 19: Performing File Operations
Property Value
Name btnMove
Location 95, 100
Size 75, 23
Text Move
1. Add a new button to the form, and set its properties as follows:
2. Double-click the Move button, and add the following code to its Click event:
If Not (SourceFileExists()) Then Exit Sub
System.IO.File.Move(txtSource.Text, txtDestination.Text)
MessageBox.Show(“The file has been successfully moved.”)
Go ahead and press F5 to test your project. Select a file to move (again, I recommend
that you create a dummy file in Notepad) and supply a destination filename. When
you click Move, the file is moved to the new location and given the new name.
Remember, if you specify a filename for the destination that isn’t the same as that of
the source, the file is given the new name when it’s moved.
Renaming a File
When you rename a file, it remains in the same directory, and nothing happens to
its contents—the name is just changed to something else. Because the original file
isn’t altered, renaming a file isn’t as risky as performing an action such as deleting
it. Nevertheless, it’s frustrating trying to determine what happened to a file when it
was mistakenly renamed. To rename a file, use the Move() method of
System.IO.File, specifying a new filename but keeping the same path.
Deleting a File
Deleting a file can be a risky proposition. The Delete() method of System.IO.File
deletes a file permanently—it does not send the file to the Recycle Bin. For this reason,
take great care when deleting files. First and foremost, this means testing your code.
When you write a routine to delete a file, be sure to test it under many conditions.
For example, if you reference the wrong text box in this code, you would inadvertently
delete the wrong file! Users aren’t forgiving of such mistakes.
Follow these steps to add a button to your project that deletes the source file when
clicked. Remember: Be careful when testing this code.
Manipulating Files with the File Object 419
1. Add a button to the form, and set its properties as follows:
Retrieving a File’s Properties
Although many people don’t realize it, files have a number of properties, such as the
date the file was last modified. The easiest way to see these properties is to use the
Explorer. View the attributes of a file now by starting the Explorer, right-clicking any
file displayed in the Explorer, and choosing Properties. Explorer shows the File Properties
window, with information about the file (see Figure 19.4).
The System.IO.File object provides ways to get at most of the data displayed on the
General tab of the File Properties dialog box, shown in Figure 19.4. Some of this data
is available directly from the File object, whereas the FileAttributes object is used
to access other data.
Property Value
Name btnDelete
Location 95, 129
Size 75, 23
Text Delete
2. Double-click the button, and add the following code to its Click event:
If Not (SourceFileExists()) Then Exit Sub
If MessageBox.Show(“Are you sure you want to delete the source file?”, _
“MyApp”, MessageBoxButtons.YesNo , MessageBoxIcon.Question) = _
Windows.Forms.DialogResult.Yes Then
System.IO.File.Delete(txtSource.Text)
MessageBox.Show(“The file has been successfully deleted.”)
End If
Notice that you’ve included a message box to confirm the user’s intentions. It’s a
good idea to do this whenever you’re about to perform a serious action that can’t be
undone. In fact, the more information you can give the user, the better. For example,
I suggest that if this was production code (code meant for end users), you should
include the name of the file in the message box so that the user knows without a
doubt what the program intends to do. If you’re feeling brave, press F5 to run the
project, and then select a file and delete it.
Did you
Know? Instead of permanently deleting a file, you can send it to the Recycle Bin by using
the My object like this:
My.Computer.FileSystem.DeleteFile(“C:\test.txt”, _
FileIO.UIOption.AllDialogs, FileIO.RecycleOption.SendToRecycleBin)
420 HOUR 19: Performing File Operations
FIGURE 19.4
Visual Basic provides
a means
to easily obtain
most file properties.
TABLE 19.1 File Object Methods to Retrieve Data Information
Property Description
GetCreationTime Returns the date and time the file was
created.
GetLastAccessTime Returns the date and time the file was last
accessed.
GetLastWriteTime Returns the date and time the file was last
modified.
Getting Date and Time Information About a File
Getting the date the file was created, the last date it was accessed, and the last date it
was modified is easy. The System.IO.File object supports a method for each of these
dates. Table 19.1 lists the applicable methods and what they return.
Getting a File’s Attributes
A file’s attributes (see the bottom of the dialog box shown in Figure 19.4) aren’t available
as properties of the System.IO.File object. How you determine an attribute is
complicated. The GetAttributes() method of System.IO.File returns a Long. This
Long, in turn, acts as a set of flags for the various attributes. The method used to store
these values is called bit packing. Bit packing is pretty complicated and has to do with
Manipulating Files with the File Object 421
TABLE 19.2 Common File Attribute Flags
Attribute Meaning
Archive The file’s archive status. Applications use
this attribute to mark files for backup and
removal.
Directory The file is a directory.
Hidden The file is hidden and therefore isn’t
included in an ordinary directory listing.
Normal The file is normal and has no other
attributes set.
ReadOnly The file is a read-only file.
System The file is part of the operating system or
is used exclusively by the operating
system.
Temporary The file is a temporary file.
the binary method in which values are stored in memory and on disk. Teaching bit
packing is beyond the scope of this book. What I want to show you is how to determine
whether a certain flag is set in a value that is bit-packed.
The first step in determining the attributes is to get the Long containing the flags for
the file attributes. To do this, you would create a Long variable and call
GetAttributes(), like this:
Dim lngAttributes As Long
lngAttributes = System.IO.File.GetAttributes(“c:\test.txt”)
or use the short form, like this:
Dim lngAttributes As Long = System.IO.File.GetAttributes(“c:\test.txt”)
After you retrieve the file attributes flag into the variable lngAttributes, perform a
logical And on lngAttributes with one of the flags shown in Table 19.2 to determine
whether a particular attribute is set. This is sometimes called “Anding” a variable. For
example, to determine whether a file’s ReadOnly flag is set, you would use a statement
like this:
lngAttributes And IO.FileAttributes.ReadOnly
When you logically And a flag value with a variable, you get True if the variable contains
the flag and False otherwise.
422 HOUR 19: Performing File Operations
Writing Code to Retrieve a File’s Properties
Now that you know how to retrieve an object’s properties, you’ll modify your Picture
Viewer project so that the user can view file properties of a picture file he or she has displayed.
Start by opening the Picture Viewer project you last modified in Hour 15, “Debugging
Your Code,” and then follow these steps to add the file attributes functionality:
1. Add a new tool button to the Toolstrip (the toolbar) of the ViewerForm.vb form,
and set its name to tbbGetFileAttributes.
2. If you have downloaded the sample code, set the image to Properties.png. Next,
set the ToolTipText property to Get File Attributes.
The code you enter into the Click event of this button is a bit longer than most
of the code you’ve entered so far. Therefore, I’ll show the code in its entirety and
then explain what it does.
3. Double-click the new button, and add the following code to the button’s
Click event:
Dim strProperties As String
Dim lngAttributes As Long
If ofdSelectPicture.FileName = ““ Then Exit Sub
‘ Get the dates.
strProperties = “Created: “ & _
System.IO.File.GetCreationTime(ofdSelectPicture.FileName)
strProperties = strProperties & vbCrLf
strProperties = strProperties & “Accessed: “ & _
System.IO.File.GetLastAccessTime(ofdSelectPicture.FileName)
strProperties = strProperties & vbCrLf
strProperties = strProperties & “Modified: “ & _
System.IO.File.GetLastWriteTime(ofdSelectPicture.FileName)
‘ Get the file attributes.
lngAttributes = System.IO.File.GetAttributes(ofdSelectPicture.FileName)
‘ Use a binary AND to extract the specific attributes.
strProperties = strProperties & vbCrLf
strProperties = strProperties & “Normal: “ & _
CBool(lngAttributes And IO.FileAttributes.Normal)
strProperties = strProperties & vbCrLf
strProperties = strProperties & “Hidden: “ & _
CBool(lngAttributes And IO.FileAttributes.Hidden)
strProperties = strProperties & vbCrLf
strProperties = strProperties & “ReadOnly: “ & _
CBool(lngAttributes And IO.FileAttributes.ReadOnly)
strProperties = strProperties & vbCrLf
strProperties = strProperties & “System: “ & _
CBool(lngAttributes And IO.FileAttributes.System)
Manipulating Files with the File Object 423
Did you
Know?
strProperties = strProperties & vbCrLf
strProperties = strProperties & “Temporary File: “ & _
CBool(lngAttributes And IO.FileAttributes.Temporary)
strProperties = strProperties & vbCrLf
strProperties = strProperties & “Archive: “ & _
CBool(lngAttributes And IO.FileAttributes.Archive)
MessageBox.Show(strProperties, “Picture Viewer”)
A quick way to determine a file’s size is to use the built-in Visual Basic function
FileLen(), as in lngFileSize = FileLen(“c:\temp\test.txt”).
The first thing this procedure does is see whether the user is viewing a file. The place
to look is the OpenFileDialog control because that is where the filename was
obtained from the user. If the OpenFileDialog control has no filename, the user hasn’t
viewed a file yet.
All the file’s various properties are concatenated with the strProperties variable.
The system constant vbCrLf denotes a carriage return and a line feed, and concatenating
this into the string ensures that each property appears on its own line.
The first set of statements simply calls the GetCreateTime(), GetLastAccessTime(),
and GetLastWriteTime() methods to get the values of the date-related properties.
Next, the attributes are placed in a variable by way of the GetAttributes() method,
and the state of each attribute is determined. The CBool() functions are used so that the
words True and False appear, rather than the numeric results of the And operations.
Press F5 to run the project, open a picture file to display it, and then click the Get File
Attributes button on the toolbar. If you entered the code exactly as shown, the attributes
of the image file should appear in the text box as they do in Figure 19.5.
FIGURE 19.5
The
System.IO.
File object
enables you to
look at a file’s
properties.
424 HOUR 19: Performing File Operations
To send a directory to the Recycle Bin, rather than permanently delete it, use the
My object like this:
My.Computer.FileSystem.DeleteDirectory(“D:\OldDir”, _
FileIO.UIOption.AllDialogs, FileIO.RecycleOption.SendToRecycleBin, _
FileIO.UICancelOption.ThrowException)
Did you
Know?
Manipulating Directories with the
Directory Object
Manipulating directories (folders) is similar to manipulating files. However, instead of
using System.IO.File, you use System.IO.Directory. If any of these method calls
confuse you, refer to the previous section on System.IO.File for more detailed information.
The following are the method calls:
. To create a directory, call the CreateDirectory() method of
System.IO.Directory, and pass the name of the new folder, like this:
System.IO.Directory.CreateDirectory(“c:\my new directory”)
. To determine whether a directory exists, call the Exists() method of
System.IO.Directory and pass it the directory name in question, like this:
MsgBox(System.IO.Directory.Exists(“c:\temp”))
. To move a directory, call the Move() method of System.IO.Directory. The
Move() method takes two arguments. The first is the current name of the directory,
and the second is the new name and path of the directory. When you
move a directory, its contents are moved as well. The following illustrates a call
to Move():
System.IO.Directory.Move(“c:\current directory name”, _
“c:\new directory name”)
. Deleting directories is even more perilous than deleting files because when you
delete a directory, you also delete all files and subdirectories within the directory.
To delete a directory, call the Delete() method of System.IO.Directory,
and pass it the directory to delete. I can’t overstate that you have to be careful
when calling this method; it can get you in a lot of trouble. The following statement
illustrates deleting a directory:
System.IO.Directory.Delete(“c:\temp”)
Workshop 425
Summary
The OpenFileDialog and SaveFileDialog controls, coupled with System.IO,
enable you to do many powerful things with a user’s file system. In this hour, you
learned how to let a user browse and select a file for opening and how to let a user
browse and select a file for saving. Determining a user’s file selection is only the first
part of the process, however. You also learned how to manipulate files and directories,
including renaming, moving, and deleting, by using System.IO. Finally, you
learned how to retrieve a file’s properties and attributes.
With the techniques shown in this hour, you should be able to do most of what you’ll
need to do with files and directories. None of this material is difficult, but don’t be
fooled by the simplicity; use care whenever manipulating a user’s file system.
Q&A
Q. What if I want to perform an operation on a file, but something is preventing
the operation, such as the file being open or me lacking rights to the file?
A. All the method calls have one or more exceptions that can be thrown if the
method fails. These method calls are listed in the online Help. You can use the
techniques discussed in Hour 15 to trap the exceptions.
Q. What if the user types a filename into one of the file dialog boxes but doesn’t
include the extension?
A. By default, both file dialog controls have their AddExtension properties set to
True. When this property is set to True, Visual Basic automatically appends
the extension of the currently selected filter.
Workshop
Quiz
1. True or false: The Open File dialog box automatically opens a file.
2. What symbol is used to separate a filter description from its extension?
3. What object is used to manipulate files?
4. What arguments does System.IO.File.Copy() expect?
426 HOUR 19: Performing File Operations
5. How would you rename a file?
6. True or false: Files deleted with System.IO.File.Delete() are sent to the
Recycle Bin.
7. What object is used to manipulate folders?
Answers
1. False
2. The pipe symbol (|)
3. System.IO
4. The name and path of the source file and a name and path for the copy
5. Use the Move() method while retaining the path.
6. False. The files are permanently deleted.
7. System.IO.Directory
Exercises
1. Create a project that enables the user to select a file with the
OpenFileDialog control. Store the filename in a text box. Provide another
button that, when clicked, creates a backup of the file by making a copy of it
with the extension .bak.
2. Create a project with a text box on a form in which the user can type in a
three-digit file extension. Include a button that shows an Open File dialog box
when clicked, with the filter set to the extension that the user entered.
Working with the Registry 427
HOUR 20
Working with the Registry
and Text Files
What You’ll Learn in This Hour:
. Using My.Computer.Registry to create and delete Registry keys and values
. Using a StreamWriter object to open, read, and edit text files
. Modifying your Picture Viewer program to use a text file and the Registry
Text files have been around since the early days of computing, and even today they
are useful for storing data. For robust applications, a database is the way to go, but
for storing simple sets of data, it doesn’t get much easier than using a text file. In the
first edition of this book, I neglected to cover working with text files, thinking that
most users were moving to databases. After many emails from readers, I got the
point: Text files are still used regularly, and they aren’t going anywhere. This hour
teaches you the basics of creating, opening, reading, and editing text files.
Another common method of storing data—particularly user settings and program
configuration options—is the Windows Registry. The Registry is a database-like storage
entity in Windows that resembles a tree with nodes. Accessing the Registry is fast,
is handled through a consistent interface, and is often preferred over the old method
of using INI text files. In this hour, you’ll learn how to store data in and get data
from the Windows Registry.
Working with the Registry
The Windows Registry is a repository used to store application, user, and machinespecific
information. It’s the perfect place to store configuration data such as user
preferences, database connection strings, file locations, and more.
428 HOUR 20: Working with the Registry and Text Files
By the
Way
TABLE 20.1 Top Nodes of the Windows Registry
Node Description
HKEY_CLASSES_ROOT Contains information that associates file types with
programs and configuration data for COM components.
HKEY_CURRENT_USER Contains configuration information for the user currently
logged on to Windows.
HKEY_LOCAL_MACHINE Contains configuration information specific to the
computer, regardless of the user logged in.
HKEY_USERS Contains all user profiles on the computer. When a user
logs in, HKEY_CURRENT_USER is set as an alias to a
specific user in HKEY_USERS.
HKEY_CURRENT_CONFIG Contains information about the hardware profile used by
the local computer during startup.
Don’t pollute the Registry! I’m constantly amazed by the amount of junk that a
program will store in the Registry. Keep in mind that the Registry is not your personal
database. In fact, if your application uses a database, it’s often a better
idea to store information in the database.
Understanding the Structure of the Windows
Registry
The Registry is organized in a hierarchical structure—like a tree. The top nodes in the
tree (called hives) are predefined—you can’t add to, modify, or delete them. Table 20.1
lists the hives (top levels) of the Registry.
Under each hive listed in Table 20.1 are a number of keys. Figure 20.1 shows what the
Registry looks like on my computer. Notice how 10.0 is a subkey that belongs to the
VBExpress key, which is a subkey that belongs to the Microsoft key, which in turn is
a subkey of the Software key, which belongs to the HKEY_CURRENT_USER hive. Note
that while you can’t see the higher levels in the tree, you can see the entire path in
the status bar.
Keys can contain one or more values. In Figure 20.1, notice that the 10.0 key has
many values (they appear in the list view on the right). Keys are used to provide a
Working with the Registry 429
FIGURE 20.1
The Registry is a
hierarchical
structure of
hives, keys, and
values.
framework for storing data; values actually hold the data in question. Value items
have specific data types, although they are different from the data types in Visual
Basic. Table 20.2 lists the possible data types for Registry values.
By far, the most commonly used data type is the REG_SZ string data type. You can
store all sorts of things in a REG_SZ value, such as text (obviously), True, False, 0, 1,
and more. In fact, this is usually the only data type I use for my applications. When
saving Boolean values, I just format them as either 1 or 0.
TABLE 20.2 Common Registry Value Data Types
Data Type Description
REG_SZ The primary type of string data. It is used to store fixed-length
string data or other short text values.
REG_EXPAND_SZ An expandable string value that can hold system variables
whose values get resolved at runtime.
REG_MULTI_SZ Holds multiple text strings formatted as an array. Each
“element” string is terminated by a null character.
REG_BINARY Used to store binary data.
430 HOUR 20: Working with the Registry and Text Files
TABLE 20.3 Common Top-Node Properties of the Registry Object
Property What It’s Used to Access
ClassesRoot HKEY_CLASSES_ROOT
CurrentConfig HKEY_CURRENT_CONFIG
CurrentUser HKEY_CURRENT_USER
LocalMachine HKEY_LOCAL_MACHINE
Users HKEY_USERS
Accessing the Registry with
My.Computer.Registry
You can access the Windows Registry in two ways. The first (and easiest) is to use the
built-in Visual Basic functions GetSetting() and SaveSetting(). These functions
have serious limitations, however, including letting you manipulate keys and values
only in specific Visual Basic keys within the Registry. No self-respecting commercial
application would do this, and neither should your applications. I won’t teach you
these two functions. Instead, you’ll learn how to use the Registry object to manipulate
the Windows Registry like a pro.
The Registry object is an object property of My.Computer. When Microsoft first
released .NET, people were amazed by the power but confused by the complexity.
