AS3初学者容易迷糊的几个问题
1.Sprite/MovieClip的Enter_Frame事件,不受addChild/removeChild影响
简单点讲:Sprite或MovieClip对象一旦为其添加了Enter_Frame事件监听,对应的Enter_Frame处理函数将会马上被调用,并一直执行下去(不管你是否将其addChild到显示列表,或者将其从显示列表removeChild),直到该对象removeEventListener相应的监听器为止。
同样:MovieClip一旦被new出来,就会自动播放(在未用任何代码stop()的前提下),不管你是否将其addChild或removeChild
注:其它事件也类似,在AS3的世界中,事件一旦被监听,要想停止事件响应,唯一的方法只能是removeEventListener。(这一点跟c#中完全不同,在c#中不管是webform还是winform,一旦按钮被disabled了,肯定就无法触发按钮的Click事件,但在AS3中,组件是否被禁用,跟组件是否能响应事件完全是没有任何关联的!)
测试代码:
var _sprite:Sprite = new Sprite(); _sprite.graphics.lineStyle(1,0); _sprite.graphics.beginFill(0xff0000); _sprite.graphics.drawCircle(0,0,50); _sprite.graphics.endFill(); _sprite.addEventListener(Event.ENTER_FRAME,onSpriteEnterFrame);//实际上:程序执行到这里就会一直不停的跑onSpriteEnterFrame了 function onSpriteEnterFrame(e:Event):void{ trace("我是_Sprite",getTimer()); } addChild(_sprite); _sprite.x = stage.stageWidth/2 ; _sprite.y = stage.stageHeight/2 ; _sprite.addEventListener(MouseEvent.CLICK,onSpriteMouseClick); function onSpriteMouseClick(e:MouseEvent):void{ removeChild(_sprite);//移除自己 _sprite=null;//注意:即使把自身设置为null,原来注册的onSpriteEnterFrame函数仍会一直执行,正确的方法只能用removeEventListener才能移除Enter_Frame事件 //_sprite.removeEventListener(Event.ENTER_FRAME,onSpriteEnterFrame); }
2.ADDED、ADDED_TO_STAGE、REMOVED、REMOVED_FROM_STAGE这几个事件的区别
var _container:Sprite = new Sprite(); _container.addEventListener(Event.ADDED,onAdded); _container.addEventListener(Event.ADDED_TO_STAGE,onAddedToStage); _container.addEventListener(Event.REMOVED,onRemoved); _container.addEventListener(Event.REMOVED_FROM_STAGE,onRemovedFromStage); function onAdded(e:Event):void { trace("onAdded:",e); } function onAddedToStage(e:Event):void { trace("onAddedToStage:",e); } function onRemoved(e:Event):void { trace("onRemoved:",e); } function onRemovedFromStage(e:Event):void { trace("onRemovedFromStage:",e); } addChild(_container); //onAdded: [Event type="added" bubbles=true cancelable=false eventPhase=2] //onAddedToStage: [Event type="addedToStage" bubbles=false cancelable=false eventPhase=2] var _sub:Sprite = new Sprite(); _container.addChild(_sub); //onAdded: [Event type="added" bubbles=true cancelable=false eventPhase=3] /*_container.removeChild(_sub); //onRemoved: [Event type="removed" bubbles=true cancelable=false eventPhase=3]*/ removeChild(_container); //onRemoved: [Event type="removed" bubbles=true cancelable=false eventPhase=2] //onRemovedFromStage: [Event type="removedFromStage" bubbles=false cancelable=false eventPhase=2] _container.removeChild(_sub); //onRemoved: [Event type="removed" bubbles=true cancelable=false eventPhase=3]
区别:
ADDED是子对象被添加到自身时触发,ADDED_TO_STAGE是对象本身被添加到显示列表时触发;类似的:REMOVED当子对象从自身移除时触发,REMOVED_FROM_STAGE是自身从显示列表中移除时触发;
ADDED/REMOVED事件会冒泡,而ADDED_TO_STAGE/REMOVED_FROM_STAGE不冒泡,也就是说每次addChild或removeChild自身时,下面的ADDED/REMOVED事件也会冒泡上来先被触发,然后才触发ADDED_TO_STAGE/REMOVED_FROM_STAGE事件.
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