private void ButtonNumberPad_Click(object sender, RoutedEventArgs e) { NumberPadDlg numberPadDlg = new NumberPadDlg(); bool? result = numberPadDlg.ShowDialog(); if (numberPadDlg.Number.HasValue) { if (numberPadDlg.Number <= 50) { OnCommandAddBlock(numberPadDlg.Number.Value); } else { MessageBox.Show("The number is to large."); } } }