| callback | The event handler to add. |
| useTrickleDown | By default, this callback is called during the BubbleUp phase. Pass TrickleDown.TrickleDown to call this callback during the TrickleDown phase. |
Adds an event handler to the instance. If the event handler has already been registered for the same phase (either TrickleDown or BubbleUp) then this method has no effect. The event handler is automatically unregistered after it has been invoked exactly once.
| callback | The event handler to add. |
| userArgs | Data to pass to the callback. |
| useTrickleDown | By default, this callback is called during the BubbleUp phase. Pass TrickleDown.TrickleDown to call this callback during the TrickleDown phase. |
Adds an event handler to the instance. If the event handler has already been registered for the same phase (either TrickleDown or BubbleUp) then this method has no effect. The event handler is automatically unregistered after it has been invoked exactly once.