flash 图片循环代码应该如何写，特急

stage.scaleMode=StageScaleMode.NO_SCALE;
var loader:Loader;
var urlloader:URLLoader;
var xml:XML;
var xmllist:XMLList;
var _request:URLRequest;
var total:int,num:int=0;
var fadeTween:Tween;

import fl.transitions.*;
import fl.transitions.easing.*;
urlloader=new URLLoader();
urlloader.load(new URLRequest("xml/xc.xml"));
urlloader.addEventListener(Event.COMPLETE,comp);
    function comp(event:Event):void
    {
        xml=XML(event.target.data);
        xmllist=xml.children();
        total=xmllist.length();
        //trace(xmllist[1].attribute("source"));
        var pic:String=xmllist[0].attribute("source")
        loader=new Loader();
        loader.load(new URLRequest(pic));
        addChild(loader);
    }
var tt:Timer=new Timer(3000);
tt.addEventListener(TimerEvent.TIMER,gx);
tt.start();
    function gx(e:TimerEvent):void
    {
        num++;
        if (num>=total) {
            num=0;
        }
        loader = new Loader();
        loader.load(new URLRequest(xmllist[num].attribute("source")));
        addChild(loader);
        fadeTween = new Tween(loader,"alpha",null,0,1,1,true);
    }