Flex 图片缩放、托拽效果

<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"  
    layout="absolute"     width="800" height="500" applicationComplete="app(event)" horizontalScrollPolicy="off" verticalScrollPolicy="off">
    <mx:Script>
        <![CDATA[
            import mx.controls.Alert;
            import mx.events.FlexEvent;
            protected function app(event:FlexEvent):void
            {
            img.addEventListener(MouseEvent.MOUSE_DOWN, imgMouseDown);
            img.addEventListener(MouseEvent.MOUSE_UP, imgMouseUp);
            this.addEventListener(MouseEvent.MOUSE_WHEEL, imgZoom);//滚动事件
            }
            private function imgMouseDown(evt:MouseEvent):void
            {
                evt.currentTarget.startDrag();
            }
            private function imgMouseUp(evt:MouseEvent):void
            {
                evt.currentTarget.stopDrag();
            }
            private function imgZoom(evt:MouseEvent):void
            {
                var w:Number = img.width * evt.delta * 0.02;
                var h:Number = img.height * evt.delta * 0.02;
                img.x += -w/2;
                img.y += -h/2;
                
                img.width += w;
                img.height += h;
                //Alert.show(img.width.toString());
            }
        ]]>
    </mx:Script>
    <mx:Image x="70" y="85" id="img" source="1.jpg"/>
</mx:Application>