Event Dispatcher (flash.events.IEventDispatcher)
Flex is driven by events. Event Dispatchers are the key for coordinating the announcement of events and notifying appropriate listeners.
An Event Dispatcher will implement the IEventDispatcher interface and optionally
extend the base EventDispatcher class, both defined in the flash.events package.
The IEventDispatcher interface defines several functions, but the two
key methods are:
dispatchEvent()- Dispatches an event into the event flow so that registered listeners are notifiedaddEventListener()- Registers an event listener object so that the listener receives notification of dispatched event
All Flex controls in the mx.controls package (e.g. Button, TextArea, DataGrid)
and Flex containers in the mx.containers package (e.g. Canvas, VBox)
implement the IEventDispatcher interface and are therefore capable of registering
listeners and dispatching events.
Event Lifecycle: Listening, Dispatching, and Handling
Important event participants:
- dispatcher - the subject of the event
- event - the event object encapsulating details of the event occurence
- listener - the handler function for dealing with an event
Listening for Events
Listening for an event involves registering a callback or handler function with an event dispatcher.
// register a handler function as an event listener dispatcher.addEventListener( "eventType", handlerFunction );
Dispatching Events
Dispatching an event happens when something interesting occurs that an event dispatcher wants to notify listeners of.
// dispatch an event to my listeners dispatchEvent( new Event( "eventType" ) );
Handling Events
Handling and event is the result of an event dispatcher calling a callback or handler function of a listener in response to an event.
// handle an event in a listener public function handlerFunction( event:Event ):void { ... }