Public Function VarPtr(ByVal o As Object) As Integer
        Dim GC As System.Runtime.InteropServices.GCHandle = _
          System.Runtime.InteropServices.GCHandle.Alloc(o, _
          System.Runtime.InteropServices.GCHandleType.Pinned)
        Dim ret As Integer = GC.AddrOfPinnedObject.ToInt32
        GC.Free()
        Return ret
    End Function
    Private Sub Button20_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button20.Click
        Dim result As String = ""
        Dim p As Integer = VarPtr(result)
        result = InputBox("Eingabe:", "", "")
        Dim isAbort As Boolean = (VarPtr(result) = p)
        If isAbort Then MessageBox.Show("Es wurde auf abbrechen geklickt!")
    End Sub