ACTIONSCRIPT 3 Developer’s Guide en

ACTIONSCRIPT 3.0 DEVELOPER’S GUIDE
Handling events
package
{
import flash.display.Sprite;
}
public class ClickExample extends Sprite
{
public function ClickExample()
{
var child:ChildSprite = new ChildSprite();
addChild(child);
}
}
import flash.display.Sprite;
import flash.events.MouseEvent;
class ChildSprite extends Sprite
{
public function ChildSprite()
{
graphics.beginFill(0xFF0000);
graphics.drawRect(0,0,100,100);
graphics.endFill();
addEventListener(MouseEvent.CLICK, clickHandler);
}
private function clickHandler(event:MouseEvent):void
{
trace("clickHandler detected an event of type: " + event.type);
trace("the this keyword refers to: " + this);
}
}
When a user interacts with the resulting SWF file by clicking on the red square, Flash Player or AIR generates the
following trace output:
clickHandler detected an event of type: click
the this keyword refers to: [object ChildSprite]
Note that the this keyword refers to the ChildSprite instance named child. This is a change in behavior from
ActionScript 2.0. If you used components in ActionScript 2.0, you may remember that when a class method was passed
in to UIEventDispatcher.addEventListener(), the scope of the method was bound to the component that
broadcast the event instead of the class in which the listener method was defined. In other words, if you used this
technique in ActionScript 2.0, the this keyword would refer to the component broadcasting the event instead of the
ChildSprite instance.
This was a significant issue for some programmers because it meant that they could not access other methods and
properties of the class containing the listener method. As a workaround, ActionScript 2.0 programmers could use the
mx.util.Delegate class to change the scope of the listener method. This is no longer necessary, however, because
ActionScript 3.0 creates a bound method when addEventListener() is called. As a result, the this keyword refers
to the ChildSprite instance named child, and the programmer has access to the other methods and properties of the
ChildSprite class.
Last updated 6/6/2012
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