Harnessing the power of the .NET Framework often required digging through poorly
written Help text or exploring objects using the Object Browser. Microsoft realized this
was a problem and consequently added the My object. The My object is basically a
shortcut to other useful objects that aren’t so easy to get to on their own. The My
object makes it easy to retrieve information about your running application and the
user’s computer. One of the object properties available to the My object is the
Computer object, which is used to access objects that let you work with the user’s computer.
The Computer object has an object property called Registry, which gives you
direct access to the Windows Registry. You will use My.Computer.Registry to perform
all your Registry tasks.
Creating Registry Keys
The My.Computer.Registry object has a number of properties. Among these are
object properties that relate to the hives of the Registry already shown in Table 20.1.
Table 20.3 lists the properties that reference the Registry’s hives.
Creating Registry keys using My.Computer.Registry is a snap. First, you have to
identify the hive under which you want to create the key. When you know the hive,
Working with the Registry 431
you just call the CreateSubKey() method of the corresponding hive object property,
passing it the name of the key to create. For example, consider this statement:
My.Computer.Registry.CurrentUser.CreateSubKey(“UserSettings”)
This statement would create the key UserSettings under HKEY_CURRENT_USER. Realize
that an application rarely creates a key directly under a hive. You can use many
subkeys for each hive, but perhaps the most common is the \Software key. Most
applications create a corporate-named key under \Software and then create product
keys below the corporate subkey. For example, suppose that your company name is
CleverSoftware, you’re planning to ship the Picture Viewer program, and you want to
store some application settings in the Registry. (In fact, you will modify your Picture
Viewer to do this later in this hour.) You want to end up with a key structure that
looks like this:
HKEY_CURRENT_USER\Software\CleverSoftware\PictureViewer
Fortunately, the CreateSubKey() method enables you to specify multiple levels of keys
in one method call. To create this structure, you would use the following statement:
My.Computer.Registry.CurrentUser.CreateSubKey _
(“Software\CleverSoftware\PictureViewer”)
Visual Basic would parse this statement by first locating the hive HKEY_CURRENT_USER
and then looking for a \Software key. It would find one, because all Windows
machines have this key, but it would not overwrite this key. It would then look for
CleverSoftware. Assuming that it does not find this key, it would create it and the subkey
that you specified. Note that if Visual Basic finds an existing subkey that you
defined in your statement (all subkeys are separated by a backslash [\]), it does not
overwrite it.
Why HKEY_CURRENT_USER instead of HKEY_LOCAL_MACHINE? In general, it’s best
to save application settings in HKEY_CURRENT_USER so that each user who uses
your application can have his or her own settings. If you store your settings in
HKEY_LOCAL_MACHINE, the settings will be global to all users who run the application
from the computer in question. Also, some administrators restrict access to
HKEY_LOCAL_MACHINE, and your application will fail if it attempts to access
restricted keys.
By the
Way
Deleting Registry Keys
You can use two methods to delete a Registry key: DeleteSubKey() and
DeleteSubKeyTree(). DeleteSubKey() deletes a key and all its values as long as the
432 HOUR 20: Working with the Registry and Text Files
Did you
Know?
key contains no subkeys. DeleteSubKeyTree() deletes a key, its values, and all subkeys
and values found below it. Use this one with care!
Here’s a statement that could be used to delete the key created with the previous sample
code:
My.Computer.Registry.CurrentUser.DeleteSubKey _
(“Software\CleverSoftware\PictureViewer”)
DeleteSubKey throws an exception if the key you specify does not exist. Whenever
you write code to work with the Registry, try to account for the unexpected.
Getting and Setting Key Values
Creating and deleting keys is useful, but only in the sense that keys provide the structure
for the important data: the value items. You’ve already learned that keys can
have one or more value items and that value items are defined as a specific data
type. All that’s left is to learn the code used to manipulate Registry values.
Unfortunately, getting and setting key values isn’t as easy as defining keys. When
you define keys, the My.Computer.Registry object makes it easy to work with hives
by giving you an object property for each hive. There are properties for getting and
setting values for each of these hive properties, but they don’t work as expected. To
create a new value item, or to set the value of an existing value item, you use
My.Computer.Registry.SetValue(). The SetValue()method has the following
syntax:
SetValue(keypath, itemname, value)
Unfortunately, you have to specify the hive name in keypath, as you will see. Notice
that you do not specify the data type; Visual Basic sets the data type according to the
value that is passed to the method. For example, to create a RegistrationName
value item for the Registry key discussed in the preceding section, you would use a
statement like this:
My.Computer.Registry.SetValue _
(“HKEY_CURRENT_USER\Software\CleverSoftware\PictureViewer\”, _
“RegistrationName”, “James Foxall”)
This statement would produce a value item, as shown in Figure 20.2.
To change the value, you would call SetValue again, passing it the same key and
item name, but a different value—nice and easy!
To retrieve a value from the Registry, you use the GetValue method. This method also
requires a full hive/key path. The format of GetValue() is this:
Working with the Registry 433
FIGURE 20.2
Values appear
attached to
keys.
GetValue(keypath, itemname, defaultvalue)
The parameters keypath and itemname are the same as those used with SetValue().
Sometimes, when you go to retrieve a value from the Registry, the value and perhaps
even the key don’t exist. There are a number of reasons for this. Another application
might have deleted the value, the user might have manually deleted the value, or the
user might have restored a backup of his or her Registry from before the value was
created. The defaultvalue parameter is used to define what GetValue() returns if it
is unable to find the value item. This eliminates the need to catch an exception if the
value item is missing. The following statement displays the value in the
RegistrationName as created in the previous example:
MessageBox.Show(My.Computer.Registry.GetValue _
(“HKEY_CURRENT_USER\Software\CleverSoftware\PictureViewer\”, _
“RegistrationName”, ““))
Modifying Your Picture Viewer Project to Use the
Registry
In this section, you’ll modify your Picture Viewer project so that the user’s settings in
the Options dialog box are saved to the Registry. When the user first starts the Picture
Viewer program, the settings are loaded from the Registry. Start by opening the Picture
Viewer project you last worked on in Hour 19, “Performing File Operations.”
434 HOUR 20: Working with the Registry and Text Files
Displaying Options from the Registry
The first thing you need to do is show the current user’s settings when the Options
form is displayed. Follow these steps to display the options stored in the Registry:
1. Double-click OptionsForm.vb in the Solution Explorer to display the Options
form, and then double-click the form to access its Load event.
2. Right above the statement that declares the Load procedure, add the following
statement to declare a module-level constant:
Const c_strKeyName As String =
“HKEY_CURRENT_USER\Software\CleverSoftware\PictureViewer\”
3. Put the cursor back in the Load procedure. Notice that the Load event already
includes a statement to set the form’s icon. Add the following code statements
to the Load event, immediately following the existing statement:
txtUserName.Text = CStr(My.Computer.Registry.GetValue _
(c_strKeyName, “UserName”, ““))
chkPromptOnExit.Checked = CBool(My.Computer.Registry.GetValue _
(c_strKeyName, “PromptOnExit”, “0”))
If CStr(My.Computer.Registry.GetValue _
(c_strKeyName, “BackColor”, “Gray”)) = “Gray” Then
optBackgroundDefault.Checked = True
Else
optBackgroundWhite.Checked = True
End If
All this code should be familiar to you by now. The first statement you enter simply creates
a module-level constant with the full key path you’ll use to access the Registry.
Since you need this three times in this procedure alone, and it won’t change during
runtime, it makes sense to use a constant rather than hard-code the value on each line.
It should be a module-level constant because you’ll need it again in another procedure.
The first statement you enter into the Load event sets the value of the txtUserName
text box to the username stored in the Registry. The first time the Options form loads,
there is no entry in the Registry, so an empty string is used. Notice that the Registry
call is wrapped in CStr() so that whatever value you pull from the Registry will be
converted to a string, which is what a text box accepts. Because I had you turn on
Options Strict in Hour 11, “Using Constants, Data Types, Variables, and Arrays,” this
is required.
The second statement in the Load event sets the checked state of the Prompt on Exit
check box to the value stored in the Registry. If no value is found, as is the case the
Working with the Registry 435
first time the Options form is loaded, the Checked property is set to False. Again, you
have to wrap the result of GetValue() with a conversion function—in this case,
CBool()—to convert the value to a Boolean.
The next statement starts an If...End If construct that looks for a color name in
the Registry and sets the appropriate option button’s Checked property to True.
Because you’re comparing the Registry result to text, wrap the result in CStr() to cast
the result as a string.
Saving Options to the Registry
Now that the Options form displays the current values stored in the Registry, you can
add the code to save the changes the user makes to these values. Follow these steps:
1. Choose btnOK from the object drop-down list in the upper-left corner of the code
window.
2. Choose Click from the list of events in the upper-right corner of the code
window.
3. Enter the following code into the btnOK_Click event. Be sure to put the code
before the existing statement Me.Close():
My.Computer.Registry.SetValue _
(c_strKeyName, “UserName”, txtUserName.Text)
My.Computer.Registry.SetValue _
(c_strKeyName, “PromptOnExit”, chkPromptOnExit.Checked)
If optBackgroundDefault.Checked Then
My.Computer.Registry.SetValue _
(c_strKeyName, “BackColor”, “Gray”)
Else
My.Computer.Registry.SetValue _
(c_strKeyName, “BackColor”, “White”)
End If
This code is essentially the opposite of the code you entered in the Load event; it stores
the values of the controls in the Registry. You should be able to follow this code on
your own.
Using the Options Stored in the Registry
You’re now allowing the user to view and change the settings stored in the Registry,
but you’re not actually using the user’s preferences. Follow these steps to use the values
stored in the Registry:
436 HOUR 20: Working with the Registry and Text Files
1. Double-click ViewerForm.vb in the Solution Explorer window to display the
main Picture Viewer form in the designer.
2. Double-click the form to access its Load event.
3. The Load event currently contains six lines of code. Add the following statement
right after the third statement (place it right below the two statements
that set the X and Y label text):
Const c_strKeyName As String = _
“HKEY_CURRENT_USER\Software\CleverSoftware\PictureViewer\”
Notice how you’ve duplicated a constant. That’s fine for this example, but if
you wanted to ship this as a real product, you should declare the constant in a
global module so that it could be declared only once and be used throughout
the application.
4. The first statements to change are the following:
m_blnPromptOnExit = c_defPromptOnExit
mnuConfirmOnExit.Checked = m_blnPromptOnExit
Recall that you keep track of the Prompt on Exit flag as a module variable. The
first statement sets this flag to the constant you defined as the default value.
The second statement sets the checked state of the menu item to the variable.
5. Delete the statement m_blnPromptOnExit = c_defPromptOnExit, and replace
it with this:
m_blnPromptOnExit = CBool(My.Computer.Registry.GetValue _
(c_strKeyName, “PromptOnExit”, “0”))
This is almost identical to the statement you created in the Load event of the
Options form. It retrieves the Prompt on Exit flag from the Registry, but this
time it sets the module variable instead of a check box on the form.
6. Here’s the next statement you’ll replace:
m_objPictureBackColor = System.Drawing.SystemColors.Control
This sets the default back color of the picture box to the system color Control,
which by default is a shade of gray. Replace this statement with the following
code:
If CStr(My.Computer.Registry.GetValue _
(c_strKeyName, “BackColor”, “Gray”)) = “Gray” Then
m_objPictureBackColor = System.Drawing.SystemColors.Control
Else
m_objPictureBackColor = System.Drawing.Color.White
End If
Working with the Registry 437
Testing and Debugging Your Picture Viewer Project
Press F5 to run the project. Next, click the Options button on the toolbar to display
the Options form. Nothing looks different yet. Follow these steps to see the effect of
your new code:
1. In the User Name text box, enter your name.
2. Click the Prompt to Confirm Exit check box to check it.
3. Click the Appearance tab, and then click the White option button to select it.
4. Click OK to close the Options dialog box.
5. Click the Options button on the toolbar again to display the Options dialog
box. Notice that White is now chosen as the Default Picture Background color.
6. Click the General tab. Notice that your name is in the User Name text box and
that the Prompt to Confirm on Exit check box is selected.
7. Click OK to close the Options dialog box.
8. Close the Picture Viewer.
Notice that you weren’t prompted to confirm exiting. This occurs because the main
Picture Viewer form is not being updated to reflect the changes made to the Registry.
Now you’ll use the skills you learned for creating procedures to make your code work
properly. Follow these steps:
1. Double-click ViewerForm.vb in the Solution Explorer window to show the form
in the designer.
2. Double-click the form to show its Load event.
3. Highlight all the code except the first two statements, as shown in Figure 20.3,
and press Ctrl+X to cut the code.
4. Enter the following statement:
LoadDefaults()
5. Position the cursor at the end of the End Sub statement that completes the definition
of the frmViewer_Load event, and press Enter to create a new line.
6. Type the following statement, and press Enter:
Public Sub LoadDefaults()
7. Press Ctrl+V to paste the code you deleted from the Form_Load event. Your code
window should look like Figure 20.4.
You now have a procedure that you can call when the user saves new settings
to the Registry.
438 HOUR 20: Working with the Registry and Text Files
FIGURE 20.3
Cut the highlighted
code.
FIGURE 20.4
Procedures are
all about grouping
related sets
of code.
8. Double-click OptionsForm.vb in the Solution Explorer to display it in the
designer.
9. Double-click OK to access its Click event.
Reading and Writing Text Files 439
10. Enter the following statement right before the Me.Close() statement (after all
the code that saves the user’s values to the Registry):
ViewerForm.LoadDefaults()
11. Press F5 to run the project.
12. Click the Options button on the toolbar to display the Options form, and
change the default background color to Gray on the Appearance tab. When
you click OK to save the settings and close the Options form, the background of
the picture box changes to gray immediately.
The Registry is a powerful tool to have at your disposal—if used properly! In this section,
you learned all the necessary techniques to implement Registry functionality in
your applications.
To view your Registry, hold down the Shift key and right-click the desktop. You see
a shortcut menu with the item Open Command Window Here. (If you don’t see
this item, you probably aren’t holding down the Shift key.) When you click this
menu item, a command prompt appears. Type regedit and press Enter to launch
the Registry Editor. (Note that you can also type regedit in the Search box of the
Start menu as well.) Be careful. Making inappropriate changes to the Registry can
foul up your computer to the point where it won’t boot!
Did you
Know?
Reading and Writing Text Files
The Registry is a handy place to store user options and program configuration settings.
It’s not a good place, however, to store a lot of data such as a text document. If
you have a lot of text data to store and retrieve, a good old-fashioned text file is probably
the best place to put it (assuming that a real database such as Microsoft SQL is
not an option). Visual Basic includes classes that make it relatively easy to manipulate
text files: StreamWriter and StreamReader. Notice that reading and writing text
files are performed by two different objects, only one of which can access a file at any
given time. If you want to simultaneously read and write to a single file, you’re probably
better off using a real database.
Writing to a Text File
You write to text files by using the StreamWriter class. The first step of using this
class is to declare an object of type StreamWriter, like this:
Dim objFile As New System.IO.StreamWriter(“c:\test.txt”)
440 HOUR 20: Working with the Registry and Text Files
By the
Way
Did you
Know?
By the
Way
or like this:
Dim objFile As New System.IO.StreamWriter(“c:\test.txt”, True)
There are actually at least seven different forms of StreamWriter usage. I’m
showing you the most common, but if you plan to do serious work with text files,
you should read the Microsoft Developer Network (MSDN) document on the
StreamWriter class.
As you can see, the second parameter is optional (it is omitted in the first example),
and it determines whether you want to append to the text file if it already exists. If
you omit this second parameter or supply False as its value, a new text file is created.
If the text file already exists, it gets replaced with a new file of the same name.
If you pass True, as in the second example, the file is opened, and any write operations
you perform on the file are tacked on to the end of the file.
If you pass a file path/filename that doesn’t exist, Visual Basic creates a new
text file for you when you write data to the StreamWriter object. Also, be aware
that you need access to your C: drive when you run this code or you will receive
an error.
After you have an object that points to a StreamWriter object, you can store data in
the text file, using one of the following two methods:
. WriteLine() sends a single line of text to the file and automatically appends a
carriage return to the end of the line. Each call to WriteLine() creates a new line.
. Write() sends data to the file but does not automatically append a carriage
return to create a new line.
These two methods are best understood by example. Consider the following code
snippet:
Dim objFile As New System.IO.StreamWriter(“c:\test.txt”)
objFile.WriteLine(“text1”)
objFile.WriteLine(“text2”)
objFile.WriteLine(“text3”)
objFile.Close()
This snippet would produce the following data in the text file:
text1
text2
text3
Notice the last statement, objFile.Close(). It’s vital that you close a text file
when you’re finished with it, and the Close() method does this. In addition, you
should also call objFile.Dispose() to make sure that the file is fully released.
Reading and Writing Text Files 441
Now, consider the same code snippet that uses Write() instead of WriteLine():
Dim objFile As New System.IO.StreamWriter(“c:\test.txt”)
objFile.Write(“text1”)
objFile.Write(“text2”)
objFile.Write(“text3”)
objFile.Close()
This snippet produces a text file that contains the following:
text1text2text3
See how WriteLine() creates lines of data, whereas Write() simply streams the data
into the file? This is an incredibly important distinction, and understanding the difference
is crucial to your success with writing text files. Which method you choose
depends on what you are trying to accomplish. I think perhaps WriteLine() is the
more common way. The following code illustrates how you could use WriteLine() to
store a list of albums (assuming that you have the list in a list box titled lstAlbums):
Dim objFile As New System.IO.StreamWriter(“c:\albums.txt”)
Dim intCounter As Long = lstAlbums.Items.Count
For intCounter = 0 To lstAlbums.Items.Count - 1
objFile.WriteLine(lstAlbums.Items(intCounter).ToString)
Next intCounter
objFile.Close()
Reading a Text File
Reading a text file is handled by the StreamReader class, which behaves similarly to the
StreamWriter class. First, you need to define an object of type StreamReader, like this:
Dim objFile As New System.IO.StreamReader(“c:\test.txt”)
A key difference in declaring a StreamReader object versus a StreamWriter object is
how the code behaves if the file is not found. The StreamWriter object is happy to
create a new text file for you if the specified file isn’t found. If StreamReader can’t
find the specified file, it throws an exception—something you need to account for in
your code.
