flex 画图

在FLEXBUILDER里新建一个ACTIONSCRIPT PROJECT，名字就叫flextest
建好后，把我下面的代码全部COPY覆盖到项目里的flextest.as里 ，然后RUN就可以看效果了

---------------------------flextest.as--------------------------------
package {
import flash.display.Sprite;
import flash.events.KeyboardEvent;
import flash.events.MouseEvent;

public class flextest extends Sprite
{
private var _sperite:Sprite;

public function flextest()
{

_sperite = new Sprite();//建立影片精灵
addChild(_sperite);//把精灵加入显示清单
_sperite.graphics.beginFill(0xffffff);
_sperite.graphics.drawRect(0,0,400,400);
_sperite.graphics.endFill();

_sperite.addEventListener(MouseEvent.MOUSE_DOWN,onMouseDown);
_sperite.addEventListener(MouseEvent.MOUSE_UP,onMouseUp);
}

private function onMouseDown(event:MouseEvent):void
{
_sperite.graphics.lineStyle(1,0,1);
_sperite.graphics.moveTo(mouseX,mouseY);
_sperite.addEve