??? Bubbling events are events that travel up the containment hierarchy. For example,
MouseDown is a bubbling event. It??™s raised first by the element that is clicked. Next, it??™s
raised by that element??™s parent, and then by that element??™s parent, and so on, until WPF
reaches the top of the element tree.
CHAPTER 6 n DEPENDENCY PROPERTIES AND ROUTED EVENTS 156
??? Tunneling events are events that travel down the containment hierarchy. They give you
the chance to preview (and possibly stop) an event before it reaches the appropriate
control. For example, PreviewKeyDown allows you to intercept a key press, first at the
window level, and then in increasingly more specific containers until you reach the
element that had focus when the key was pressed.
When you register a routed event using the EventManager.RegisterEvent() method, you
pass a value from the RoutingStrategy enumeration that indicates the event behavior you
want to use for your event.
Because MouseUp and MouseDown are bubbling events, you can now determine what
happens in the fancy label example. When the happy face is clicked, the MouseDown event
fires in this order:
1. Image.MouseDown
2. StackPanel.MouseDown
3. Label.MouseDown
After the MouseDown event is raised for the label, it??™s passed on to the next control
(which in this case is the Grid that lays out the containing window), and then to its parent
(the window).
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