Public Class Form1
 
    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) _
      Handles Button1.Click
        Me.OnButton1_Click(sender, e)
    End Sub
 
    Protected Overridable Sub OnButton1_Click(sender As Object, e As EventArgs)
        Debug.WriteLine("Form1_Button1_Click")
    End Sub
 
End Class
 
Public Class MyExtendedForm
    Inherits Form1
 
    Protected Overrides Sub OnButton1_Click(sender As Object, e As _
      System.EventArgs)
        Debug.WriteLine("MyExtendedForm_Button1_Click_Vorher")
        MyBase.OnButton1_Click(sender, e)
        Debug.WriteLine("MyExtendedForm_Button1_Click_Danach")
    End Sub
 
End Class