Sets the handler to use for this event type. There can only be one such handler specified at a time. This handler is guaranteed to be called first. This is used for registering the user-defined onFoo event handlers.

Parameters:

<T>		the specific event class of the handler
eventType		the event type to associate with the given eventHandler
eventHandler		the handler to register, or null to unregister

Exceptions:

NullPointerException

if the event type is null