Visual Basic 2005: A Developer's Notebook

Communicate Between Forms

In previous versions of .NET, you were responsible for tracking every open form. If you didn't, you might unwittingly strand a window, leaving it open but cut off from the rest of your application. VB 2005 restores the beloved approach of VB 6 developers, where there's always a default instance of your form ready, waiting, and accessible from anywhere else in your application.

Note

VB 2005 makes it easy for forms to interact, thanks to the new default instances. This feature is a real timesaver—and a potential stumbling block.

How do I do that?

To access the default instance of a form, just use its class name. In other words, if you've created a form that's named (unimaginatively) Form1, you can show its default instance like this:

Form1.Show( )

This automatically creates an instance of Form1 and then displays it. This instance of Form1 is designated as the default instance.

To communicate between forms, you simply add dedicated public methods. For example, if Form1 needs to be able to refresh Form2, you could add a RefreshData( ) method to Form2, like this:

Public Class Form2
    Private Sub RefreshData( )
        MessageBox.Show("I've been refreshed!")
    End Sub
End Class

You could then call it like this:

Form2.RefreshData( )

This calls the RefreshData( ) method of the default instance of Form2. The fact that RefreshData( ) is a method you added (not an inherited method, like the Show( ) method) makes no difference in how you use it.

You can also get at the forms using the ...