Just as StreamWriter lets you write the data to the file in one of seven ways,
StreamReader also has multiple ways to read the data. The first of the two most common
ways is to use the ReadToEnd() method, which reads the entire file and is used
to place the contents of the file into a variable. You would use ReadToEnd() like this:
Dim objFile As New System.IO.StreamReader(“c:\test5.txt”)
Dim strContents As String
strContents = objFile.ReadToEnd()
objFile.Close()
objFile.Dispose()
MessageBox.Show(strContents)
442 HOUR 20: Working with the Registry and Text Files
The ReadToEnd() method can be handy, but sometimes you just want to get a single
line of text at a time. For example, consider the text file created by the previous
example, the one with a list of albums. Say that you wanted to read the text file and
place all the albums found in the text file into a list box named lstAlbums. The
ReadToEnd() method would allow you to get the data, but then you would have to
find a way to parse each album name. The proper solution for reading one line at a
time is to use the ReadLine() method. The following code shows how you could load
the Albums.txt text file, one line at a time, and place each album name in a list box:
Dim objFile As New System.IO.StreamReader(“c:\albums.txt”)
Dim strAlbumName As String
strAlbumName = objFile.ReadLine()
Do Until strAlbumName Is Nothing
lstAlbums.Items.Add(strAlbumName)
strAlbumName = objFile.ReadLine()
Loop
objFile.Close()
objFile.Dispose()
A couple of important concepts in this example need discussing. The first is how you
know when you’ve reached the end of a text file. The answer is that the return result
will be Nothing. So, the first thing this code does (after creating the StreamReader
object and the String variable) is get the first line from the text file. It’s possible that
the text file could be empty, so the Do loop tests for this. If the string is Nothing, the
file is empty, so the loop doesn’t execute. If the string is not Nothing, the loop begins.
The first statement in the loop adds the string to the list box. The next statement gets
the next line from the file. This sends execution back to the Do statement, which
again tests to see whether we’re at the end of the file. One thing this code doesn’t test
for is a zero-length string (””). If the text file has a blank line, the string variable
holds a zero-length string. You might want to test for a situation like this when working
with text files in your code.
That’s it! Text files are not database files; you’ll never get the power and flexibility
from a text file that you would from a real database. With that said, text files are
easy to work with and provide amazing and quick results within the context of their
design.
Modifying Your Picture Viewer Project to Use a
Text File
In this section, you’ll modify your Picture Viewer project to use a text file. You’ll have
your Picture Viewer update a log (a text file) every time the user views a picture.
You’ll then create a simple dialog box that the user can open to view the log file. If
you no longer have the Picture Viewer project open from earlier, open it now.
Reading and Writing Text Files 443
Creating the Picture Viewer Log File
In this section, you’ll modify the Picture Viewer project to create the log file. Follow
these steps to implement the log functionality:
1. Double-click ViewerForm.vb in the Solution Explorer window to display the
form in the designer.
2. Recall that you created a single procedure that is called from both the menu
and the toolbar to open a picture. This makes it easier, because you have to add
the log code in only one place. Double-click the Open Picture button on the
toolbar to access its Click event.
3. You now need to go to the OpenPicture() function. Here’s an easy way to do
this: Right-click the code OpenPicture(), and choose Go To Definition from the
shortcut menu, as shown in Figure 20.5. Whenever you do this to a procedure
call, Visual Basic displays the code of the procedure being referenced.
4. Take a look at the OpenPicture() procedure. Where would you place the code
to create a log file? Would you enter all the log file code right into this procedure?
First, the log file should be updated only when a picture is successfully
loaded, which would be in the Try block, right after the statement that updates
the sbrMyStatusStrip control. Second, the log code should be isolated from
FIGURE 20.5
Go To Definition
is a quick way to
view a procedure
being called in
code.
444 HOUR 20: Working with the Registry and Text Files
FIGURE 20.6
It’s always a
good idea to isolate
code into
cohesive procedures.
this procedure, so you’ll add just a single function call. Add this statement
between the code to update the status bar and the End If:
UpdateLog(ViewerForm.ofdSelectPicture.FileName)
Your code should look like Figure 20.6. Note that it currently has an error (the
procedure UpdateLog doesn’t exist), but you’re about to correct that.
5. Position the cursor between the End Sub of OpenPicture() and the declaration
of the DrawBorder() procedure. Press Enter to create a new line, and then enter
the following procedure code:
Private Sub UpdateLog(ByVal strFileName As String)
Dim objFile As New System.IO.StreamWriter( _
System.AppDomain.CurrentDomain.BaseDirectory() & “\PictureLog.txt”, _
True)
objFile.WriteLine(Today() & “ “ & strFileName)
objFile.Close()
objFile.Dispose()
End Sub
Most of this code should be recognizable, but consider this snippet:
System.AppDomain.CurrentDomain.BaseDirectory() & “\PictureLog.txt”
The method BaseDirectory() returns the path of the running program. This is a
great trick to know! What you’ve done here is append the filename PictureLog.txt to
Reading and Writing Text Files 445
By the
Way
the application path so that the log file is always created in the application path.
This makes it easy for the user to find the log file. In a robust application, you might
let the user specify a path, perhaps storing it in the Registry. For our purposes, the
application path works just fine.
When you’re debugging an application in the Visual Basic IDE, the application path
might not be exactly what you expect. When you compile and test your application,
Visual Basic creates a bin\Debug folder under the folder containing your project.
This is where it places the temporary .exe file it creates for debugging, and this is
your application path. If you go looking for the log file in your project folder, you
won’t find it. You need to drill down into the \bin\Debug folder to get it.
Displaying the Picture Viewer Log File
In this section, you’ll modify the Picture Viewer project to include a dialog box that
the user can display to view the log file. Follow these steps to implement the log
viewer functionality:
1. Choose Project, Add Windows Form to display the Add New Item dialog box.
Enter LogViewerForm.vb as the new form name, and click Add to create the
form.
2. Set the properties of the new form as follows:
3. Add a new button to the form, and set its properties as follows:
4. Add a new text box to the form, and set its properties as follows:
Property Value
MaximizeBox False
MinimizeBox False
Size 520, 344
Text Picture Viewer History Log
Property Value
Name btnOK
Anchor Top, Right
Location 425, 275
Text OK
Property Value
Name txtLog
Anchor Top, Bottom, Left, Right
446 HOUR 20: Working with the Registry and Text Files
Property Value
Name tbbShowLog
Image Log.png (found with the samples on my website)
Location 3, 12
Multiline True
ReadOnly True
Size 497, 257
5. Double-click the OK button to access its Click event, and enter the following
statement:
Me.Close()
6. Add the code that actually displays the log. Choose (LogViewerForm Events)
from the object drop-down list in the upper-left corner of the code window.
Then choose Load from the Event drop-down list in the upper right of the code
window. Enter the following code into the Form_Load event:
Try
Dim objFile As New System.IO.StreamReader( _
System.AppDomain.CurrentDomain.BaseDirectory() & _
“\PictureLog.txt”)
txtLog.Text = objFile.ReadToEnd()
objFile.Close()
objFile.Dispose()
Catch ex As Exception
txtLog.Text = “The log file could not be found.”
End Try
This code is just like the code discussed earlier on reading text files. It uses
ReadToEnd() to load the entire log into the text box. The whole thing is
wrapped in a Try...End Try block to handle the situation of there being no
log file.
7. All that’s left is to add a button to the toolbar of the Picture Viewer to display
the log. Double-click ViewerForm.vb in the Solution Explorer to display the
form in the designer.
8. Click the Toolstrip to select it, and then click the Items property in the Properties
window.
9. Click the Build button in the Items property in the Property window to access
the Items Collection Editor, and then create a new button on the toolbar. Set
the new button’s properties as follows:
Reading and Writing Text Files 447
10. Click OK to save the new button; then double-click the new button on the toolbar
and add the following code:
LogViewerForm.ShowDialog()
Testing Your Picture Viewer Log
Save your project, and press F5 to run it. Follow these steps to test the project:
1. Click the View Picture Log button on the toolbar to display the Picture Viewer
History Log. Notice that the text box displays The log file could not be
found. This means the Try block worked!
2. Click OK to close the form.
3. Click the Open Picture button on the toolbar, browse to a picture file, and display
it.
4. Click the View Picture Log button again. Notice that the log now displays a log
entry, as shown in Figure 20.7.
Property Value
Text View Picture Log
ToolTipText View Picture Log
FIGURE 20.7
Text files make
creating logs
easy.
448 HOUR 20: Working with the Registry and Text Files
Summary
In this hour, you learned how to use the Registry to store and retrieve user settings.
You learned about the structure of the Registry and how to use hives, keys, and values.
The Registry is a powerful tool, and you should use it when applicable. Remember:
The Registry isn’t your personal repository; respect the Registry! Windows relies
on certain data in the Registry, and if you mess up the Registry, you can actually prevent
a computer from booting to Windows. As you saw firsthand with the Picture
Viewer project, saving data to and retrieving data from the Registry is relatively easy,
but how you handle the data is the real trick.
Next, you learned about the power (and limitations) of working with text files. You
can read and write text files, but you can’t do both to a single text file at the same
time. If you need that functionality, a database is the way to go. However, you
learned that it’s relatively easy to store and retrieve sequential information in a text
file, such as a log file. Finally, you used what you learned to implement log functionality
for the Picture Viewer project.
Q&A
Q. Can I use a text file to save configuration information?
A. Yes, you could do that. You would need some way to denote the data element.
How would you know that the first line was the BackColor setting, as opposed
to a default file path, for example? One method would be to append the data
element to a caption, as in BackColor=White. You would then have to parse
the data as you read it from the text file. The Registry is probably a better solution
for something like this, but a text file could be useful if you wanted to
transfer settings to a different computer.
Q. Can I store binary data instead of text to a file?
A. Visual Basic includes classes designed to work with binary files: BinaryWriter
and BinaryReader. You would need to use objects based on these classes,
instead of using StreamWriter and StreamReader objects.
Workshop 449
Workshop
Quiz
1. Why should you use the Registry object instead of the built-in Visual Basic
functions to work with the Registry?
2. Under what hive should you store a user’s configuration information in the
Registry?
3. What full object/method is used to create a key in the Registry?
4. What two methods are used to delete a key from the Registry, and what is the
difference between the two?
5. What classes do you use to write and read text files?
6. What method of the StreamReader class do you use to read the entire contents
of a text file at once?
7. What happens if you attempt to use the StreamReader class to open a file that
doesn’t exist?
Answers
1. The built-in functions restrict you to working with keys and values under specific
Visual Basic keys only.
2. You should store user configuration in the HKEY_CURRENT_USER hive.
3. My.Computer.Registry.CurrentUser.CreateSubKey()
4. The method DeleteSubKey() deletes a key, but only if no subkeys exist for the
specified key. The method DeleteSubKeyTree() deletes a key and any subkeys
of the specified key.
5. The StreamWriter class is used to write to a text file, whereas the
StreamReader class is used to read data from a text file.
6. The ReadToEnd() method
7. An exception is thrown.
450
Exercises
1. Every toolbar item should have a corresponding menu item. Create a menu
item on the Tools menu for displaying the log. While you’re at it, create one for
viewing the file properties to match the toolbar item you created in Hour 19.
(You should move the code in tbbGetFileAttributes_Click to its own procedure
so that it can be called from both the menu and the toolbar.) Finally, go
back and add images to your menu items so that they match the toolbar items.
2. Create a button on the Log Viewer form called btnClearLog. Change the text
of the button to Clear. When the user clicks the button, delete the log file from
the hard drive and close the Log Viewer form.
HOUR 20: Working with the Registry and Text Files
451
HOUR 21
Working with a Database
What You’ll Learn in This Hour:
. Introduction to ADO.NET
. Connecting to a database
. Understanding DataTables
. Creating a DataAdapter
. Referencing fields in a DataRow
. Navigating records
. Adding, editing, and deleting records
. Building an ADO.NET example
You’ve heard it so many times that it’s almost a cliché: This is the Information Age.
Information is data, and managing information means working with databases.
Database design is a skill unto itself, and entire books are devoted to database design
and management. In this hour, you’ll learn the basics of working with a database
using ADO.NET, Microsoft’s newest database technology. High-end solutions are built
around advanced database technologies such as Microsoft’s SQL Server, which is the
database technology used in this chapter. If you don’t have Microsoft SQL Server
2008 installed on your computer, you can download it at http://www.microsoft.com/
express/sql/default.aspx; you have to have Microsoft SQL Server 2008 installed for
the code in this chapter to work.
452 HOUR 21: Working with a Database
By the
Way You’ll learn a lot in this hour, but realize that this material is really the tip of the
iceberg. Database programming is often complex. This hour is intended to get you
writing database code as quickly as possible, but if you plan to do a lot of database
programming, you’ll want to consult a book (or two) dedicated to the subject.
Begin by creating a new Windows Application named Database Example. Right-click
Form1.vb in the Solution Explorer window, choose Rename, and then change the
name of the default form to MainForm.vb. Next, set the form’s Text property to
Database Example.
Now that the project has been created, follow the steps in the next sections to build
your database project.
Introducing ADO.NET
ADO.NET is the .NET platform’s database technology, and it builds on the older ADO
(Active Data Objects) technology. ADO.NET provides DataSet and DataTable objects
that are optimized for moving disconnected sets of data across the Internet and
intranets, including through firewalls. At the same time, ADO.NET includes the traditional
connection and command objects, as well as an object called a DataReader
(which resembles a forward-only, read-only ADO RecordSet, in case you’re familiar
with ADO). Together, these objects provide the best performance and throughput for
retrieving data from a database.
In short, you’ll learn about the following objects as you progress through this hour:
. SqlConnection is used to establish a connection to a SQL Server data source.
. DataSet is a memory-resident representation of data. There are many ways of
working with a DataSet, such as through DataTables.
. DataTable holds a result set of data for manipulation and navigation.
. DataAdapter is used to populate a DataReader.
All the ADO.NET objects, except the DataTable, are part of the System.Data namespace.
The DataTable is part of System.Xml. Follow these steps to add references to
both namespaces so that you can use the namespaces without having to type the full
namespace qualifier:
1. Choose Project, Database Example Properties to display the Project Properties.
2. Click the References tab to display the active references for the project, as
shown in Figure 21.1.
Introducing ADO.NET 453
FIGURE 21.1
You use Project
Properties to
import namespaces.
3. In the lower part of this page is a check box list of imported namespaces. Use
the scrollbar for this list box (not the main scrollbar for the page) to locate and
check System.Data, System.Data.SqlClient, and System.Xml. System.Data
is probably already checked and will appear toward the top of the list. If not,
locate it and check it. System.Data.SqlClient and System.Xml will most
likely not be checked, and will be toward the bottom of the list.
4. Click Save All on the toolbar.
5. Click MainForm.vb [Design] to return to the Form Designer.
Connecting to a Database
To access data in a database, you must first establish a connection, using an
ADO.NET connection object. Multiple connection objects are included in the .NET
Framework, such as the OleDbConnection object (for working with the same OLE DB
data providers you would access through traditional ADO) and the SqlConnection
object (for optimized access to Microsoft SQL Server). Because these examples connect
to a Microsoft SQL Database, you’ll be using the SqlConnection object. To create an
object variable of type SqlConnection and initialize the variable to a new connection,
you could use a statement like this:
454 HOUR 21: Working with a Database
TABLE 21.1 Possible Parameters for ConnectionString
Parameter Description
Provider The name of the data provider (Jet, SQL,
and so on) to use.
Data Source The name of the data source (database) to
connect to.
User ID A valid username to use when connecting
to the data source.
Password A password to use when connecting to the
data source.
DRIVER The name of the database driver to use.
This isn’t required if a data source name
(DSN) is specified.
SERVER The network name of the data source
server.
Dim cnADONetConnection As New SQLConnection()
You’ll create a module-level variable to hold the connection. Double-click the form
now to access its events, and place the cursor below the class definition statement at
the top of the module. Enter the following statement:
Private m_cn As New SQLConnection()
Before using this connection, you must specify the data source to which you want to
connect. This is done through the ConnectionString property of the ADO.NET connection
object. The ConnectionString contains connection information such as the
name of the provider, username, and password. The ConnectionString might contain
many connection parameters; the set of parameters available varies, depending
on the source of data to which you’re connecting. Table 21.1 lists some of the parameters
used in the SQL ConnectionString. If you specify multiple parameters, separate
them with a semicolon.
The Provider= parameter is one of the most important at this point; it is governed by
the type of database you’re accessing. For example, when accessing a SQL Server
database, you specify the provider information for SQL Server, and when accessing a
Jet database, you specify the provider for Jet. In this example, you access a Microsoft
SQL database, so you use the provider information for Microsoft SQL.
Introducing ADO.NET 455
By the
Way
In addition to specifying the provider, you also need to specify the database. I’ve provided
a sample database on this book’s website. This code assumes that you’ve placed
the database in a folder called C:\Temp. If you’re using a different folder, you need to
change the code accordingly. Follow these steps:
1. Specify the ConnectionString property of your ADO.NET connection by placing
the following statement in your form’s Load event:
m_cn.ConnectionString = “Data Source=.\SQLEXPRESS; AttachDbFilename = “ & _
“C:\Temp\Test.mdf;Integrated Security=True; Connect Timeout=30;” & _
“User Instance=True”
2. After the connection string is defined, you establish a connection to a data
source by using the Open() method of the connection object. Add the following
statement to the Load event, right after the statement that sets the connection
string:
m_cn.Open()
Refer to the online documentation for information on connection strings for
providers other than Microsoft SQL Server.
When you attach to an unsecured Microsoft SQL Server database, it isn’t necessary to
provide a username and password. When attaching to a secured database, however,
you must provide a username and a password. You do so by passing the username
and password as parameters in the ConnectionString property. The sample database
I’ve provided isn’t secured, so you don’t need to provide a username and password.
Closing a Connection to a Data Source
You close a connection to a data source. That means you shouldn’t rely on a variable
going out of scope to close a connection. Instead, you should force an explicit disconnect
via code. You do so by calling the Close() method of the connection object.
Now you’ll write code to explicitly close the connection when the form is closed.
