Why LeftDoubleClick does not work for a slider - wpf

Question

I have a slider that represents position in an audio file. The user requirement is to automatically play when the user double clicks on the slider.
When I use this:
<Slider.InputBindings>
<MouseBinding Gesture="LeftDoubleClick" Command="{Binding PlayCommand}" />
</Slider.InputBindings>
The Play Command is not called. However, if I use this:
<Slider.InputBindings>
<MouseBinding Gesture="RightClick" Command="{Binding PlayCommand}" />
</Slider.InputBindings>
or this
<Slider HorizontalAlignment="Stretch" (...) MouseDoubleClick="slider1_MouseDoubleClick" >
</Slider>
The play command is called.
What prevents the use of the gesture with the double click, yet allows the right click gesture or the double click event to be called?

Answer 1

OK, I think I've figured out what's happening here:
The RepeatButton in the Track is intercepting the MouseLeftButtonDown event and setting Handled = true. Note that the MouseLeftButtonDown event is an off-shoot of MouseDown, so if you set Handled for one, you're really setting it for both. In this case, the mouse-down events are being handled when ClickCount = 1, and the act of marking the events as Handled prevents those events' handlers from being invoked on the second click (i.e., when ClickCount = 2). Input gestures are evaluated on the MouseDown event, so suppressing the MouseDown handlers for the second click means the Slider won't get probed for input bindings, and commands with double-click gestures will never get a chance to execute.
So, if the mouse-down handlers don't get invoked during the second click, why do the MouseDoubleClick handlers get invoked? Well, it turns out that MouseDoubleClick originates from a class-level handler in Control, and that handler gets invoked even when the original mouse-down event(s) were marked as Handled. Note the last argument to RegisterClassHandler below:
EventManager.RegisterClassHandler(
typeof(Control),
UIElement.MouseLeftButtonDownEvent,
new MouseButtonEventHandler(HandleDoubleClick),
/* handledEventsToo: */ true);
And thus the MouseDoubleClick event gets raised even though the LeftDoubleClick input binding never got a chance to execute. This is perhaps not the most intuitive behavior, and I'm unsure whether it was a conscious design decision or a simple oversight.