private void OnExpressionButtonClick(object sender, System.Windows.RoutedEventArgs e)
		{
			ExpressionEditorWindow window = new ExpressionEditorWindow();
			window.ExpressionEditor.Item = this.GridView.CurrentItem;
			window.ExpressionEditor.ExpressionText = this.lastExpressionText;

			window.Closed += this.OnExpressionWindowClosed;

			window.ShowDialog();
		}
		private void OnExpressionButtonClick(object sender, System.Windows.RoutedEventArgs e)
		{
			RadButton expressionButton = (RadButton)sender;
			GroupDescriptorBase descriptor = (GroupDescriptorBase)expressionButton.DataContext;

			ExpressionEditorWindow window = new ExpressionEditorWindow();
			window.ExpressionEditor.Item = this.GridView.CurrentItem;
			window.ExpressionEditor.ExpressionText = GetExpressionText(descriptor);
			window.Closed += this.OnExpressionWindowClosed;
			window.ShowDialog();
		}