Start by opening the object drop-down list in the code window and selecting Main-
Form Events if it isn’t already selected. Next, choose FormClosed from the event dropdown
list to create an event handler for the FormClosed event. Enter the following
statements in the FormClosed event:
m_cn.Close()
m_cn.Dispose()
456 HOUR 21: Working with a Database
Manipulating Data
The easiest way to manipulate data when using ADO.NET is to create a DataTable
object containing the result set of a table, query, or stored procedure. Using a
DataTable object, you can add, edit, delete, find, and navigate records. The following
sections explain how to use DataTables.
Understanding DataTables
DataTables contain a snapshot of data in the data source. You generally start by filling
a DataTable, manipulating its results, and finally sending the changes back to
the data source. You populate the DataTable by using the Fill() method of a
DataAdapter object, and changes are sent back to the database through use of the
Update() method of a SqlDataAdapter. Any changes made to the DataTable
appear only in the local copy of the data until you call the Update method. Having a
local copy of the data reduces contention by preventing users from blocking others
from reading the data while it’s being viewed. If you’re familiar with ADO, you’ll
note that this is similar to the Optimistic Batch Client Cursor in ADO.
Creating a DataAdapter
To populate a DataTable, you must create a SqlDataAdapter. The DataAdapter
you’ll create uses the connection you’ve already defined to connect to the data source
and then executes a query you provide. The results of that query are pushed into a
DataTable.
As mentioned earlier, the .NET Framework has multiple connection objects. It has
multiple ADO.NET DataAdapter objects as well. You’ll use the SqlDataAdapter
because you will be connecting to Microsoft SQL Server.
The constructor for an SqlDataAdapter optionally takes the command to execute
when filling a DataTable or DataSet, as well as a connection specifying the data
source (you could have multiple connections open in a single project). This constructor
has the following syntax:
Dim daSqlDataAdapter As New SqlDataAdapter([CommandText],[Connection])
To add an SqlDataAdapter to your project, follow these steps:
1. Add the following statement immediately below the statement you entered to
declare the m_cn object (in the class header, not in the Load event) to create a
module-level variable:
Private m_DA As SqlDataAdapter
Manipulating Data 457
2. Add the following statement at the bottom of the form’s Load event (immediately
following the statement that opens the connection):
m_DA = New SqlDataAdapter(“Select * From Contacts”, m_cn)
Because you’ll use the SqlDataAdapter to update the original data source, you
must specify the insert, update, and delete statements to use to submit changes
from the DataTable to the data source. ADO.NET lets you customize how
updates are submitted by enabling you to manually specify these statements as
database commands or stored procedures. In this case, you’ll have ADO.NET
generate these statements automatically by creating a CommandBuilder object.
3. Enter this statement in the class header to create the CommandBuilder modulelevel
variable:
Private m_CB As SqlCommandBuilder
The CommandBuilder is an interesting object in that after you initialize it, you
no longer work with it directly. It works behind the scenes to handle the updating,
inserting, and deleting of data. To make this work, you have to attach the
CommandBuilder to a SqlDataAdapter. You do so by passing a
SqlDataAdapter to the CommandBuilder. The CommandBuilder then registers
for update events on the SqlDataAdapter and provides the insert, update, and
delete commands as needed.
4. Add the following statement to the end of the Form_Load event to initialize the
CommandBuilder object:
m_CB = New SqlCommandBuilder(m_DA)
Your code should now look like Figure 21.2.
FIGURE 21.2
You jump around
a lot in this
example. Be
sure to follow
the steps
exactly!
458 HOUR 21: Working with a Database
FIGURE 21.3
This code
accesses a database
and creates
a
DataTable that
can be used anywhere
in the
class.
Creating and Populating DataTables
You need to create a module-level DataTable in your project. Follow these steps:
1. Create the DataTable variable by adding the following statement on the class
header to create another module-level variable:
Private m_DataTable As New DataTable
2. You use an integer variable to keep track of the user’s current position (row)
within the DataTable. To do this, add the following statement immediately
below the statement you just entered to declare the new DataTable object:
Private m_rowPosition As Integer = 0
3. You now have a SqlDataAdapter that allows access to a data source via the
connection. You’ve declared a DataTable that will hold a reference to data.
Next, add the following statement to the form’s Load event, after the existing
code, to fill the DataTable with data:
m_DA.Fill(m_DataTable)
Because the DataTable doesn’t hold a connection to the data source, you don’t need
to close it when you’re finished. Your class should now look like the one shown in
Figure 21.3.
Manipulating Data 459
By the
Way
Referencing Fields in a DataRow
DataTables contain a collection of DataRows. To access a row within the DataTable,
you specify the ordinal (index) of that DataRow. For example, you could access the
first row of your DataTable like this:
Dim m_DataRow As DataRow = m_DataTable.Rows(0)
Data elements in a DataRow are called columns. For example, the Contacts table I’ve
created has two columns: ContactName and State. To reference the value of a column,
you can pass the column name to the DataRow like this:
’ Change the value of the column.
m_DataRow(“ContactName”) = “Bob Brown”
or
’ Get the value of the column.
strContactName = m_DataRow (“ContactName”)
If you misspell a column name, an exception occurs when the statement executes
at runtime; no errors are raised at compile time.
Now you create a procedure that’s used to display the current record in the data
table. Follow these steps:
1. Position the cursor after the End Sub for the MainForm_FormClosed event (after
its End Sub statement), and press Enter a few times to create some blank lines.
2. Enter the following procedure in its entirety:
Private Sub ShowCurrentRecord()
If m_DataTable.Rows.Count = 0 Then
txtContactName.Text = ““
txtState.Text = ““
Exit Sub
End If
txtContactName.Text = _
m_DataTable.Rows(m_rowPosition)(“ContactName”).ToString()
txtState.Text = _
m_DataTable.Rows(m_rowPosition)(“State”).ToString()
End Sub
460 HOUR 21: Working with a Database
Property Value
Name txtState
Location 168, 112
Size 80, 20
Property Value
Name txtContactName
Location 48, 112
Size 112, 20
FIGURE 21.4
It takes quite a
bit of prep work
to display data
from a
database.
3. Make sure that the first record is shown when the form loads by adding this
statement to the Form_Load event, after the existing statements:
Me.ShowCurrentRecord()
You’ve now ensured that the first record in the DataTable is shown when the
form first loads. To display the data, you must add a few controls to the form.
4. Create a new text box, and set its properties as follows:
5. Add a second text box to the form, and set its properties according to the following
table:
6. Press F5 to run the project. The first contact in the Contacts table is displayed in
the text box, as shown in Figure 21.4.
Navigating Records
The ADO.NET DataTable object supports a number of methods that can be used to
access its DataRows. The simplest of these is the ordinal accessor that you used in
Manipulating Data 461
your ShowCurrentRecord() method. Because the DataTable has no dependency on
the source of the data, this same functionality is available regardless of where the
data comes from.
Now you need to create buttons that the user can click to navigate the DataTable.
The first button is used to move to the first record in the DataTable. Follow these steps:
1. Stop the running project and display the Form Designer for MainForm.vb.
2. Add a new button to the form, and set its properties as follows:
3. Double-click the button, and add the following code to its Click event:
’ Move to the first row and show the data.
m_rowPosition = 0
Me.ShowCurrentRecord()
4. A second button is used to move to the previous record in the DataTable. Add
another button to the form, and set its properties as shown in the following table:
Property Value
Name btnMoveFirst
Location 12, 152
Size 32, 23
Text <<
Property Value
Name btnMoveNext
Location 86, 152
5. Double-click the button, and add the following code to its Click event:
’ If not at the first row, go back one row and show the record.
If m_rowPosition > 0 Then
m_rowPosition = m_rowPosition - 1
Me.ShowCurrentRecord()
End If
6. A third button is used to move to the next record in the DataTable. Add a third
button to the form, and set its properties as shown in the following table:
Property Value
Name btnMovePrevious
Location 48, 152
Size 32, 23
Text <
462 HOUR 21: Working with a Database
Property Value
Name btnMoveLast
Location 124, 152
Size 32, 23
Text >>
Size 32, 23
Text >
Property Value
Name btnSave
Location 162, 152
7. Double-click the button, and add the following code to its Click event:
’ If not on the last row, advance one row and show the record.
If m_rowPosition < (m_DataTable.Rows.Count - 1) Then
m_rowPosition = m_rowPosition + 1
Me.ShowCurrentRecord()
End If
8. A fourth button is used to move to the last record in the DataTable. Add yet
another button to the form, and set its properties as shown in the following table:
9. Double-click the button, and add the following code to its Click event:
’ If there are any rows in the data table, move to the last and show
‘ the record.
If m_DataTable.Rows.Count > 0 Then
m_rowPosition = m_DataTable.Rows.Count - 1
Me.ShowCurrentRecord()
End If
Editing Records
To edit records in a DataTable, you change the value of a particular column in the
desired DataRow. Remember, though, that changes aren’t made to the original data
source until you call Update() on the SqlDataAdapter, passing in the DataTable
containing the changes.
Now it’s time to add a button that the user can click to update the current record. Follow
these steps:
1. Add a new button to the form, and set its properties as follows:
Workshop 463
2. Double-click the Save button, and add the following code to its Click event:
’ If there is existing data, update it.
If m_DataTable.Rows.Count <> 0 Then
m_DataTable.Rows(m_rowPosition)(“ContactName”) = txtContactName.Text
m_DataTable.Rows(m_rowPosition)(“State”) = txtState.Text
m_DA.Update(m_DataTable)
End If
Creating New Records
You add records to a DataTable much as you edit records. However, to create a new
row in the DataTable, you must first call the NewRow() method. After creating the
new row, you can set its column values. The row isn’t actually added to the
DataTable, however, until you call the Add() method on the DataTable’s
RowCollection.
Now you need to modify your interface so that the user can add new records. One
text box is used for the contact name and a second text box for the state. When the
user clicks the button you provide, the values in these text boxes are written to the
Contacts table as a new record. Follow these steps:
1. Start by adding a group box to the form and setting its properties as shown in
the following table:
2. Add a new text box to the group box (not to the form), and set its properties as
follows:
Size 40, 23
Text Save
Property Value
Name grpNewRecord
Location 16, 192
Size 256, 58
Text New Contact
Property Value
Name txtNewContactName
Location 8, 24
Size 112, 20
464 HOUR 21: Working with a Database
Property Value
Name txtNewState
Location 126, 24
Size 80, 20
Property Value
Name btnAddNew
Location 210, 22
Size 40, 23
Text Add
Property Value
Name btnDelete
Location 208, 152
Size 56, 23
Text Delete
3. Add a second text box to the group box, and set its properties as shown:
4. Finally, add a button to the group box, and set its properties as follows:
5. Double-click the Add button, and add the following code to its Click event:
Dim drNewRow As DataRow = m_DataTable.NewRow()
drNewRow(“ContactName”) = txtNewContactName.Text
drNewRow(“State”) = txtNewState.Text
m_DataTable.Rows.Add(drNewRow)
m_DA.Update(m_DataTable)
m_rowPosition = m_DataTable.Rows.Count - 1
Me.ShowCurrentRecord()
Notice that after the new record is added, the position is set to the last row, and the
ShowCurrentRecord() procedure is called. This causes the new record to appear in
the display text boxes you created earlier.
Deleting Records
To delete a record from a DataTable, you call the Delete() method on the DataRow
to be deleted. Follow these steps:
1. Add a new button to your form (not to the group box), and set its properties as
shown in the following table:
Manipulating Data 465
2. Double-click the Delete button, and add the following code to its Click event:
’ If there is data, delete the current row.
If m_DataTable.Rows.Count <> 0 Then
m_DataTable.Rows(m_rowPosition).Delete()
m_DA.Update(m_DataTable)
m_rowPosition = 0
Me.ShowCurrentRecord()
End If
Your form should now look like the one shown in Figure 21.5.
Running the Database Example
Press F5 to run the project. If you entered all the code correctly and you placed the
Contacts database in the C:\Temp folder (or modified the path used in code), the
form should be displayed without errors, and the first record in the database appears.
Click the navigation buttons to move forward and backward. Feel free to change a
contact’s information; click the Save button, and your changes are made to the
underlying database. Next, enter your name and state into the New Contact section
of the form, and click Add. Your name is then added to the database and displayed
in the appropriate text boxes.
FIGURE 21.5
A basic dataentry
form.
466 HOUR 21: Working with a Database
Summary
Most commercial applications use some sort of database. Becoming a good database
programmer requires extending your skills beyond just being a good Windows programmer.
There’s so much to know about optimizing databases and database code,
creating usable database interfaces, creating a database schema—the list goes on.
Writing any database application, however, begins with the basic skills you learned
in this hour. You learned how to connect to a database, create and populate a
DataTable, and navigate the records in the DataTable. In addition, you learned how
to edit records and how to add and delete records. Although this just scratches the
surface of database programming, it is all you need to begin writing your own small
database application.
Q&A
Q. If I want to connect to a data source other than Microsoft SQL Server, how
do I know what connection string to use?
A. Different connection information is available not only for different types of
data sources but also for different versions of different data sources. The best
way to determine the connection string is to consult the documentation for the
data source to which you want to attach.
Q. What if I don’t know where the database will be at runtime?
A. For file-based data sources such as Jet or Microsoft SQL Server, you can add an
Open File Dialog control to the form and let the user browse and select the
database. Then concatenate the filename with the rest of the connection information
(such as the provider string).
Workshop
Quiz
1. What is the name of the data access namespace used in the .NET Framework?
2. What is the name given to a collection of DataRows?
3. How do you get data into and out of a DataTable of a Microsoft SQL Server
database?
Workshop 467
4. What object is used to connect to a data source?
5. What argument of a connection string contains information about the type of
data being connected to?
6. What object provides update, delete, and insert capabilities to a DataAdapter?
7. What method of a DataTable object do you call to create a new row?
Answers
1. System.Data
2. A DataSet
3. You use a SqlDataAdapter.
4. There are multiple connection objects. You have to use the connection object
appropriate for the type of data you are accessing.
5. The Provider argument
6. A CommandBuilder object
7. The Add() method is used to create the row. The Update() method saves your
changes to the new row.
Exercises
1. Create a new project that connects to the same database used in this example.
Rather than displaying a single record in two text boxes, put a list box on the
form, and fill the list box with the names of the people in the database.
2. Right now, the code you created in this hour saves an empty name to the database.
Add code to the Click event of the Add button so that it first tests to see
whether the user entered a contact name. If not, tell the user that a name is
required, and then exit the procedure.
This page intentionally left blank
469
HOUR 22
Controlling Other
Applications Using
Automation
What You’ll Learn in This Hour:
. Creating a reference to an automation library
. Creating an instance of an automation server
. Manipulating the objects of an automation server
. Automating Microsoft Word
. Automating Microsoft Excel
In Hour 16, “Designing Objects Using Classes,” you learned how to use classes to create
objects. In that hour, I mentioned that objects could be exposed to outside applications.
Excel, for example, exposes most of its functionality as a set of objects. The
process of using objects from another application is called automation. The externally
accessible objects of an application comprise its object model. Using automation to
manipulate a program’s object model enables you to reuse components. For example,
you can use automation with Excel to perform complex mathematical functions,
using the code that’s been written and tested within Excel rather than writing and
debugging the complex code yourself.
Programs that expose objects are called servers, and programs that consume objects
are called clients. Creating automation servers requires advanced skills, including a
thorough understanding of programming classes. On the other hand, creating clients
to use objects from other applications is relatively simple. In this hour, you’ll learn
how to create a client application that uses objects of an external server application.
To understand automation, you’ll build two projects. The first is a Microsoft Excel
client—a program that automates Excel via Excel’s object model. The second project
automates Microsoft Word.
470 HOUR 22: Controlling Other Applications Using Automation
By the
Way
Property Value
Name btnAutomateExcel
Location 90, 128
Size 104, 23
Text Automate Excel
These exercises are designed to work with Microsoft Excel 2007 and Microsoft
Word 2007. You must have these programs installed for the examples to work.
Automating Microsoft Excel
Begin by creating a new Windows Application named Automate Excel. Right-click
Form1.vb in the Solution Explorer, choose Rename, and then change the name of the
default form to MainForm.vb. Next, set the form’s Text property to Automate Excel.
Add a button to the form by double-clicking the Button item in the toolbox, and set
the button’s properties as follows:
Creating a Reference to an Automation Library
To use the objects of a program that supports automation (a server), you have to reference
the program’s type library. A program’s type library (also called its object library)
is a file containing a description of the program’s object model. After you’ve referenced
the type library of an automation server (also called a component), you can
access the server’s objects as though they were internal Visual Basic objects.
You create the reference to Excel’s automation library much as you created a reference
to the System.Data namespace in Hour 21, “Working with a Database.” To create
a reference to the Excel library, follow these steps:
1. Choose Project, Automate Excel Properties to display the Project Properties.
2. Click the References tab to display the active references for the project, as
shown in Figure 22.1.
3. Below the list of existing references (and above the imported namespaces), click
the Add button to display the list of available references.
4. On the COM tab, shown in Figure 22.2, locate Microsoft Excel 12.0 Object
Library and double-click it. This selects the library and closes the Add Reference
dialog box. The COM reference appears in the References list in the Project
Properties window.
Automating Microsoft Excel 471
By the
Way
FIGURE 22.1
You use Project
Properties to
add references
to COM servers.
FIGURE 22.2
You have to add
a reference to
the Excel library
before you can
use it in code.
If you don’t see Microsoft Excel 12.0 Object Library in your list of available COM
references, you probably don’t have Excel 2007 installed, and this example will
not work.
5. In the lower part of the References page is a check box list of imported namespaces.
Use the scrollbar for this list box (not the main scrollbar for the page) to
472 HOUR 22: Controlling Other Applications Using Automation
By the
Way
By the
Way
locate and check Microsoft.Office.Interop. This most likely is one of the last
items in the list.
6. Click Save All on the toolbar.
7. Click MainForm.vb [Design] to return to the Form Designer.
Visual Basic doesn’t work directly with COM components (as did previous versions
of Visual Basic). Instead, it interacts through a wrapper, a set of code and
objects that works as an intermediary between Visual Basic and a COM component.
When you add the reference to a COM component, .NET automatically creates
this wrapper for you.
