Developing Android Applications with Adobe AIR

Events

EventDispatcher is the base class for all objects that can be a target for events. Many native classes inherit from this class with their own appropriate events:

import flash.display.Sprite;
import flash.events.MouseEvent;

// this draws a button listening to a mouse event
var sprite:Sprite = new Sprite();
sprite.addEventListener(MouseEvent.CLICK, onClick);


import flash.utils.Timer;
import flash.events.TimerEvent;

// this creates a timer listening to a timer event
var timer:Timer = new Timer(1000);
timer.addEventListener(TimerEvent.TIMER , onTimer);
timer.start();

event.target is the object associated with the listening function, or its scope:

function onClick(event:MouseEvent):void {
    trace(event.target); // Sprite
}

function onTimer(event:TimerEvent):void {
    trace(event.target); // Timer
}

The listener object, also known as the event handler, is called when the event happens (the onClick or onTimer functions in the preceding example). It takes a single event instance as a parameter.

The dispatcher, the mechanism that monitors the event, saves a reference of the listener to call back when an event occurs, and its target, in a queue.

You must use removeEventListener to remove these references from memory. Removing the target will not do it:

sprite.removeEventListener(MouseEvent.CLICK, onClick);
timer.removeEventListener(TimerEvent.TIMER , onTimer);

Event Propagation

For display objects, an event starts from the root parent, travels down the tree to the object that is registered, and ...