Flex ActionScript实例代码之动画与速度

package
{
    import flash.display.*;
    import flash.events.Event;
    import flash.utils.getTimer;

    public class Main extends Sprite
    {
        protected const SPEED:Number = 50; //50 pixels per second
        protected var myShape:DisplayObject;
        protected var lastTime:int;

        public function Main ()
        {

        addEventListener(Event.ENTER_FRAME, onEnterFrame);
        lastTime = getTimer();
        var s:Sprite = new Sprite();
        addChild(s);
        myShape = getChildAt(0);
        }

        protected function onEnterFrame(event:Event):void
        {
           var time:int = getTimer();
            myShape.x += SPEED * (time - lastTime) / 1000;
            lastTime = time;
       }
    }
}