7: Windows Forms
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When empowered with the following code, this simple form returns whatever is typed in the field when the user clicks OK (first rejecting blank values), or returns a blank string on Cancel:
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Public Class BookEntry Public Function EditTitle( ) As String ' ----- Show the form, and return what the user enters. If (Me.ShowDialog( ) = DialogResult.OK) Then Return BookTitle.Text.Trim Else Return "" End If End Function Private Sub ActCancel_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles ActCancel.Click ' ----- Return a blank title for "Cancel." Me.DialogResult = DialogResult.Cancel ' ----- Continue with EditTitle( ) End Sub Private Sub ActOK_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles ActOK.Click ' ----- Only accept valid titles. If (Len(BookTitle.Text.Trim) = 0) Then MsgBox("Please supply a valid title.") Else Me.DialogResult = DialogResult.OK ' ----- Continue with EditTitle( ) End If End Sub End Class
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To use this form, the parent form calls the EditTitle method, which returns the book title entered by the user.
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Dim newTitle As String = BookEntry.EditTitle( )
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The EditTitle routine shows the form modally with the ShowDialog method, and just sits there until the user closes the form. Closing the form is done through the OK or Cancel button event; setting the form s DialogResult property has the side effect of closing the form. Great!
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Making Forms Useful |
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Once the form closes, execution returns to EditTitle, which does a quick statuscheck before returning the final value. And there we have it: a new public interface for a form s most important return value. We ll use this method a lot in the Library Project application.
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Windows programming really hasn t changed much since Windows 1.0. It still does everything through messages, message queues, and window procedures. What has changed is the way the code is abstracted for the benefit of the programmer. The .NET Framework s package for Windows development, Windows Forms, makes Windows desktop development easy and dare I say it fun!
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This chapter s project code implements the Library Project s basic Main form, as well as the Splash form that appears when the project first starts up. Microsoft, knowing that this was a common need, included support for both main and splash forms in Visual Basic s Application Framework system. By default, this system is enabled through the project properties Application panel (see Figure 7-11).
7: Windows Forms
The Startup form and Splash screen fields indicate the main and splash forms, respectively. It s quick, it s easy, and it s just the thing for us. So, let s get to work. Now would be a great time to load the starter project for 7.
PROJECT ACCESS Load the 7 (Before) Code project, either through the New Project templates or by accessing the project directly from the installation directory. To see the code in its final form, load 7 (After) Code instead.
Con guring the Splash Screen
I ve already added a new form file to the project, named Splash.vb (the form itself is named Splash), including some simple display elements to gussy it up somewhat. Check out the graphic on the form. It s presented through a PictureBox control, but it s stored in the application as a resource, a collection of strings and images attached to your source code. The Resources folder in the Solution Explorer includes this graphics file. It s linked into the picture box through that control s Image property. And it sure makes the form look pretty. Your job will be to attach this form into the startup sequence of the application. Access the project properties Application panel (which you just saw in Figure 7-11), and set the Splash screen field to Splash. This has the side effect of setting My.Application.SplashScreen to the Splash form. Now run the program. You should see the splash screen appear for about 1/100 of a second, quickly replaced by the main form. Hey, what was that Altering the Splash screen field does cause the splash screen to briefly appear, but the application will keep it up only until it thinks the program has done enough preparation for the main form. Since we aren t doing any preparation, it shows the main form right away. Eventually, we will add a bunch of database-related startup code that will consume a little more time. But for now we ll have to fake it. In the Application Framework model, any code you want to process when the program first begins appears in the application s Startup event. This event is one of a small collection of events included with the My hierarchy. The source code for these events appears in the ApplicationEvents.vb file, a file that Visual Studio automatically adds to your project when needed. Use the View Application Events button on the project properties Application panel to open that file s source code.