Actionscript 3 :: Resize DisplayObject To Fit Panel In Flex Application?

I am trying to attach some of my actionscript class, inherited from Sprite, to my Flex application by attaching it to a UIComponent, then add UIComponent to a panel. However, the size of my Sprite class appears to be larger than the panel. So, I try to resize it using DisplayObject.scale property, but I need to know the size of my container. Since I try to make my code reusable, I figure that I should let my Sprite class handle the resize by getting it via its parent property (let's say, I can resize it by set

this.scaleX = this.parent.Width/this.width or something like this)

However, my Sprite class's parent, which is the UIComponent, has width/height of 0. So, my question is:

1) Is there any better way to resize DisplayObject class to fit its container when attached to Flex object?

2) If you know, why my UIComponent's size remain 0 and my DisplayObject still appears at its full size? Here's my code, using Flash Builder 4:

private var loader:Loader = new Loader();
private function testLoader():void {
var urlRequest:URLRequest = new URLRequest("http://localhost/welcome.png");[code].......