WPF 设置 Label.MouseDoubleClickEvent

 facLabel.AddHandler(Label.MouseDoubleClickEvent, new MouseButtonEventHandler((o, a) =>
            {
                facLabel.SetValue(Label.VisibilityProperty, Visibility.Collapsed);
                facTextBox.SetValue(TextBox.VisibilityProperty, Visibility.Visible);
                facTextBox.SetValue(TextBox.TextProperty, "abcdefg");
            }));

要写 MouseButtonEventHandler， 不能写 RoutedEvent((o,a)=>....）