Switching main forms

[jmcilhinney]

Here is a simple method to allow you to start an app with one form and then close that form and open another without exiting the app. I have implemented it with two forms here but you could have as many as you like. This is what would have been termed a dialogue-based application in times gone by I think. You would make the module the startup object for the project:

Module Module1
 
    Public mainForm As Form 'The current primary form.
 
    Sub Main()
        'Start the app with a new instance of Form1
        mainForm = New Form1
 
        'Keep showing the current main form until there isn't one.
        Do
            Application.Run(mainForm)
        Loop While Not mainForm Is Nothing
    End Sub
 
End Module
 
Public Class Form1
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        'Open a new main form and close this one.
        mainForm = New Form2
        Me.Close()
    End Sub
 
    Private Sub Form1_Closing(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles MyBase.Closing
        If mainForm Is Me Then
            'This is the main form so let the app exit.
            mainForm = Nothing
        End If
    End Sub
 
End Class
 
Public Class Form2
 
    Private Sub Form2_Closing(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles MyBase.Closing
        If mainForm Is Me Then
            'This is the main form so let the app exit.
            mainForm = Nothing
        End If
    End Sub
 
End Class

Note that you cannot use this method to switch the main form to one that is already open because the call to Application.Run will try to display it. This will cause an exception to be thrown if the form is already displayed.