Creating an Instance of an Automation Server
Referencing a type library enables Visual Basic to integrate the available objects of
the type library with its own internal objects. After this is done, you can create object
variables based on object types found in the type library. Excel has an object called
Application, which acts as the primary object in the Excel object model. In fact,
most Office programs have an Application object. How do you know what objects
an automation server supports? The only sure way is to consult the documentation of
the program in question or use the Object Browser, as discussed in Hour 3, “Understanding
Objects and Collections.”
This example uses about a half-dozen members of an Excel object. This doesn’t
even begin to scratch the surface of Excel’s object model, nor is it intended to.
What you should learn from this example is the mechanics of working with an
automation server. If you choose to automate a program in your own projects,
consult the program’s developer documentation to learn as much about its object
model as you can. You’re sure to be surprised at the functionality available to you.
Double-click the button to access its Click event, and then enter the following code,
which creates a new Excel Application object:
Dim objExcel As New Excel.Application
Notice that Visual Basic includes Excel in its IntelliSense drop-down list of available
objects. It can do this because you referenced Excel’s type library. Excel is the reference
to the server, and Application is an object supported by the server. This statement
creates a new Application object based on the Excel object model.
Automating Microsoft Excel 473
Manipulating the Server
After you have an instance of an object from an automation server, you manipulate
the server (create objects, set properties, call methods, and so forth) by manipulating
the object. In the following sections, you manipulate the new Excel object by setting
properties and calling methods, and in so doing you manipulate Excel itself.
Forcing Excel to Show Itself
When you use automation to start Excel, it’s loaded hidden—the user can’t see the
user interface. By remaining hidden, Excel allows the developer to use Excel’s functionality
and then close it without the user even knowing what happened. For example,
you could create an instance of an Excel object, perform a complicated formula
to obtain a result, close Excel, and return the result to the user—all without the user
seeing Excel. In this example, you want to see Excel so that you can see what your
code is doing. Fortunately, showing Excel couldn’t be any easier. Add the following
statement to make Excel visible:
ObjExcel.Visible = True
Creating an Excel Workbook
In Excel, a workbook is the file in which you work and store your data; you can’t
manipulate data without a workbook. When you first start Excel from the Start
menu, an empty workbook is created. When you start Excel via automation, however,
Excel doesn’t create a workbook; you have to do it yourself. To create a new workbook,
you use the Add method of the Workbooks collection. Enter the following statement
to create a new workbook:
objExcel.Workbooks.Add()
Working with Data in an Excel Workbook
Workbooks contain a single worksheet by default. In this section, you manipulate
data in the worksheet. The following describes what you do:
1. Add data to four cells in the worksheet.
2. Select the four cells.
3. Total the selected cells, and place the sum in a fifth cell.
4. Bold all five cells.
474 HOUR 22: Controlling Other Applications Using Automation
Did you
Know?
To manipulate cells in the worksheet, you manipulate the ActiveCell object, which
is an object property of the Application object. Entering data into a cell involves first
selecting a cell and then passing data to it. You select a cell by calling the Select
method of the Range object; the Range object is used to select one or more cells. The
Select method accepts a starting column and row and an ending column and row. If
you want to select only a single cell, as we do here, you can omit the ending column
and row. After the range is set, you pass data to the FormulaR1C1 property of the
ActiveCell object (which references the cell specified by the Range object). Setting
the FormulaR1C1 property has the effect of sending data to the cell. Sound confusing?
Well, it is to some extent. Programs that support automation are often vast and complex,
and programming them is usually far from intuitive.
If the program you want to automate has a macro builder (as most Microsoft products
do), you can save yourself a lot of time and headaches by creating macros of
the tasks you want to automate. Macros are actually code, and in the case of
Microsoft products, they’re VBA code, which is similar to Visual Basic 6 code.
Although this code won’t port directly to Visual Basic 2010, it’s rather easy to
migrate in most cases, and the macro builder does all or most of the work of
determining objects and members for you.
The following section of code uses the techniques just described to add data to four
cells. Follow these steps now to automate sending the data to Excel:
1. Enter this code into your procedure:
objExcel.Range(“A1”).Select()
objExcel.ActiveCell.FormulaR1C1 = “75”
objExcel.Range(“B1”).Select()
objExcel.ActiveCell.FormulaR1C1 = “125”
objExcel.Range(“C1”).Select()
objExcel.ActiveCell.FormulaR1C1 = “255”
objExcel.Range(“D1”).Select()
objExcel.ActiveCell.FormulaR1C1 = “295”
The next step is to have Excel total the four cells. You do this by using the Range
object to select the cells, activating a new cell in which to place the total, and
then using FormulaR1C1 again to create the total by passing it a formula rather
than a literal value.
2. Enter this code into your procedure:
objExcel.Range(“A1:D1”).Select()
objExcel.Range(“E1”).Activate()
objExcel.ActiveCell.FormulaR1C1 = “=SUM(RC[-4]:RC[-1])”
3. Select all five cells and bold them. Enter the following statements to accomplish
this:
objExcel.Range(“A1:E1”).Select()
objExcel.Selection.Font.Bold = True
Automating Microsoft Word 475
The last thing you need to do is destroy the object reference by setting the object
variable to Nothing. Excel remains open even though you’ve destroyed the
automation instance (not all servers do this).
4. Add this last statement to your procedure:
objExcel = Nothing
To help ensure that you entered everything correctly, Listing 22.1 shows the procedure
in its entirety.
LISTING 22.1 Code to Automate Excel
Private Sub btnAutomateExcel_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) _
Handles btnAutomateExcel.Click
Dim objExcel As New Excel.Application
objExcel.Visible = True
objExcel.Workbooks.Add()
objExcel.Range(“A1”).Select()
objExcel.ActiveCell.FormulaR1C1 = “75”
objExcel.Range(“B1”).Select()
objExcel.ActiveCell.FormulaR1C1 = “125”
objExcel.Range(“C1”).Select()
objExcel.ActiveCell.FormulaR1C1 = “255”
objExcel.Range(“D1”).Select()
objExcel.ActiveCell.FormulaR1C1 = “295”
objExcel.Range(“A1:D1”).Select()
objExcel.Range(“E1”).Activate()
objExcel.ActiveCell.FormulaR1C1 = “=SUM(RC[-4]:RC[-1])”
objExcel.Range(“A1:E1”).Select()
objExcel.Selection.Font.Bold = True
objExcel = Nothing
End Sub
Testing Your Client Application
Now that your project is complete, press F5 to run it, and click the button to automate
Excel. If you entered the code correctly, Excel starts, data is placed in four cells, the
total of the four cells is placed in a fifth cell, and all cells are made bold, as shown in
Figure 22.3.
Automating Microsoft Word
Now you’ll build another simple application that automates Microsoft Word 2007.
Begin by creating a new project titled Automate Word. Right-click Form1.vb in the
Solution Explorer, choose Rename, and then change the default form’s name to
MainForm.vb. Next, change the form’s Text property to Automate Word.
476 HOUR 22: Controlling Other Applications Using Automation
FIGURE 22.3
You can control
almost every
aspect of Excel
when using its
object model.
By the
Way
Creating a Reference to an Automation Library
To automate Microsoft Word, you have to reference Word’s object library, just as you
did for Excel. Follow these steps to reference the library:
1. Choose Project, Automate Word Properties to display the Project Properties.
2. Click the References tab to display the active references for the project.
3. Below the list of existing references (and above the list of imported namespaces),
click the Add button to display the list of available references.
4. On the COM tab, locate Microsoft Word 12.0 Object Library, and double-click it.
This selects the library and closes the Add Reference dialog box. The COM reference
appears in the References list in the Project Properties window.
If you don’t see Microsoft Word 12.0 Object Library in your list of available COM
references, you probably don’t have Word 2007 installed. As with the Excel example,
you can use the 11.0 Object Library of Word if you have Word 2003 installed.
5. In the lower part of the References page is a check box list of Imported Namespaces.
Use the scrollbar for this list box (not the main scrollbar for the page) to
locate and check Microsoft.Office.Interop. This most likely is one of the last
items in the list.
Automating Microsoft Word 477
Property Value
Name btnAutomateWord
Location 90, 128
Size 104, 23
Text Automate Word
6. Click Save All on the toolbar.
7. Click MainForm.vb [Design] to return to the Forms Designer.
Creating an Instance of an Automation Server
As with the previous example, all the code for automating Word is placed in a button’s
Click event. Follow these steps to create the button and instantiate a Word
object:
1. Add a button to the form by double-clicking the Button item in the toolbox,
and set the button’s properties as follows:
2. Double-click the button to access its Click event.
3. To work with Word’s object model, you need an instance of Word’s Application
object. Enter the following statement to create a variable that contains an
instance of Word’s Application object:
Dim objWord As New Word.Application
4. As with Excel, Word starts hidden, so the user doesn’t know it’s running.
Because you’ll want to see the fruits of your labor, add this statement to force
Word to show itself:
objWord.Visible = True
5. Next, have Word create a new document by adding this statement to your
procedure:
objWord.Documents.Add()
6. There are many ways to send text to Word. Perhaps the easiest is the
TypeText() method of the Selection object. The Selection object refers to
currently selected text in the Word document. When a new document is created,
it has no text, and the selection object simply refers to the edit cursor at the
478 HOUR 22: Controlling Other Applications Using Automation
By the
Way
FIGURE 22.4
A simple but
effective demonstration
of
automating
Word.
start of the document. Sending text to Word using Select.TypeText() inserts
the text at the top of the document. Enter this statement to send text to Word:
objWord.Selection.TypeText(“This is text from a VB 2010 application.”)
7. The last statement you need to enter sets the Word object to Nothing:
objWord = Nothing
8. Press F5 to run the program. You should see Word start, and then a new document
is created using the text you specified with TypeText(), as shown in
Figure 22.4.
Automating applications, particularly Office products such as Excel and Word,
requires a lot of system resources. If you intend to perform a lot of automation,
you should use the fastest machine with the most memory that you can afford.
Also, be aware that for automation to work, the server application (Excel or Word
in this case) has to be installed on the user’s computer in addition to your application.
Q&A 479
Summary
In this hour, you learned how a program can make available an object model that
client applications can use to manipulate the program. You learned that the first step
in automating a program (server) is to reference the server’s type library. After the
type library is referenced, the server’s objects are available as though they’re internal
Visual Basic objects. As you’ve seen, the mechanics of automating a program aren’t
that difficult—they build on the object-programming skills you’ve already learned in
this book. The real challenge comes in learning the object model of a given server
and in making the most productive use of the objects available.
Q&A
Q. What are some applications that support automation?
A. All the Microsoft Office products, as well as Microsoft Visio, support automation.
You can create a robust application by building a client that uses multiple
automation servers. For example, you could calculate data in Excel and then
format and print the data in Word.
Q. Can you automate a component without creating a reference to a type
library?
A. Yes, but this is considerably more complicated than when you use a type
library. First, you can’t early-bind to objects because Visual Basic doesn’t know
anything about the objects without a type library. This means that you have
no IntelliSense drop-down list to help you navigate the object model, and
Visual Basic doesn’t perform any syntax checking on your automation code;
the chances for bugs in this situation are almost unbearably large. To create a
reference to a server using late binding, you use Visual Basic’s CreateObject()
function.
480 HOUR 22: Controlling Other Applications Using Automation
Workshop
Quiz
1. Before you can early-bind objects in an automation server, you must do what?
2. What is the most likely cause of not seeing a type library listed in the Add References
dialog box?
3. For Visual Basic to use a COM library, what must it create?
4. To manipulate a server via automation, what do you manipulate?
5. To learn about the object library of a component, what should you do?
Answers
1. Add a reference to the server’s type library.
2. The application is not installed.
3. A wrapper around the COM library
4. An object that holds an instantiated object from the server
5. Consult the programmer’s help file for the component.
Exercises
1. Modify the Excel example to prompt the user for a filename to use to save the
workbook. Hint: Consider the Save() method of the Application object.
2. Modify your Excel example so that after summing the four cells, you retrieve
the sum from Excel and then send the value to a new Word document.
Understanding ClickOnce Technology 481
HOUR 23
Deploying Applications
What You’ll Learn in This Hour:
. Understanding ClickOnce technology
. Using the Publish Wizard to create a ClickOnce program
. Testing a ClickOnce install program
. Uninstalling an application you’ve distributed
. Setting Advanced options when creating ClickOnce programs
Now that you’ve learned how to create a Visual Basic application, you’re probably
itching to create a project and send it to the world. Fortunately, Visual Basic includes
the tools you need to create a setup program for your applications. In this hour,
you’ll learn how to use these tools to create a setup program that a user can run to
install an application you’ve developed. In fact, you’ll create a setup program for the
Picture Viewer application you’ve been working on since Hour 1, “Jumping in with
Both Feet: A Visual Basic 2010 Programming Tour.”
Understanding ClickOnce Technology
Microsoft can’t seem to settle on a deployment technology. Before .NET, serious developers
were forced to use third-party applications to build installation programs. Then
Microsoft introduced Windows Installer Technology, in which developers created an
MSI file that installed an application. With Visual Basic 2005, Microsoft introduced
yet another technology: ClickOnce. ClickOnce technology has its drawbacks, mostly
in its lack of flexibility, but it does have some significant improvements over earlier
technologies, and Microsoft has continued to improve it. Many of the improvements
will be appreciated mostly by experienced developers who have been battling install
technology for some time. This hour covers the highlights of ClickOnce technology.
After you understand what the ClickOnce technology offers, I’ll walk you through
creating a ClickOnce program that installs your Picture Viewer program on a user’s
computer.
482 HOUR 23: Deploying Applications
The following points are highlights of the new ClickOnce technology:
. ClickOnce is designed to bring the ease of deploying a web application to the
deployment of desktop applications. Traditionally, to distribute a desktop
application you had to touch every client computer, running the setup program
and installing the appropriate files. Web applications, on the other
hand, need to be updated in only one place: on the web server. ClickOnce provides
desktop applications with update functionality similar to that of web
applications.
. Applications deployed with ClickOnce can update themselves. They can check
the Web for a newer version and install the newer version automatically.
. ClickOnce programs update only necessary files. With previous installation
technologies, entire applications had to be reinstalled to be updated.
. ClickOnce allows applications to install their components in such a way that
they don’t interfere with other installed applications. In other words, they are
self-contained applications. With Windows Installer deployments (that is, the
“old way”), applications shared components such as custom controls. If one
application mistakenly installed an older version of a component, deleted a
component, or installed an incompatible version of a component, it would
break other installed applications that used the shared component.
. ClickOnce programs do not require the user to have administrative permissions.
With Windows Installer deployments, users needed administrative permissions
to install an application. Trust me—this is a serious issue, and I’m
glad to see ClickOnce address it.
. A ClickOnce application can be installed in one of three ways: from a web
page, from a network file share, or from media such as a CD-ROM.
. A ClickOnce application can be installed on a user’s computer, so it can be run
when the user is offline. Or it can be run in an online-only mode, where it
doesn’t permanently install anything on the user’s computer.
Using the Publish Wizard to Create a
ClickOnce Application
Now you’ll create a ClickOnce program that installs the Picture Viewer program
you’ve been building throughout this book. Begin by opening the Picture Viewer
project from Hour 20, “Working with the Registry and Text Files,” and then follow
these steps:
Using the Publish Wizard to Create a ClickOnce Application 483
1. Choose Project, Publish Picture Viewer. This displays the Publish Wizard, shown
in Figure 23.1. This page is used to specify where you want the ClickOnce file
created.
2. Specify the location for the ClickOnce install files. Be aware that you must
enter a path that already exists; Visual Basic does not create a path for you. If
you specify an invalid path, you get a Build error at the end of the wizard.
3. On the next page of the Publish Wizard, shown in Figure 23.2, specify the
method users are to employ to install your program. Although you can specify
FIGURE 23.1
The Publish Wizard
is used to
create ClickOnce
programs.
FIGURE 23.2
Users can install
your application
in one of three
ways.
484 HOUR 23: Deploying Applications
a website or UNC share, choose From a CD-ROM or DVD-ROM for this example
and click Next.
4. The next page of the Publish Wizard, shown in Figure 23.3, asks you whether
the application will check for updates. If your application supports this feature,
select the appropriate option button and specify a location where the update
files will be placed. The Picture Viewer is a simple application and does not
need this level of functionality, so leave the option The Application Will Not
Check for Updates selected and click Next.
5. The final page of the Publish Wizard, shown in Figure 23.4, is simply a confirmation
page. Verify that the information displayed is how you want it. Don’t
be concerned about the formatting applied to your path. Visual Basic modifies
it to create a valid UNC path. Click Finish to create the install.
When you click Finish, the Publish Wizard creates the ClickOnce application and
opens the folder containing the install files, as shown in Figure 23.5. To distribute this
application, you simply burn the contents of this folder, including the subfolder and
its contents, to a CD-ROM or DVD-ROM and send it to a user.
FIGURE 23.3
ClickOnce applications
can
update themselves
if you
design them to
do so.
Using the Publish Wizard to Create a ClickOnce Application 485
FIGURE 23.4
Make sure that
everything is correct
before you
finish the
wizard.
FIGURE 23.5
These files (and
the subfolder)
make up the
ClickOnce program.
486 HOUR 23: Deploying Applications
Testing Your Picture Viewer ClickOnce
Install Program
Run the Setup.exe file in your designated ClickOnce folder to start the install. You
might notice a quick window that shows an animated dialog indicating that the
computer is being checked for a valid Internet connection. The first dialog you can
interact with is a security warning, as shown in Figure 23.6. The publisher of the
component is listed as unknown because the file isn’t digitally signed.
Digitally signing a file is beyond the scope of this book, but if this is important to
you, you can learn more at http://www.verisign.com/. (Search for “code signing.”)
Did you
Know?
Click Install to install the Picture Viewer.
That’s it! There are no additional dialog boxes to deal with. In fact, the Picture
Viewer launches automatically when the install completes.
Now, open your Start menu and you will see a new folder. It most likely will be titled
Picture Viewer (see Figure 23.7). In that folder is the Picture Viewer application shortcut
the user can click to run the program.
Uninstalling an Application You’ve
Distributed
All Windows applications should provide a facility to easily be removed from the
user’s computer. Most applications provide this functionality in the Add/Remove Programs
dialog box, and yours is no exception. In fact, all ClickOnce programs automatically
create an entry in the Uninstall or Change a Program dialog box. Follow
these steps to uninstall the Picture Viewer program:
FIGURE 23.6
All ClickOnce
programs launch
with a security
warning.
