MaximumPC 2004 09

How To

 MA XIMUMPC SEPTEMBER 2004

4 Tie the new GUI to the program

The GUI is designed, so let’s get down

to coding. Because this How-To is an

introduction to Windows Forms pro-

gramming, we’re going to show you

the fastest, easiest way to write code to

handle Form1’s button clicks.

In this project we’re going to reuse

the Cryptography class from the previ-

ous programming How-To (if you don’t

have that code, you can download

it from http://www.maximumpc.com/images/

programming_files.zip ). Code reuse is

one of the nice features of object-

oriented programming (OOP), which

was covered in the previous program-

ming How-To. We need to import the

Cryptography class file (Cryptography.

vb) from the MaxPC01 project into our

new MaxPC02 project.

To do so, right-click the project file

MaxPC02 in Solution Explorer and then

select Add, Add Existing Item from the

context menu. Use the dialog box to

navigate to the folder where you have

saved the MaxPC01 project and then

select the Cryptography.vb file. The file

will appear in Solution Explorer under

the MaxPC02 project and will also be

copied to the MaxPC02 directory.

Let’s start off with something easy.

Double-click btnExit. This will take you

to the code view of Form1 and your

cursor should be positioned inside a

special type of method, an event

handler named “btnExit_Click.” Clicking

the Exit button causes or “raises”

the Click event, and the code in this

method “handles” the Click event for

btnExit. As the name suggests, clicking

btnExit will allow us to halt execution

of our application. A really simple way

to achieve this goal is by using

“Application.Exit(),” so that’s the only

code needed for this event handler.

Note that because there’s nothing in

the parenthesis, we’re not giving the

Application.Exit function any variables.

Luckily, Application.

Exit doesn’t require

variables, whenever

it’s called, the app

simple closes.

Now that your

application actually

has some

functionality, you can

test it if you’d like.

From within the IDE,

click the “Start”

button, which is

located in the top

menu area. Visual

Studio will build and,

if there are no errors,

run MaxPC02 for you.

Once you’re finished

gawking at the form,

press the Exit button

and get back to work!

5 Encrypt, decrypt, rinse, repeat

Now, let’s look at how the encryption

function actually works. Double-

click btnEncrypt, which tells Visual

Studio to generate the skeleton of the

btnEncrypt_Click event handler. Turn

your eyes to the sample code on the

next page, and we’ll step through the

code and explain what the function

actually does.

The first thing the program checks

is whether the user has entered any

plaintext by using the methods and

properties of the TextBox class. If you

didn’t catch on earlier, the controls

that you added to your form weren’t

static, immutable widgets but dynamic

class members that

are instantiated

when you run

your program. For

example, txtPlaintext

is a member of

the TextBox class

and has a property

named Text. Not only

can we set the value

of this property at

design time, we can

also get the value of

this property when

the program is run.

This means that

DEFINING TERMS

EVENT: A notification or signal

that is generated by a user action,

such as a button click or a key

press. Events can also be raised by

internal application activities, such

as saving a file or an incoming IM.

CODE VIEW: An editable view of

the code that makes the Windows

Form work.

EVENT HANDLER: A method that

is invoked because of an event.

METHOD: The procedures associ-

ated with an object.

Visual Basic makes it easy to reuse old code. All you have to

do is browse to the location of the previous programming

How-To and add the cryptography.vb file to your new project.

DEFINING TERMS

RUNTIME: Runtime is the moment when a program is

loaded into computer memory.

MESSAGEBOX: A MessageBox in .NET is a small form

used to alert or inform the user using text, icons, or sound.

INTELLISENSE: IntelliSense is a feature of Microsoft’s

Visual Studio that displays information as you type in the

code editor. IntelliSense can supply syntax information as

well as complete words and help you beautify code.

CLASS: A named entity composed of related data and the

methods that act on that data. A class is to an object what

a blueprint is to a house.

OBJECT: An instance or occurrence of a class that has

been created during program execution. Think of a cookie

cutter as the class and the cookies as the objects.