如何使用AddHandler在WPF中的按钮上为LostKeyBoardFocusEvent添加事件处理程序

Question

I am trying to encapsulate some button behaviors and one of which is to add an event handler for event "LostKeyboardFocusEvent", but I got "handler type is mismatched" error in run-time with and SystemArgumentException:

AssociatedObject.AddHandler(Button.LostKeyboardFocusEvent, new DependencyPropertyChangedEventHandler(HandleButtonToolTip), true);

public static void HandleButtonToolTip(object sender, DependencyPropertyChangedEventArgs e)
        {
            //Get tooltip from sender.
            ToolTip tt = (ToolTip)(sender as Control).ToolTip;
            if ((sender as Control).IsKeyboardFocusWithin && !tt.IsOpen)
            {
                ShowButtonTooltip(sender);
            }
            else
            {
                ClearButtonTooltip();
            }
        }

Any help is appreciated!

Answer 1

Change

AssociatedObject.AddHandler(Button.LostKeyboardFocusEvent, new DependencyPropertyChangedEventHandler(HandleButtonToolTip), true);

to

AssociatedObject.AddHandler(Button.LostKeyboardFocusEvent, new RoutedEventHandler(HandleButtonToolTip), true);

And change

public static void HandleButtonToolTip(object sender, DependencyPropertyChangedEventArgs e)

to

public static void HandleButtonToolTip(object sender, RoutedEventArgs e)

Answer 2

Just change the type of the handler from DependencyPropertyChangedEventArgs to KeyboardFocusChangedEventHandler :

AssociatedObject.AddHandler(Button.LostKeyboardFocusEvent, new KeyboardFocusChangedEventHandler(HandleButtonToolTip), true);

...and the type of the EventArgs to KeyboardFocusChangedEventArgs :

public static void HandleButtonToolTip(object sender, KeyboardFocusChangedEventArgs e)
...