ActionScript 3.0拖动物体中startDrag（）会重绘Sprite

import flash.events.Event;
import flash.events.MouseEvent;
import flash.display.Sprite;

//听说shape比sprite节省资源
var circle:Sprite=new Sprite();
circle.graphics.beginFill(0);
//试着把circle.graphics.drawCircle(100,100,10)发现每次偏移，说明每次startDrag（）方法会重绘
circle.graphics.drawCircle(0,0,10);
circle.graphics.endFill();
stage.addChild(circle);
circle.addEventListener(MouseEvent.MOUSE_DOWN,startdrag);
circle.addEventListener(MouseEvent.MOUSE_UP,stopdrag);

function startdrag(e:MouseEvent):void{
     circle.startDrag(true);
 }
function stopdrag(e:MouseEvent):void{
     circle.stopDrag();
 }