protected override void OnClick() {
     if (_isOpen)
         return;
     _isOpen = true;
     _dlg = new BrowseLayersDialog();
     _dlg.Closing += bld_Closing;
     _dlg.Owner = FrameworkApplication.Current.MainWindow;
     _dlg.Show();
 }
 void bld_Closing(object sender, System.ComponentModel.CancelEventArgs e) {
     _dlg = null;
     _isOpen = false;
 }