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Creating Your First VB.NET Application

You have an open project with one form in it. So far, you haven't done anything to it, so you now need to create the obligatory "Hello World" application. I remember when Microsoft was running around showing the world how you could create a "Hello World" application in VB by typing just one line of code. Well, it's still that easy, but things sure look different now.

Make sure that your form is showing in the work area, and open the Toolbox. Click and drag a button onto the form. Place it wherever you want. So far, this is just like VB6. Now double-click on the button.

Double-clicking on the button causes the code window to open, but it is now just a tab in the work area. The new tab is labeled Form1.vb. You have a lot of code in this window, and it's code that you haven't seen before. In fact, before typing any code at all, you have the code shown in Figure 10. Notice that I have turned on line numbers just for easier referencing. If you want to turn on line numbers as well, go to Tools, Options. Expand the Text Editor node and choose Basic. Check the Line Numbers check box.

Figure 10 The code window shows a significant amount of code before you even start typing.

The first three lines of code are all Imports statements. The Imports statement is what you use to bring in a namespace from a referenced assembly. For now, just think of the namespace as a library of functions.

After the namespaces are imported, you have a public class for Form1. Notice that all the code is inside the Form1 class. Why? Because forms are really just classes, and they have been forever. You might not have ever thought of it that way, but a form is just another class. When a form is displayed, you have just instantiated a class.

Inside the class, the first thing you see is an Inherits statement. This is your first indication of true inheritance in VB.NET. This form is inheriting from the base System.WinForms.Form class. Therefore, System.WinForms.Form holds the true definition of a form, with its properties, methods, and events. You can inherit from this base class and then extend it if you want to do so.

The next piece inside the class is a public sub named New. Notice that it calls a sub named InitializeComponent. The InitializeComponent routine is not immediately seen, but you'll see it in just a moment. The New routine is similar to the Form_Load event procedure you got used to in VB6. Notice that you need to add any of your own code after the call to InitializeComponent.

After the New sub is a Dispose sub, much like the Form_Unload found in VB6. This is the area for the cleanup of anything you might have open. Don't worry about the Overrides keyword for now; it will be covered when you learn more about inheritance.

Next is where things start to get interesting. A gray line runs down the left side of the code, with minus signs at the Class and Sub definitions. Notice that under the Dispose sub is some text that says Windows Form Designer generated code with a plus sign next to it. If you click on that plus sign, you will expand a block of code that is normally collapsed. One thing that the VB.NET editor lets you do is to collapse or expand blocks of code. This can make it easier to see a cleaner view of your code. If you expand the code at line 26 (at least that's the line in Figure 10), you will see a code region and in it you'll see the InitializeComponent sub. In fact, the entire region of code is shown in Listing 1.

NOTE

All this code looks different in Beta 2. Code still sets up the form and the controls, but it has changed. Don't worry about exactly how the code looks, but instead focus on the fact that it exists and understand what it does at a high level.

Listing 1: Code Generated for You by the Windows Form Designer

#Region " Windows Form Designer generated code "

  'Required by the Windows Form Designer
  Private components As _
   System.ComponentModel.Container
  Private WithEvents Button1 As _
   System.WinForms.Button

  Dim WithEvents Form1 As System.WinForms.Form

  'NOTE: The following procedure is required by
  'the Windows Form Designer
  'It can be modified using the Windows
  'Form Designer.
  'Do not modify it using the code editor.
  Private Sub InitializeComponent()
    Me.components = New _
     System.ComponentModel.Container()
    Me.Button1 = New System.WinForms.Button()

    '@design Me.TrayHeight = 0
    '@design Me.TrayLargeIcon = False
    '@design Me.TrayAutoArrange = True
    Button1.Location = New _
     System.Drawing.Point(96, 40)
    Button1.Size = New System.Drawing.Size(75, 23)
    Button1.TabIndex = 0
    Button1.Text = "Button1"

    Me.Text = "Form1"
    Me.AutoScaleBaseSize = New _
     System.Drawing.Size(5, 13)

    Me.Controls.Add(Button1)
  End Sub

#End Region

As you can see, the InitializeComponent routine is in this normally collapsed block, and it is what sets up the controls on the form. Notice that the button has properties set, such as the location and size, and then is added to a controls collection.

Finally, below this region of code is the routine to handle the click event on the button. This looks different from what you have seen before as well. In fact, if you started a new Standard EXE project in VB6, added a button to the form, and then double-clicked the button, your entire project would just show this code:

Private Sub Command1_Click()

End Sub

However, in VB.NET, you will see a lot more code. In fact, the Click event is not even handled until line 57, at least in this example. The declaration of the event procedure is quite different as well. In VB.NET, the event procedure looks like this:

Protected Sub Button1_Click(ByVal sender As Object, _
   ByVal e As System.EventArgs)

End Sub

NOTE

Event procedures have changed in Beta 2. They will all require a Handles clause in Beta 2 and beyond.

Again, don't worry about all the changes for now. Instead, type in the following line of code:

msgbox "Hello, World"

When you move off this line, you will notice that VB.NET automatically adds parentheses around your argument, leaving you with this:

msgbox("Hello, World")

This is one of the first fundamental language changes: Subs and functions require parentheses around the argument. The msgbox command is a function, but in VB6, you did not need parentheses around a parameter if you were ignoring the return value. In VB.NET, you always need the parentheses, so get used to adding them, or at least get used to seeing VB.NET add them for you.

Now it is time to run this rather exciting demonstration and see whether it works. You can click the Start button on the toolbar (it should look familiar), or you can go to the Debug menu and choose Start.

Form1 should load. Click on the button, and you should get a message box to pop up, with the text "Hello, World." However, as you can see in Figure 11, the title of the message box is Error. That's new and certainly not welcome. Close the form and return to the VB.NET IDE.

NOTE

Beta 2 has changed how message boxes work, and the word Error is no longer present in the title. Instead, the title is the name of the application.

The Hello World application running.

Notice that a new window is showing. At the bottom of the screen, an Output window is now open. Figure 12 shows this window. Currently, it shows you all the debug statements. You did not put any debug.print statements into your code, but certain actions by the complier automatically put comments into the debug window.

Figure 12 The new debug window.

Before moving on, you might want to fix the Error in the title of the message box. Return to the one line of code you've written so far, and modify it to look like this:

msgbox("Hello, World", , "My first VB.NET App")

Now that you have added a title to the message box, run the project again, and your message box will have My First VB.NET App as its title. If you think it doesn't get any better than this, hang on.

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