flex图片移动不流畅

我写了一个图片移动，但是移动时图片抖动很厉害，鼠标也会跑出图片
XML code:
<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" creationComplete="init()">
<mx:Script>
<![CDATA[
import mx.controls.Alert;

private var _x:int;
private var _y:int;
private var _tempX:Number;
private var _tempY:Number;
private var isDown:Boolean;
private function init():void {
//can1.addEventListener(MouseEvent.CLICK,moveDown);
isDown = false;
myMove.duration = 100;
//img.addEventListener(MouseEvent.CLICK,mouseClick);
img.addEventListener(MouseEvent.MOUSE_DOWN,mouseDown);
img.addEventListener(MouseEvent.MOUSE_MOVE,mouseMove);
img.addEventListener(MouseEvent.MOUSE_UP,mouseUp);
img.addEventListener(MouseEvent.MOUSE_OUT,mouseOut);
}
private function mouseClick(e:MouseEvent):void {
Alert.show(img.x+'\t'+img.y,'aaa');
}
private function mouseDown(e:MouseEvent):void {
isDown = true;
_tempX = img.mouseX;