Uninstalling an Application You’ve Distributed 487
FIGURE 23.7
Users can find
your program in
their Program
Files, just as
with commercial
applications.
1. Choose Start, Control Panel.
2. Locate the Uninstall a program link, and click it.
3. Scroll down in the dialog box until you find the Picture Viewer program, as
shown in Figure 23.8.
4. To uninstall the program, click to select it and then click Uninstall/Change.
You are given an opportunity to confirm or cancel, as shown in Figure 23.9. If
you select OK, the program is uninstalled.
FIGURE 23.8
Your program
can be uninstalled
from
within the Uninstall
or Change
a Program dialog
box.
488 HOUR 23: Deploying Applications
FIGURE 23.9
You cannot undo
an uninstall—
you must reinstall
the
application to
use it again.
Setting Advanced Options for Creating
ClickOnce Programs
The Publish Wizard is the easiest way to create a ClickOnce program, but it doesn’t
give you access to all the features of ClickOnce. To view all the available settings,
right-click the project name in the Solution Explorer and choose Properties. Next,
click the Publish tab, and you see a page of publishing options, as shown in Figure
23.10. Using this page, you can specify prerequisites, such as whether to install the
.NET Framework, which is required to run any .NET application. (By default, the Publish
Wizard creates your ClickOnce application such that it installs the .NET Framework
from the Web if the user performing the install doesn’t have the Framework
installed.) The Publish Wizard walks you through many of these options, but you
gain the most control by setting your options here and clicking the Publish Now button,
which appears at the bottom right of the Publish page.
FIGURE 23.10
Advanced Click-
Once settings
can be set on
the Publish tab
of the Project
Properties.
Workshop 489
Summary
In this hour, you learned about ClickOnce and why Microsoft has moved to Click-
Once from Windows Installer technology. You also learned how to use the Publish
Wizard to create a ClickOnce program to distribute an application you’ve built using
Visual Basic. Creating installs for robust applications requires a lot more effort and,
in many cases, more tools. But the skills you learned in this hour enable you to distribute
most projects that you’ll build as a beginner with Visual Basic 2010.
Q&A
Q. How can I create the great installation wizards I see other install applications
use?
A. If you want to create robust installations that gather user input in wizards,
make changes to the Registry, enable you to include additional files, create
shortcuts, and so on, you need to use a tool that uses the Windows Installer
technology.
Q. Should I assume that a user will always have the .NET Framework on her
computer?
A. Generally, no. When distributing updates to your project, it’s probably a safe
bet that the user has installed the .NET Framework. For an initial installation,
you should specify the .NET Framework as a prerequisite (note that this is set
by default).
Workshop
Quiz
1. What is the name of the install technology?
2. True or false: ClickOnce programs can be self-updating.
3. True or false: ClickOnce programs have more flexibility than Windows Installer
programs.
4. What are the three ways a user can install a ClickOnce program?
5. What wizard is used to create a ClickOnce program?
490 HOUR 23: Deploying Applications
Answers
1. ClickOnce
2. True
3. False. Windows Installer technology provides much more flexibility than Click-
Once programs.
4. From a web page, from a network file share, or from media such as a CD-ROM
5. The Publish Wizard
Exercises
1. Use the Publish Wizard to create an install for the Automate Excel project in
Hour 22, “Controlling Other Applications Using Automation.” Try installing
the ClickOnce program on a computer that doesn’t have Excel, and see what
happens when you run the program.
2. If you have access to a web server, use the Publish Wizard to deploy the Picture
Viewer to the web server, and then install the application on a different computer
from the web server.
The .NET Framework 491
HOUR 24
The 10,000-Foot View
What You’ll Learn in This Hour:
. Understanding the .NET Framework
. Understanding the common language runtime
. How Visual Basic 2010 uses the Microsoft intermediate language
. Using Visual Studio .NET namespaces
. Understanding the common type system
. Understanding garbage collection
You know a lot about Visual Basic 2010 now. You can create projects, you can use
forms and controls to build an interface, and you know how to add menus and toolbars
to a form. You’ve also learned how to create modules and procedures and how
to write code to make things happen. You can use variables, make decisions, perform
looping, and even debug your code. Now you might be wondering, “Where to next?”
In fact, this is the number one question I receive from readers via emails.
Throughout this book, I’ve focused my discussions on Visual Basic. When it comes to
Microsoft’s .NET Framework, however, Visual Basic is just part of the picture. This
hour provides an overview of Microsoft’s .NET Framework so that you can see how
Visual Basic relates to .NET as a whole. After completing this hour, you’ll understand
the various pieces of .NET and how they’re interrelated. I hope you’ll be able to combine
this information with your current personal and professional needs to determine
the facets of .NET that you want to explore in more detail.
The .NET Framework
The components and technology that make up Microsoft .NET are collectively called
the .NET Framework. The .NET Framework is composed of numerous classes and
includes components such as the Common Language Runtime, Microsoft Intermedi-
492 HOUR 24: The 10,000-Foot View
ate Language, and ADO.NET. The following sections explain the various pieces that
make up the .NET Framework.
Common Language Runtime
A language runtime allows an application to run on a target computer; it consists of
code that’s shared among all applications developed using a supported language. A
runtime contains the “guts” of language code, such as code that draws forms to the
screen, handles user input, and manages data. The runtime of .NET is called the
common language runtime.
Unlike runtimes for other languages, the common language runtime is designed as a
multilanguage runtime. For example, both C# and Visual Basic use the common
language runtime. In fact, currently more than 15 language compilers are being
developed to use the common language runtime.
Because all .NET languages share the common language runtime, they also share
the same IDE, forms engine, exception-handling mechanism, garbage collector (discussed
shortly), and much more. One benefit of the multilanguage capability of the
common language runtime is that programmers can leverage their knowledge of a
given .NET language.
For example, some developers on a team might be comfortable with Visual Basic,
whereas others are more comfortable with C#. Because both languages share the
same runtime, both can be integrated to deliver a single solution. In addition, a common
exception-handling mechanism is built into the common language runtime so
that exceptions can be thrown from code written in one .NET language and caught
in code written in another.
Code that runs within the common language runtime is called managed code
because the code and resources that it uses (variables, objects, and so on) are fully
managed by the common language runtime. Visual Basic is restricted to working
only in managed code, but some languages (such as C++) can drop to unmanaged
code—code that isn’t managed by the common language runtime.
Another advantage of the common language runtime is that all .NET tools share the
same debugging and code-profiling tools. In the past, Visual Basic was limited in its
debugging tools, whereas applications such as C++ had many third-party debugging
tools available. All languages now share the same tools. This means that as
advancements are made to the debugging tools of one product, they’re made to tools
of all products because the tools are shared. This goes beyond debugging tools. Add-
Microsoft Intermediate Language 493
By the
Way
ins to the IDE such as code managers, for example, are just as readily available to
Visual Basic as they are to C#—or any other .NET language, for that matter.
Although Microsoft hasn’t announced any official plans to do so, it’s possible that
it could produce a version of the common language runtime that runs on other
operating systems, such as Macintosh OS or Linux. If this occurs, the applications
that you’ve written for Windows should run on a newly supported operating
system with little or no modification.
Microsoft Intermediate Language
As you can see in Figure 24.1, all .NET code, regardless of the language syntax used,
compiles to Intermediate Language (IL) code. IL code is the only code that the common
language runtime understands; it doesn’t understand C#, Visual Basic, or any
other developer syntax. IL gives .NET its multilanguage capabilities; as long as an
original source language can be compiled to IL, it can become a .NET program. For
example, people have developed a .NET compiler for COBOL—a mainframe language
with a long history. This compiler takes existing COBOL code and compiles it
to IL so that it will run within the .NET Framework, using the common language runtime.
COBOL itself isn’t a Windows language and doesn’t support many of the features
found in a true Windows language (such as a Windows Forms engine), so you
can imagine the excitement of COBOL programmers when they first learned of being
able to leverage their existing code and programming skills to create powerful Windows
applications.
Visual Basic .Net
Source Code
Visual Basic .Net
Syntax Compiler
C# Source Code
Intermediate Level code (IL)
Processor-Specific Machine-Level Instructions
C# Syntax
Compiler
Just-in-time Compiler (JITter)
Language XXX
Source Code
Language XXX
Syntax Compiler
FIGURE 24.1
These are the
steps taken to
turn developer
code into a running
component.
494 HOUR 24: The 10,000-Foot View
A potential drawback of IL is that it can be susceptible to reverse compilation.
This has many people questioning the security of .NET code and the security of
the .NET Framework in general. If code security is a serious concern for you, I
encourage you to research this matter on your own.
By the
Way
Generating IL code isn’t the final step in the process of compiling and running an
application. For a processor (CPU) to execute programmed instructions, those instructions
must be in machine language format. When you run a .NET application, a justin-
time compiler (called a JITter) compiles the IL to machine-language instructions
that the processor can understand. IL code is processor independent, which again
brings up the possibility that JITters could be built to create machine code for computers
that are using something other than Intel-compatible processors. If Microsoft were
to offer a common language runtime for operating systems other than Windows,
many of the differences would lie in how the JITter would compile IL.
As .NET evolves, changes made to the common language runtime will benefit all
.NET applications. For example, if Microsoft finds a way to further increase the speed
at which forms are drawn to the screen by making improvements to the common
language runtime, all .NET applications will immediately benefit from the improvement.
However, optimizations made to a specific syntax compiler, such as the one
that compiles Visual Basic code to IL, are language specific. This means that even
though all .NET languages compile to IL code and use the common language runtime,
it’s possible for one language to have small advantages over another because of
how the language’s code is compiled to IL.
Namespaces
As mentioned earlier in this book, the .NET Framework is composed of classes—many
classes. Namespaces are the way .Net creates a hierarchical structure of all these
classes, and they help prevent naming collisions. A naming collision occurs when two
classes have the same name. Because namespaces provide a hierarchy, it’s possible to
have two classes with the same name, as long as they exist in different namespaces.
Namespaces, in effect, create scope for classes.
The base namespace in the .NET Framework is the System namespace. The System
namespace contains classes for garbage collection (discussed shortly), exception handling,
data typing, and much more. The System namespace is just the tip of the iceberg.
There are literally dozens of namespaces. Table 24.1 lists some of the more
common namespaces, many of which you’ve used in this book. All the controls
Namespaces 495
you’ve placed on forms and even the forms themselves belong to the
System.Windows.Forms namespace. Use Table 24.1 as a guide; if a certain namespace
interests you, I suggest that you research it further in the Visual Studio .NET
online help.
TABLE 24.1 Commonly Used Namespaces
Namespace Description
Microsoft.VisualBasic Contains classes that support compilation and code
generation using Visual Basic.
System Contains fundamental classes and base classes that
define commonly used value and reference data types,
event handlers, interfaces, attributes, and exceptions.
This is the base namespace of .NET.
System.Data Contains classes that constitute the ADO.NET
architecture.
System.Diagnostics Contains classes that enable you to debug your
application and to trace the execution of your code.
System.Drawing Contains classes that provide access to the Graphical
Device Interface (GDI+) basic graphics functionality.
System.IO Contains classes that allow reading from and writing to
data streams and files.
System.Net Contains classes that provide a simple programming
interface to many of the protocols found on the
network.
System.Security Contains classes that provide the underlying structure
of the common language runtime security system.
System.Web Contains classes that provide interfaces that enable
browser/server communication.
System.Windows.Forms Contains classes for creating Windows-based
applications that take advantage of the rich user
interface features available in the Microsoft Windows
operating system.
System.XML Contains classes that provide standards-based support
for processing XML.
All Microsoft-provided namespaces begin with either System or Microsoft. Other
vendors can provide their own namespaces, and it’s possible for you to create
your own custom namespaces as well, but that’s beyond the scope of this book.
By the
Way
496 HOUR 24: The 10,000-Foot View
Common Type System
The common type system in the common language runtime is the component that
defines how data types are declared and used. The common language runtime’s
capability to support cross-language integration to the level it does is largely due to
the common type system. In the past, each language used its own data types and
managed data in its own way. This made it difficult for applications developed in different
languages to communicate because no standard way existed for passing data
between them.
The common type system ensures that all .NET applications use the same data types.
It also provides for self-describing type information (called metadata) and controls all
the data manipulation mechanisms so that data is handled (stored and processed) in
the same way among all .NET applications. This allows data (including objects) to be
treated the same way in all .NET languages.
Garbage Collection
Although I’ve talked a lot about objects (you can’t talk about anything .NET-related
without talking about objects), I’ve avoided discussing the underlying technical
details of how .NET creates, manages, and destroys objects. Although you don’t need
to know the complex minutiae of how .NET works with objects, you do need to
understand a few details of how objects are destroyed.
As discussed in previous hours, setting an object variable to Nothing or letting it go
out of scope destroys the object. However, as mentioned in Hour 16, “Designing
Objects Using Classes,” this isn’t the whole story. The .NET platform uses a garbage
collector to destroy objects. The specific type of garbage collection that .NET implements
is called reference-tracing garbage collection. Essentially, the garbage collector
monitors the resources a program uses. When consumed resources reach a defined
threshold, the garbage collector looks for unused objects. When the garbage collector
finds an unused object, it destroys it, freeing all the memory and resources the object
was using.
An important thing to remember about garbage collection is that releasing an object
by setting it to Nothing or letting an object variable go out of scope doesn’t mean
that the object is destroyed immediately. The object isn’t destroyed until the garbage
collector is triggered to go looking for unused objects.
Summary 497
Further Reading
Readers often ask me what books they should read next. I do not have a specific
answer to this question because it depends entirely on who is asking. Chances are
you’re learning .NET for one of the following reasons:
. School
. Professional requirements
. Personal interest or as a hobby
Your reasons for learning Visual Basic have a lot to do with where you should proceed
from here. If you’re just learning Visual Basic as a hobby, take a route that
interests you, such as web development or database development. If you’re looking
to advance your career, consider the companies you want to work for. What types of
things are they doing—security, databases, web development? How can you make
yourself more valuable to those companies? Instead of just picking a direction,
choose a goal and move in that direction.
If a subject simply does not jump out at you, my recommendation is that you learn
how to program databases. Get a book dedicated to your database of choice (mine is
Microsoft SQL Server). Most applications these days use databases, and database
skills are always a plus! Database programming and database design are really two
different subjects. If you really want to make yourself valuable, you should learn
how to properly design, normalize, and optimize databases, in addition to programming
them for users to access.
Summary
Now that you’ve completed this book, you should have a solid working understanding
of developing applications with Visual Basic. Nevertheless, you’ve just embarked
on your journey. One of the things I love about developing applications for a living
is that there’s always something more to learn, and there’s always a better approach
to a development problem. In this hour, you saw the bigger picture of Microsoft’s
.NET platform by seeing the .NET Framework and its various components. Consider
the information you learned in this hour a primer; what you do with this information
and where you go from here is entirely up to you.
I wish you the best of luck with your programming endeavors!
