第四章中平铺可缩放的底纹背景问题

[whitebud]

我将该范例代码改为通过代码创建背景后，怎么不需要侦听就能出来效果呢？在代码中测试新建的背景元件的宽度为2500，这是什么原因？急盼老师以及各位高手能解释一下！代码如下，链接的图片名为pic：


Stage.align = "TL";
Stage.scaleMode = "noScale";

createEmptyMovieClip("background_mc",0);
var temp:MovieClip = background_mc.attachMovie("pic", "pic1", 0);

var tw:Number = temp._width;
var th:Number = temp._height;
var nw:Number = Math.ceil(Stage.width/tw);
var nh:Number = Math.ceil(Stage.height/th);
removeMovieClip(temp);
for (var i:Number = 0; i<tw; i++) {
for (var j:Number = 0; j<th; j++) {
var img:MovieClip = background_mc.attachMovie("pic", "pic"+i, background_mc.getNextHighestDepth());
img._x = tw*i;
img._y = th*j;
}
}
trace(background_mc._width)