as3.0加载图片

package {
    import flash.display.MovieClip;
    import flash.net.URLRequest;
    import flash.display.Loader;
    import flash.events.MouseEvent;
    import flash.events.Event;
    import flash.display.SimpleButton;

    public class Main extends MovieClip {

        private var urlR:URLRequest;
        private var loader:Loader;
        private var emptyMc:MovieClip
        private var thisMc:MovieClip
        private var btn:SimpleButton
        private var arr:Array=["达闼","国广健康","泓图","人类遗传","首都医科大"]
        private var num:Number=0
        
        public function Main(_thisMc:MovieClip,_btn:SimpleButton,_emptyMc:MovieClip) {
            emptyMc=_emptyMc
            btn=_btn
            thisMc=_thisMc
            btn.addEventListener(MouseEvent.CLICK,onBtn)
            urlR= new URLRequest();
        }
        private function onBtn(e:MouseEvent){
            loader=new Loader();
            urlR.url = arr[num]+".jpg";
            loader.load(urlR)
            loader.contentLoaderInfo.addEventListener(Event.COMPLETE, completeFun);
            num++
        }
        private function completeFun(e:Event){
            emptyMc.addChildAt(loader,emptyMc.numChildren)
            if(emptyMc.numChildren>=2){
                emptyMc.removeChildAt(0)
            }
            trace(emptyMc.numChildren)
        }
    }

}