This page intentionally left blank
A
accelerator keys, 198
accept buttons, 154-156
AcceptButton property, 155-156
AcceptsReturn property, 150
ActiveCaption system color, 394
ActiveCaptionText system
color, 394
ActiveCell objects, 474
ActiveX controls. See user controls
Add() method, 73
addition operations, 270
ADO.NET
ConnectionString property,
454-455
DataAdapter objects, 452,
456-457
databases
closing data source connections,
455
connecting to, 453-455
DataRow objects, 459-460
DataSet objects, 452
DataTable objects, 452, 456
creating, 458
creating records, 463-464
deleting records, 464
editing records, 462
navigating records,
460-462
populating, 458
referencing fields in
DataRows, 459-460
SqlConnection objects,
452-453
SqlDataAdapter objects,
456-457
System.Data namespace, 452
aligning
controls, 125-126
text in text boxes, 148
anchoring controls, 128-130
And operator, 276
applications
automating
Excel (MS), 470-476
Word (MS), 475-477
Index
ClickOnce technology,
481-482
distributed applications, uninstalling,
486-487
publishing, 482-484, 488
testing, 486
arithmetic operations
addition, 270
comparison operators,
273-274
division, 271
exponentiation, 271
modulus arithmetic, 271
multiplication, 271
negation, 270
order of operator precedence,
determining, 272-273
subtraction, 270
arrays
declaring, 251
defining, 237
dimensioning, 251
multidimensional arrays,
252-254
variables, referencing,
251-252
attribute flags (files), 421
Auto Hide property, 36
auto-hiding design windows, 36
automation
defining, 469
Excel (MS)
cell manipulation in workbooks,
473-475
forcing showing
of Excel, 473
instances of automation
server creation, 472
library reference creation,
470-472
testing applications,
475-476
workbook creation, 473
system requirements, 478
Word (MS), 475
instances of automation
server creation, 477
library reference creation,
476-477
autosizing controls, 128-130
B
BackColor property, 41, 99-100
BackgroundImage property,
100-102
backgrounds (forms)
adding images to, 100-101
changing color, 98-99
BaseDirectory() method, 444
binding object references to
variables, 357
creating new objects,
360-361
early binding, 360
late binding, 358-359
bitmaps, Graphics objects, 391
block (structure) scope, 254-255
Boolean data type, 239-240
Boolean logic
And operator, 276
defining, 269, 274-275
If...Then constructs, 294
Not operator, 276
Or operator, 276-277
Xor operator, 276-277
borders (forms), customizing,
105-107
BorderStyle property, 41
break points, 329-331
browsing files, 22-24
build errors, 326-328
buttons, 81
accept buttons, 154-156
Buttons collection, 208-210
cancel buttons, 154-156
check boxes, 156-157
creating, 154
radio buttons, 159-160
toolbar buttons, 212
user messages
determining which button
is clicked, 372
specifying buttons in,
369-371
Byte data type, 239
C
cancel buttons, 154-156
CancelButton property, 156
Case Else statements, 302
Case statements, 299-302
casting data between data types,
241-242
cells (Excel), 473-475
Char data type, 239
check boxes, 156-157
500
applications
checked menu items, creating,
200-201
CheckState property, 156
circles, drawing, 398
class modules, 48, 218
classes
defining, 348
encapsulating code/data, 348
namespaces, 494-495
objects, creating, 350-351
adding properties to classes,
352-356
exposing object attributes
as properties, 352-356
objects, instantiating
binding references to variables,
357-361
releasing object references,
362
standard modules versus, 349
Clear() method, 69, 398
clearing
lists (list boxes), 165-166
nodes from hierarchical
lists, 190
Click events, 24-25, 81, 84,
153-155, 382, 477
ClickOnce technology, 481-482
Publish Wizard, 482-484, 488
clients, defining, 469
Clng() function, 332-334
Close() method, 455
closing
For...Next loops, 310
forms, 112-113
windows, 10
CLR (Common Language
Runtime), 492-493
code
comments, adding, 324-325
debugging, 323-324
adding comments to code,
324-325
break points, 329-331
build errors, 326-328
creating error handlers via
Try...Catch...Finally structures,
336-339
handling exceptions in
error handlers, 339-344
Immediate window,
331-335
On Error statements, 337
runtime errors, 326-328
encapsulating via
classes, 348
labels, 304
modules
class modules, 218
defining, 217
writing, 21
browsing files example,
22-24
terminating programs
example, 24-25
code procedures
calling, 225-230
creating, 219-220
declaring procedures with
return values, 224-225
declaring procedures without
return values,
220-224
exiting, 231-232
infinite recursion, 232
collections, 73-74. See also
objects
Buttons collection, 208-210
Controls collections, 73-75
iterative processing, 72
color
background color, changing,
98-99
color properties, 42-43
dithered colors, 44
system colors, 393-396
columns
DataRows, 459
enhanced lists, creating
columns for, 183
COM components, 472
combo boxes, 161, 168-170
CommandBuilder objects, 457
comments, adding to code,
324-325
common language runtime (CLR),
492-493
common type systems, 496
comparison operators, 273-274
compilers, defining, 238
concatenation, 90, 278-279
ConnectionString property,
454-455
constants, 244
benefits of, 242-243
defining, 237, 242-243
naming, 246
referencing, 243
syntax of, 243
constants
501
containers, 157-158
context menus, 204-206
context-sensitive help, 53
Continue Do statements, 317
Continue For statements, 312
control box buttons, adding to
forms, 103-104
control objects, 58
Control system color, 394
ControlDark system color, 394
ControlLight system color, 395
controls, 145
aligning, 125-126
anchoring, 128-130
autosizing, 128-130
buttons
accept buttons, 154-156
cancel buttons, 154-156
check boxes, 156-157
creating, 154
radio buttons, 159-160
check boxes, 156-157
combo boxes, 161, 168-170
containers, 157-158
Context Menu Strip
control, 205
drawing, 119
enhanced lists, creating, 182
adding list items, 183-186
columns, 183
determining selected list
items, 186
removing list items,
186-187
forms, adding to, 16-18, 20-
21, 38-39
double-clicking controls in
toolbox, 118
dragging controls from
toolbox, 118
drawing controls, 119
forms, organizing on
aligning controls, 125-126
anchoring controls,
128-130
autosizing controls,
128-130
creating tab orders,
131-133
grid (size and snap),
120-121
layering controls, 133
selecting groups of controls,
123-125
setting property values for
groups of controls, 127
sizing controls, 126
Snap to Lines, 122-123
spacing groups of controls,
126
Graphics objects, 390
Group Box control, 157-158
group boxes, 157-158
groups of controls
setting property
values, 127
spacing, 126
hierarchical lists,
creating, 187
adding nodes, 188-189
clearing all nodes, 190
removing nodes, 190
Image List control, 180-181
invisible-at-runtime controls,
20-21
Label control, 145-147
layering, 133
list boxes, 161
adding items to lists, 163
clearing lists, 165-166
manipulating items at
design time, 162
manipulating items at runtime,
162-168
removing items from lists,
164-165
retrieving information from
selected items in lists,
166-167
sorting lists, 167-168
List View control, 182-187
Menu Strip control, 196-198
nonvisual controls, 20-21
OpenFileDialog control,
409-415
creating file filters, 412
displaying Open File dialog,
412-413
OpenFileDialog controls, 17,
20, 23, 26
Panel control, 157-158
panels, 157-158
Picturebox controls, 17-19
SaveFileDialog control, 409,
413-415
selecting groups of controls,
123-125
sizing, 126-130
Status Bar control, 213-214
Tab control, 177-180
502
containers
tab orders, creating, 131-133
tabbed dialog boxes, creating,
177-180
text boxes, 146
adding scrollbars to, 150
aligning text in, 148
common events, 153
creating multiline text
boxes, 148-149
creating password
fields, 152
limiting number of characters
entered, 151
Timer control, 174-176
Toolbar control, 211
ToolStrip control, 208-210
Tree View control, 187-190
two button controls, 17
visible controls, adding to
forms, 18
Controls collections, 73-75
ControlText system
color, 395
Copy() method, 417
copying files, 416-417
CreateDirectory() method, 424
CreateGraphics
method, 68-69
CreateSubKey() method, 431
custom dialog boxes, creating,
373-375
customizing Visual Basic, 32
docking design windows,
34-36
floating design windows, 34
hiding/displaying design
windows, 33-36
D
DashStyle property, 392
data types, 238
Boolean data type, 239-240
Byte data type, 239
casting data between data
types, 241-242
Char data type, 239
Date data type, 239-240,
283-284
Decimal data type, 239-240
determining, 238
Double data type, 239-240
Integer data type, 239-240
Long data type, 239-240
naming conventions,
259-260
Object data type, 239-240
prefixes, 259-260
Registry (Windows), 429
SByte data type, 239
selecting, 240
Short data type, 239-240
Single data type, 239-240
String data type, 239-240
UInteger data type, 239
ULong data type, 239
UShort data type, 239
DataAdapter objects, 452,
456-457
databases, 451-452
ADO.NET, 452
closing data source connections,
455
DataAdapter objects, 452,
456-457
database connections,
453-455
DataRows, 459-460
DataSet objects, 452
DataTable objects, 452,
456-458
SqlConnection
objects, 452
SqlDataAdapter objects,
456-457
records
creating, 463-464
deleting, 464
editing, 462
navigating, 460-462
running, 465
DataSet objects, 452
DataTable objects, 452, 456
creating, 458
creating records, 463-464
DataRows, referencing fields
in, 459-460
deleting records, 464
editing records, 462
navigating records, 460-462
populating, 458
Date data type, 239-240
date/time
adding time to specific dates,
285-286
current system date/time,
retrieving, 288
Date data type, 283-284
DateAdd() function, 285-286
DateDiff() function, 286-287
DatePart() function, 287
date/time
503
DateTime structure, 284, 288
file date/time information,
retrieving, 420
formatting, 287-288
intervals between
dates/times, determining,
286-287
IsDate() function, 289
parts of dates, retrieving, 287
subtracting time from specific
dates, 285-286
values as dates, determining
if, 289
Debug.WriteLine()
method, 336
debugging code, 323-324
break points, 329-331
build errors, 326-328
comments, 324-325
error handlers
creating via
Try...Catch...Finally structures,
336-339
handling exceptions,
339-344
Immediate window,
331-335
On Error statements, 337
Registry deployments
(Windows), 437
runtime errors, 326-328
Decimal data type, 239-240
declaration statements
(events), 84
declaring
arrays, 251
objects, 360-361
variables, 244-246
explicit variable declaration,
247-248
static scope, 258-259
Delete() method, 73,
418-419, 424
DeleteSubKey() method, 431
deleting
DataTable object
records, 464
directories (folders), 424
files, 418-419
menu items, 200
objects, 496
Registry keys (Windows), 431
design windows
displaying, 33
docking, 34-36
floating, 34
hiding, 33-36
Desktop system color, 395
dialog boxes
custom dialog boxes, creating,
373-375
tabbed dialog boxes, creating,
177-180
dimensioning
arrays, 251
objects, 360-361
variables, 244, 246
directories (folders)
BaseDirectory() method, 444
CreateDirectory()
method, 424
creating, 424
deleting, 424
Directory object, 424
existence of,
determining, 424
moving, 424
displaying
design windows, 33
forms
maximized state, 109-110
minimized state,
109-110
normal state, 109-110
specific initial
position, 111
lists via list boxes, 161
adding items
to lists, 163
clearing lists, 165-166
manipulating items at
design time, 162
manipulating items at runtime,
162-168
removing items from lists,
164-165
retrieving information from
selected items in lists,
166-167
sorting lists, 167-168
log files, 445-447
messages via
MessageBox.Show() function,
367-368
determining which button
is clicked, 372
guidelines for creating
good messages, 373
specifying buttons/icons,
369-371
504
date/time
Open File dialog, 412-413
properties (objects), 11
Registry options
(Windows), 434
static text via Label control,
145-147
text files, 445-447
toolbars, 37
windows, 10
Dispose() method, 71
distributable components,
defining, 6
distributed applications,
uninstalling, 486-487
dithered colors, 44
division operations, 271
DLL, 9
Do...Loop loops
Continue Do
statements, 317
creating, 316-320
ending, 316-317
example of, 318-320
docking
design windows, 34-36
toolbars, 38
Double data type, 239-240
double-clicking in Visual Studio
2010, 10
drag handles (toolbars), 38
DrawEllipse() method, 398
drawing controls, 119
DrawLine() method, 397
DrawRectangle() method,
70-71, 398
DrawString() method, 399
drop-down lists
creating via combo boxes,
168-170
toolbar buttons, 212
early binding, 358-360
editing DataTable object
records, 462
E
ellipses, drawing, 398
Else statements, 296
ElseIf statements, 297-299
Enabled property, 149
encapsulating code/data via
classes, 348
End If statements, 23-24,
274, 295
Else statements, 296
False expressions, 296
ending programs, writing code
for, 24-25
enhanced lists,
creating, 182
columns, 183
list items
adding, 183-186
determining selected
items, 186
removing, 186-187
error handlers
creating via
Try...Catch...Finally
structures, 336-339
exceptions, handling,
339-344
events, 22
build example, 87
event handler creation,
89-92
user interface
creation, 88
Click events, 24-25, 81, 84,
153-155, 382, 477
declaration statements, 84
event handlers, creating, 22,
89-90, 92
event-driven programming, 79
FormClosed events, 455
invoking (triggering), 80
objects, 81
OS (operating
systems), 82
user interaction, 81
methods versus, 80
MouseDown events, 84-86,
153, 382
MouseEnter events, 382
MouseHover events, 382
MouseLeave events, 382
MouseMove events, 90,
153, 382
MouseUp events, 153, 382
MultilineChanged events, 81
names, 92
object events, accessing,
83-85
Paint events, 82, 405
parameters, 84-87
recursive events, 82
Resize events, 405
TextChanged event, 81, 153
events
505
Excel (MS) automation, 470
cell manipulation in workbooks,
473-475
forcing showing of Excel, 473
instances of automation server
creation, 472
library reference creation,
470-472
testing applications, 475-476
workbook creation, 473
executable components, 9
existing projects, opening, 32
Exists() method, 416, 424
Exit For statements, 312
Exit Try statements, 340
exiting For...Next loops early, 312
explicit variable declaration,
247-248
exponentiation operations, 271
expressions, variables in, 246-247
F
False expressions, 296
file filters, creating, 412
files
attributes
attribute flags, 421
retrieving, 420-421
browsing, 22-24
copying, 416-417
date/time information,
retrieving, 420
deleting, 418-419
existence of, determining, 416
File object, 415-423
log files
creating, 443-444
displaying, 445-447
testing, 447
moving, 417-418
naming, 418
properties, retrieving,
422-423
renaming, 418
text files
creating, 443-444
displaying, 445-447
reading, 441-442
testing, 447
writing, 439-441
Filter property, 21
filters, creating, 412
finding help, 53
floating design windows, 34
folders (directories)
BaseDirectory() method, 444
CreateDirectory() method, 424
creating, 424
deleting, 424
Directory object, 424
existence of, determining, 424
moving, 424
Font objects, 399
Font property, 42
For...Next loops, 309
closing, 310
Continue For statements, 312
creating, 312-315
example of, 312-315
Exit For statements, 312
exiting early, 312
For statements, 310
initiating, 310
Next statements, 310
specifying increment
values, 311
Step statements, 311
formatting date/time, 287-288
FormBorderStyle property,
105-107
FormClosed events, 455
forms, 58
backgrounds
adding images to,
100-101
changing color, 98-99
borders, 105-107
closing, 112-113
control box buttons, adding,
103-104
controls, adding, 16-21,
38-39
double-clicking controls in
toolbox, 118
dragging controls from
toolbox, 118
drawing controls, 119
controls, organizing
aligning controls, 125-126
anchoring controls,
128-130
autosizing controls,
128-130
creating tab orders,
131-133
grid (size and snap),
120-121
506
Excel (MS) automation
layering controls, 133
selecting groups of controls,
123-125
setting property values for
groups of controls, 127
sizing controls, 126
Snap to Lines, 122-123
spacing groups of controls,
126
defining, 9, 48, 95
displaying in
maximized state, 109-110
minimized state, 109-110
normal state, 109-110
specific initial
position, 111
Graphics objects, 390
graphics, persisting
on forms, 400
icons, assigning, 14, 103
maximize buttons, adding,
103-104
MDI (multiple-document interface)
forms, 136-139
menus, 196-198
adding buttons to toolbars,
208-210
assigning shortcut keys to
menu items, 206-207
button drop-down
menus, 212
checked menu items,
200-201
context menus, 204-206
creating menu items, 199
deleting menu items, 200
moving menu items, 200
programming, 202-204
programming
toolbars, 211
status bars, 213-214
toolbars, 208-212
minimize buttons, adding,
103-104
modality, 108
naming, 96
nonmodal windows, 134
scrollable forms, 134-136
showing, 107-108
sizing, 15, 107-110
startup forms,
configuring, 140
taskbar, preventing forms
from appearing in, 112
text bars, 97-98
title bar, 13
topmost nonmodal
windows, 134
transparent forms, 134
unloading, 112-113
Windows Forms Applications,
8-9
FormulaR1C1 property, 474
functions. See also methods
methods, exposing functions
as, 356
OpenPicture() function, 443
G
Get construct, 354
GetAttributes() method, 420-421
GetValue() method, 432
global (namespace) scope,
256-257
GoTo statements, 304-305
graphics
adding images to backgrounds,
100-101
circles, drawing, 398
Clear() method, 69
CreateGraphics method,
68-69
creating, 400-406
Dispose() method, 71
DrawRectangle() method,
70-71
ellipses, drawing, 398
example of, 400-406
forms, persisting
graphics on, 400
Graphics object, 389-391
Image List control, storing
images in, 180-181
lines, drawing, 397
pens, 392-393
rectangles, drawing,
396-398
system colors, 393-396
text, drawing, 399
GrayText system color, 395
grid (size and snap)
GridSize property, 120
LayoutMode property, 120
organizing controls on forms,
120-121
ShowGrid property, 120-122
SnapToGrid property,
120-122
grid (size and snap)
507
Group Box control, 157-158
group boxes, 157-158
grouping controls, 123-125
H
handlers (event), creating,
89-92
Height property, 15
help
context-sensitive help, 53
finding, 53
further reading, 497
hiding
design windows, 33, 36
Excel (MS), 473
toolbars, 37
windows, 10
hierarchical lists,
creating, 187
adding nodes, 188-189
clearing all nodes, 190
removing nodes, 190
Highlight system color, 395
HighlightText system color, 395
hives (Registry), 428
HKEY_CLASSES_ROOT
node, 428
HKEY_CURRENT_CONFIG
node, 428
HKEY_CURRENT_USER node,
428, 431
HKEY_LOCAL_MACHINE node,
428, 431
HKEY_USERS node, 428
hotkeys, 198
I
icons
forms, assigning icons to,
14, 103
user messages, specifying
icons in, 369-371
IDE (integrated development environment),
7
If statements, 274
If...End constructs, 435
If...Then constructs, 274, 293-294
Else statements, 296
ElseIf statements, 297
End If statements, 295
expressions
ElseIf statements, 299
evaluating expressions for
multiple values, 298
executing False expressions,
296
False expressions, 296
IsNumeric() function, 294
nesting, 297-298
IL (Intermediate Language),
493-494
images. See graphics
Immediate window, 331-335
InactiveBorder system
color, 395
InactiveCaption system
color, 395
InactiveCaptionText system
color, 395
infinite recursion, procedures
and, 232
Inflate() method, 397
