[AS3]as3弱引用addEventListener监听

之前只是知道尽量用强引用,不要用弱引用,因为弱引用会被垃圾回收. 对于flash.utils.Dictionary倒是没有什么疑问.但EventDispatcher.addEventListener就不明白具体是侦听器被回收了,还是侦听者被回收了。
昨天有看了一些文章,又想起这个问题,就想要理解透彻,于是又仔细看了下API文档.

Class-level member functions are not subject to garbage collection, so you can set useWeakReference to true for class-level member functions without subjecting them to garbage collection. If you set useWeakReference to true for a listener that is a nested inner function, the function will be garbge-collected and no longer persistent. If you create references to the inner function (save it in another variable) then it is not garbage-collected and stays persistent.

原来这里的弱引用是对侦听器的(侦听器函数),跟侦听者没有关系. 为了验证这个观点,我做了个小Demo。OK,让我们来一边享受引用,一边学习吧。

package 
{ 
    import flash.display.BitmapData; 
    import flash.display.Sprite; 
    import flash.display.StageAlign; 
    import flash.display.StageScaleMode; 
    import flash.events.Event; 
    import flash.events.ProgressEvent; 
    import flash.media.Sound; 
    import flash.net.URLLoader; 
    import flash.net.URLRequest; 
    import flash.system.System; 
    import flash.text.TextField; 
    import flash.utils.Dictionary; 
 
    /** 
     * 弱引用错误用法示例 
     * @author lite3 
     */ 
    [SWF(width=300, height=100, backgroundColor=0xC7EDCC)] 
    public class WeakReferenceExample extends Sprite  
    { 
        private var weakTxt:TextField; 
        private var strongTxt:TextField; 
        private var sound:Sound = new Sound(); 
        private var arr:Array = []; 
        public function WeakReferenceExample():void  
        { 
            stage.scaleMode = StageScaleMode.NO_SCALE; 
            stage.align = StageAlign.TOP_LEFT; 
            initUI(); 
            sound.load(new URLRequest("http://lite3.googlecode.com/files/WZ_woMenDouShiHaoHaiZi.mp3?" + Math.random())); 
            sound.play(); 
            sound.addEventListener(ProgressEvent.PROGRESS, getHandler(true), false, 0, true); 
            sound.addEventListener(ProgressEvent.PROGRESS, getHandler(false), false, 0, false); 
            sound.addEventListener(Event.COMPLETE, completeHandler); 
 
            // 加快垃圾回收 
            addEventListener(Event.ENTER_FRAME, enterFrameHandler); 
        } 
 
        private function getHandler(isWeak:Boolean):Function 
        { 
            return isWeak ? weakProgressHandler : strongProgressHandler; 
            function weakProgressHandler(e:ProgressEvent):void 
            { 
                weakTxt.text = "弱引用:加载进度:" + ((e.bytesLoaded / e.bytesTotal * 100) >> 0) + "%"; 
            } 
            function strongProgressHandler(e:ProgressEvent):void 
            { 
                strongTxt.text = "强引用:加载进度:" + ((e.bytesLoaded / e.bytesTotal * 100) >> 0) + "%"; 
            } 
        } 
 
        private function enterFrameHandler(e:Event):void  
        { 
            if (System.totalMemory >= 500 * 1024 * 1024) 
            { 
                removeEventListener(Event.ENTER_FRAME, enterFrameHandler); 
            }else 
            { 
                arr.push(new BitmapData(500, 500, true)); 
            } 
        } 
        private function completeHandler(e:Event):void 
        { 
            removeEventListener(Event.ENTER_FRAME, enterFrameHandler); 
            strongTxt.text = "加载已完成!"; 
        } 
 
        private function initUI():void 
        { 
            // CuPlayer.com提示：说明文本 
            var txt:TextField = new TextField(); 
            txt.text = "测试弱引用!\nprogressHandler使用若引用.\ncompleteHandler使用强引用."; 
            txt.width = stage.stageWidth; 
            txttxt.height = txt.textHeight + 4; 
            txt.mouseEnabled = false; 
            addChild(txt); 
 
            // 弱引用文本 
            weakTxt = new TextField(); 
            weakTxt.width = stage.stageWidth; 
            weakTxt.height = 20; 
            weakTxt.text = "弱引用:加载进度:0%"; 
            weakTxt.y = txt.height; 
            addChild(weakTxt); 
 
            // CuPlayer.com提示：强引用文本 
            strongTxt = new TextField(); 
            strongTxt.width = stage.stageWidth; 
            strongTxt.height = 20; 
            strongTxt.text = "强引用:加载进度:0%"; 
            strongTxt.y = txt.height + weakTxt.height; 
            addChild(strongTxt); 
        } 
    } 
}