如何创建可拖动的mc?

如何创建可拖动的mc?下面就来看看利用as 3.0 创建可拖动的mc的一代码,注明本文来自网络.

package com.sxl001{
import .display.Sprite;
import flash.events.MouseEvent;
public class DragMc extends Sprite {
private var circle:Sprite;
private var begin:Boolean;
private var dx:Number;//用于计算MouseX与圆的x位置差的变量
private var dy:Number;//用于计算MouseY与圆的y位置差
public function DragMc() {
begin=false;
init();
}
private function init() {
circle=new Sprite();
addChild(circle);
circle.graphics.beginFill(0xFF0000);
circle.graphics.drawCircle(0,0,20);
circle.graphics.endFill();
circle.x=stage.stageWidth/2-circle.width/2;
circle.y=stage.stageHeight/2-circle.height/2;
circle.addEventListener(MouseEvent.MOUSE_DOWN,onMD);
circle.addEventListener(MouseEvent.MOUSE_MOVE,onMM);
circle.addEventListener(MouseEvent.MOUSE_UP,onMU);
}
private function onMD(ev:MouseEvent) {
dx=stage.mouseX-circle.x;//计算MouseX与圆的x位置差
dy=stage.mouseY-circle.y;//计算MouseY与圆的y位置差
begin=true;
}
private function onMM(ev:MouseEvent) {
if (begin) {//圆跟随Mouse
circle.x=stage.mouseX-dx;
circle.y=stage.mouseY-dy;
}
}
private function onMU(ev:MouseEvent) {
begin=false;
}
}
}