initializing variables, 262-265
InputBox() function, 377-379
installation (setup) programs
ClickOnce technology and,
481-484, 488
Publish Wizard (ClickOnce
technology), 482, 484, 488
testing, 486
instantiating objects, 68
binding references to variables,
357-361
releasing object
references, 362
instantiating objects
Instr() function, 281-282
Integer data type, 239-240
IntelliSense, 62
interaction (program/user)
custom dialog boxes, creating,
373-375
keyboards, 379-382
MessageBox.Show() function,
displaying messages via,
367-368
determining which button
is clicked, 372
guidelines for creating
good messages, 373
specifying buttons/icons,
369-371
mouse events, 382-385
user information, obtaining,
377-379
Invalidate() method, 405
invisible-at-runtime controls, 20-21
invoking (triggering)
events, 80
objects, 81
508
Group Box control
OS (operating systems), 82
user interaction, 81
methods (objects), 66-67
IsDate() function, 289
IsNumeric() function, 294
iterative processing, 72
J-K-L
keyboards, user/program
interaction, 379-382
Label control, 145-147
labels (code), 304
late binding, 358-359
layering controls, 133
LayoutMode property, 120
Len() function, 279
libraries
defining, 76
type (object) libraries, 470
line continuation characters, 71
lines, drawing, 397
list boxes, 161. See also lists
design time, manipulating
items at, 162
runtime, manipulating items
at, 162-168
lists
adding items to, 163
clearing, 165-166
drop-down lists, creating via
combo boxes, 168-170
enhanced lists, creating, 182
adding list items, 183-186
columns, 183
determining select list
items, 186
removing list items,
186-187
hierarchical lists,
creating, 187
adding nodes, 188-189
clearing all nodes, 190
removing nodes, 190
List View control, 182-187
removing items from,
164-165
retrieving information from
selected items, 166-167
sorting, 167-168
Tree View control, 187-190
literal values, passing to variables,
246
local (procedure-level) scope, 255
log files
creating, 443-444
displaying, 445-447
testing, 447
Long data type, 239-240
loops
Do...Loop loops
Continue Do
statements, 317
creating, 316-320
ending, 316-317
example of, 318-320
For...Next loops, 309
closing, 310
Continue For
statements, 312
creating, 312-315
example of, 312-315
Exit For statements, 312
exiting early, 312
For statements, 310
initiating, 310
Next statements, 310
specifying increment values,
311
Step statements, 311
iterative processing, 72
recursive loops, 232
While...End loops, 320
M
magic numbers, 242
managing projects, 45-46
math operations
addition, 270
comparison operators,
273-274
division, 271
exponentiation, 271
modulus arithmetic, 271
multiplication, 271
negation, 270
order of operator precedence,
determining,
272-273
subtraction, 270
maximize buttons, adding to
forms, 103-104
maximized state, displaying
forms in, 109-110
MaximumSize property, 107
MaxLength property, 151
MaxLength property
509
MDI (multiple-document
interface) forms, 136-139
Me.Close() statements, 25
memory leaks, 71
Menu system color, 395
menus
context menus,
204-206
creating, 196-198
drop-down menus, 212
menu items
assigning shortcut keys
to, 206-207
checked menu items,
200-201
creating, 199
deleting, 200
moving, 200
Menu Strip control,
196-198
programming, 202-204
status bars, 213-214
toolbars
adding buttons to toolbars,
208-210
button drop-down
menus, 212
programming, 211
MenuText system color, 395
MessageBox.Show() method, 52,
74, 302, 367-373
messages, displaying via
MessageBox.Show() function,
367-368
buttons
determining which button
is clicked, 372
guidelines for creating
good messages, 373
specifying, 369-371
icons, 369-371
metadata, 496
methods
Add(), 73
BaseDirectory(), 444
Clear(), 69, 398
Close(), 455
Copy(), 417
CreateDirectory(), 424
CreateGraphics(), 68-69
CreateSubKey(), 431
Debug.WriteLine(), 336
defining, 65
Delete(), 73, 418-419, 424
DeleteSubKey(), 431
Dispose(), 71
DrawEllipse(), 398
DrawLine(), 397
DrawRectangle(), 70-71, 398
DrawString(), 399
dynamism, 67
events versus, 80
Exists(), 416, 424
functions, exposing as methods,
356
GetAttributes(), 420-421
GetValue(), 432
Inflate(), 397
Invalidate(), 405
invoking (triggering), 66-67
MesageBox.Show(), 52, 74,
302, 367-373
Move(), 417-418, 424
ReadToEnd(), 442
SetValue(), 432
ShowDialog(), 23
SourceFileExists(), 416
Write(), 440
WriteLine(), 440-441
Microsoft IL (Intermediate
Language), 493-494
Microsoft.VisualBasic.Left() function,
279-280
Microsoft.VisualBasic.Right() function,
280
Mid() function, 280-281
minimize buttons, adding to
forms, 103-104
minimized state, displaying forms
in, 109-110
MinimumSize property, 107
modality of forms, 108
module-level scope, 255
modules
class modules, 218
defining, 48, 217
standard modules, classes
versus, 349
modulus arithmetic
operations, 271
monitors, Visual Studio 2010
resolution requirements, 10
mouse
Click events, 382
MouseDown events, 382
MouseEnter events, 382
MouseHover events, 382
MouseLeave events, 382
MouseMove events, 382
510
MDI (multiple-document interface) forms
MouseUp events, 382
user/program interaction,
382-385
Visual Studio 2010, doubleclicking
in, 10
MouseDown event, 84-86, 153
MouseMove event, 90, 153
MouseUp event, 153
Move() method, 417-418, 424
moving
directories (folders), 424
files, 417-418
menu items, 200
multidimensional arrays, 252-254
Multiline property, 148
multiline text boxes, creating,
148-149
MultilineChanged events, 81
multiplication operations, 271
My.Computer.Registry object,
430-433
N
Name property, 11-13, 41
namespace (global) scope,
256-257
namespaces (.NET Framework),
452, 494-495
naming
constants, 246
data types, 259-260
events, 92
files, 418
forms, 96
naming collisions, 494
objects, 11-13, 260
projects, 8
scope, 257, 260
variables, 246
navigating
DataTable object records,
460-462
Visual Basic, 32
Visual Studio 2010, 10
negation operations, 270
nesting
If...Then constructs,
297-298
Select Case constructs, 304
.NET Framework, 491
CLR (Common Language
Runtime), 492-493
common type systems, 496
IL (Intermediate Language),
493-494
namespaces, 494-495
objects, deleting, 496
Visual Basic’s
relationship to, 6
New Project dialog, 7-8, 30
Next statements, 310
nodes (list)
adding, 188-189
clearing, 190
removing, 190
nonmodal windows, 134
nonvisual controls, 20-21
normal state, displaying forms in,
109-110
Not operator, 276
numbers, magic, 242
O
object (type) libraries, 470
Object data type, 239-240
object models, 469
objects
ActiveCell objects, 474
building example, 67-69, 71
classifying, 11
CommandBuilder
objects, 457
control objects, 58
creating via classes, 350-356
DataAdapter objects, 452,
456-457
DataSet objects, 452
DataTable objects, 452,
456-458
creating records, 463-464
deleting records, 464
editing records, 462
navigating records,
460-462
populating, 458
referencing fields in
DataRows, 459-460
declaring, 360-361
defining, 11, 57-58
dimensioning, 360-361
Directory object, 424
events
accessing, 83-85
invoking (triggering), 81
File object, 415-423
Font objects, 399
form objects, 58
Graphics object, 389-391
objects
511
instantiating, 68
binding references to variables,
357-361
releasing object references,
362
iterative processing, 72
libraries, 76
lifetime of, 362-363
methods. See methods
My.Computer.Registry object,
430-433
naming, 11-13, 260
.NET Framework, 496
Object Browser, 75-76
prefixes, 260
properties. See properties
Range objects, 474
scope, browsing, 76
selecting, 40
SqlConnection objects,
452-453
SqlDataAdapter objects,
456-457
Startup object, 140
StreamReader object,
441-442
StreamWriter object, 439-441
testing example, 72
Office (MS)
Excel automation, 470-476
Word automation, 475-477
OLE controls. See user controls
On Error statements, 337
Opacity property, 134
Open File dialog, displaying,
412-413
OpenFileDialog control, 17, 20,
23, 26, 409-415
file filters, creating, 412
Open File dialog, displaying,
412-413
opening existing projects, 32
OpenPicture() function, 443
operator precedence (arithmetic
operations), 272-273
Or operator, 276-277
P
Paint events, 82, 405
Panel control, 157-158
panels, 157-158
parameters (events), 84-87
code procedures, passing
parameters in, 228-230
defining, 85
multiple parameters in
events, 85
password fields, creating, 152
PasswordChar property, 152
pens, 392-393
peripherals
keyboards, 379-382
mouse, 382-385
PictureBox controls, 17-19
pictures. See graphics
prefixes
data types, 259-260
objects, 260
scope, 260
procedure-level (local)
scope, 255
procedures, 51
calling, 225-230
creating, 219-220
declaring procedures with
return values, 224-225
declaring procedures without
return values,
220-224
exiting, 231-232
infinite recursion, 232
program interaction
custom dialog boxes, creating,
373-375
keyboards, 379-382
MessageBox.Show() function,
displaying messages via,
367-368
determining which button
is clicked, 372
guidelines for creating
good messages, 373
specifying buttons/icons,
369-371
mouse events, 382-385
user information, obtaining,
377-379
programs
defining, 47
projects versus, 47
running, 25-27
terminating, 24-25
projects
components of, 47-48
creating, 7-9, 30-31
defining, 6, 47
DLL, 9
executable components, 9
512
objects
files
adding, 49-50
removing, 49-50
grouping, 47
managing, 45-46
naming, 8
New Project dialog, 7-8, 30
opening existing projects, 32
programs versus, 47
properties, 48-49
Recent Projects dialog, 30
saving, 13-14
properties (objects), 40
AcceptButton, 155-156
AcceptsReturn, 150
Auto Hide, 36
BackColor, 41, 99-100
BackgroundImage, 100-102
BorderStyle, 41
button creation, 61-64
CancelButton, 156
changing, 40-42
CheckState, 156
classes, adding to, 352-353
color properties, 42-44
ConnectionString, 454-455
defining, 11, 58
descriptions, viewing, 44
displaying, 11
Enabled, 149
Filter, 21
Font, 42
FormBorderStyle, 105-107
FormulaR1C1, 474
GridSize, 120
Height, 15
LayoutMode, 120
MaximumSize, 107
MaxLength, 151
MinimumSize, 107
Multiline, 148
Name, 11-13, 41
Opacity, 134
PasswordChar, 152
read-only properties, 60,
355-356
readable properties, 354
referencing, 59-60
ScrollBars, 150
setting, 48-49
ShowGrid, 120-122
ShowInTaskbar, 112
Size, 42
SnapToGrid, 120-122
StartPosition, 109-111
TabIndex, 132-133
TabStop, 133
Text, 13, 24
TextAlign, 148
unchangeable properties, 60
viewing, 40
Width, 15
WindowState, 109-110
WordWrap, 150
writable properties, creating,
354-355
write-only properties, creating,
355-356
Properties window (Visual Studio
2010), 10
Publish Wizard, 482-484, 488
Q-R
Quit button, 24-25
radio buttons, 159-160
Range objects, 474
read-only properties, 60, 355-356
readable properties, 354
reading text files, 441-442
ReadToEnd() method, 442
Recent Projects dialog, 30
rectangles, drawing, 396-398
recursive events, 82
recursive loops, 232
referencing
array variables, 251-252
automation libraries
Excel (MS), 470-472
Word (MS), 476-477
constants, 243
Registry (Windows), 427
accessing via
My.Computer.Registry
object, 430
creating Registry keys,
430-431
deleting Registry keys, 431
getting Registry key values,
432-433
setting Registry key values,
432-433
data types, 429
deployments, 437
displaying options from, 434
hives, 428
HKEY_CLASSES_ROOT
node, 428
Registry (Windows)
513
HKEY_CURRENT_CONFIG
node, 428
HKEY_CURRENT_USER node,
428, 431
HKEY_LOCAL_MACHINE node,
428, 431
HKEY_USERS node, 428
keys
creating, 430-431
deleting, 431
getting values, 432-433
setting values,
432-433
saving options to, 435
stored options, 435-436
structure of, 428-429
removing
items from lists (list boxes),
164-165
list items from enhanced
lists, 186-187
nodes from hierarchical
lists, 190
project files, 49-50
renaming files, 418
Replace() function, 283
reserved words, 246
Resize events, 405
resolution (monitors), 10
running programs, 25-27
runtime errors, 326-328
S
SaveFileDialog control, 409,
413-415
saving
projects, 13-14
Registry options
(Windows), 435
SByte data type, 239
scope
block (structure) scope,
254-255
browsing, 76
defining, 254
global (namespace) scope,
256-257
limiting, 258
module-level scope, 255
name conflicts, 257
naming conventions, 260
prefixes, 260
procedure-level (local)
scope, 255
static scope, 258-259
scrollable forms, 134-136
scrollbars, 150
Select Case constructs
Case Else statements, 302
Case statements, 299-302
example of, 300-303
MessageBox.Show() statements,
302
nesting, 304
uses for, 303-304
values, evaluating more than
one, 299-300
selecting groups of controls,
123-125
servers, defining, 469
Set construct, 354-355
setup (installation) programs
ClickOnce technology and,
481-484, 488
testing, 486
SetValue() method, 432
shapes, drawing
circles, 398
ellipses, 398
lines, 397
rectangles, 396-398
Short data type, 239-240
shortcut keys, assigning to menu
items, 206-207
ShowDialog() method, 23
ShowGrid property, 120-122
showing forms, 107-108
ShowInTaskbar property, 112
Single data type, 239-240
size and snap (grid)
GridSize property, 120
LayoutMode property, 120
organizing controls on forms,
120-121
ShowGrid property, 120-122
SnapToGrid property, 120-122
Size property, 42
sizing
controls, 126-130
docked design windows, 35
forms, 15, 107-110
MaximumSize property, 107
MinimumSize property, 107
toolbars, 38
Snap to Lines property, 122-123
SnapToGrid property, 120-122
Solution Explorer, 45-46
514
Registry (Windows)
solutions
creating, 47
defining, 6, 47
sorting lists (list boxes), 167-168
SourceFileExists() method, 416
spaces, removing from beginning
and end of strings, 282
spacing groups of controls, 126
SqlConnection objects,
452-453
SqlDataAdapter objects,
456-457
standard modules, classes
versus, 349
Start page (Visual Studio 2010),
7-8, 30
starting Visual Studio 2010, 7
StartPosition property, 109-111
startup forms, configuring, 140
Startup object, 140
statements. See specific
statements
static scope, 258-259
static text, displaying via Label
control, 145-147
Status Bar control, 213-214
Step statements, 311
stopping programs, 24-25
stored Registry options
(Windows), 435-436
storing images in Image List control,
180-181
StreamReader object, 441-442
StreamWriter object, 439-441
strict typing, 247-250
String data type, 239-240
strings
concatenating, 278-279
number of characters in,
determining, 279
replacing text within, 283
retrieving text from
left side, 279-280
right side, 280
within strings, 280-281
spaces, removing from beginning
and end
of strings, 282
strings within strings, determining,
281-282
structure (block) scope, 254-255
subtraction operations, 270
support
context-sensitive help, 53
finding, 53
further reading, 497
system colors, 393-396
system date/time, retrieving, 288
System namespace, 494
System.Data namespace, 452
T
Tab control, 177, 179-180
tab order (controls), 131-133
tabbed dialog boxes, creating,
177-180
TabIndex property, 132-133
TabStop property, 133
taskbar
forms, preventing from
appearing in taskbar, 112
ShowInTaskbar property, 112
technical support
context-sensitive help, 53
finding, 53
further reading, 497
terminating programs, 24-25
testing
Excel automation, 475-476
installation (setup)
programs, 486
log files, 447
Registry deployments
(Windows), 437
text files, 447
text
ActiveCaptionText system
color, 394
ControlText system color, 395
drawing via DrawString()
method, 399
Font objects, 399
Font property, 42
GrayText system color, 395
HighlightText system
color, 395
InactiveCaptionText system
color, 395
MaxLength property, 151
MenuText system color, 395
static text, displaying via
Label control, 145-147
strings
replacing text within
strings, 283
retrieving text from left
side of strings, 279-280
retrieving text from right
side of strings, 280
text
515
retrieving text from within
strings, 280-281
text bars (forms), displaying
text on, 97-98
text files
creating, 443-444
displaying, 445-447
reading, 441-442
testing, 447
writing, 439-441
TextAlign property, 148
text bars, displaying text on,
97-98
text boxes, 146
aligning text in, 148
common events, 153
limiting number of characters
entered, 151
multiline text boxes, creating,
148-149
password fields,
creating, 152
scrollbars, adding to, 150
Text property, 13, 24
Textbox controls, 81
TextChanged event, 81, 153
time/date
adding time to specific dates,
285-286
current system date/time,
retrieving, 288
Date data type, 283-284
DateAdd() function,
285-286
DateDiff() function, 286-287
DatePart() function, 287
DateTime structure,
284, 288
file time/date information,
retrieving, 420
formatting, 287-288
intervals between
times/dates, determining,
286-287
IsDate() function, 289
parts of dates, retrieving, 287
subtracting time from specific
dates, 285-286
values as dates, determining
if, 289
Timer control, 81, 174-176
title bar (forms), 13
toolbars
displaying, 37
docking, 38
drag handles, 38
hiding, 37
sizing, 38
Toolbar control, 211
ToolStrip control, 208-210
toolbox
closing, 10
double-clicking controls in
toolbox, 118
dragging controls from toolbox,
118
opening, 10
transparent forms, 134
triggering (invoking)
events, 80
objects, 81
OS (operating systems), 82
user interaction, 81
methods (objects), 66-67
True statements, 274
Try...Catch...Finally structures, creating
error handlers, 336-339
Try...End Try structures, 337-340
two button controls, 17
type (object) libraries, 470
U
UInteger data type, 239
ULong data type, 239
uninstalling applications,
486-487
unloading forms, 112-113
user controls, 48
user interaction
custom dialog boxes, creating,
373-375
keyboards, 379-382
MessageBox.Show() function,
displaying messages via,
367-368
determining which button
is clicked, 372
guidelines for creating
good messages, 373
specifying buttons/icons,
369-371
mouse events, 382-385
user information, obtaining,
377-379
user interfaces, creating (event
building example), 88
UShort data type, 239
516
text
V
variables, 60
creating, 261-262
declaring, 244-246
explicit variable declaration,
247-248
static scope, 258-259
defining, 237
dimensioning, 244-246
expressions, 246-247
initializing, 262-265
naming, 246
object variables, binding, 357
creating new objects,
360-361
early binding, 360
late binding, 358-359
passing literal values to, 246
referencing, 251-252
storing values in, 51
strict typing, 247-250
viewing properties (objects),
40, 44
visible controls, adding
to forms, 18
Visual Basic
customizing, 32
docking design windows,
34-36
floating design
windows, 34
hiding/displaying design
windows, 33-36
navigating, 32
.NET Framework, Visual
Basic’s relationship to, 6
Visual Studio 2010, 7
closing windows, 10
displaying windows, 10
double-clicking in, 10
hiding windows, 10
monitor resolution requirements,
10
navigating, 10
Properties window, 10
Start page, 7-8, 30
starting, 7
Toolbox window, 10
W-X-Y-Z
While...End loops, 320
Width property, 15
Window system color, 395
windows, 10
Windows Forms
Applications, 8-9
Windows Registry. See Registry
WindowState property, 109-110
wizards, Publish Wizard,
482-484, 488
Word (MS) automation, 475-477
WordWrap property, 150
workbooks (Excel)
cell manipulation in,
473-475
creating, 473
writable properties (objects),
354-355
Write() method, 440
write-only properties (objects),
355-356
WriteLine() method, 440-441
writing
code, 21
browsing files example,
22-24
terminating programs
example, 24-25
text files, 439-441
Xor operator, 276-277
yes/no options via check boxes,
156-157
yes/no options via check boxes
517