as3画线程序

package {

 import flash.events.MouseEvent;
 import flash.display.Sprite;
 public class DrawDemo extends Sprite {
  private var px:Number;
  private var py:Number;
  private var isDown:Boolean=false;
  private var sprite:Sprite;
  public function DrawDemo():void {

   sprite=new Sprite();
   addChild(sprite);
   stage.addEventListener(MouseEvent.MOUSE_DOWN,downHandler);
  }
  private function downHandler(evt:MouseEvent):void {
   isDown=true;
   px=mouseX;
   py=mouseY;
   stage.addEventListener(MouseEvent.MOUSE_MOVE,moveHandler);
  }
  private function moveHandler(evt:MouseEvent):void {
   if (isDown) {
    var mx:Number=mouseX;
    var my:Number=mouseY;
    sprite.graphics.lineStyle(1,0x000000,1);
    sprite.graphics.moveTo(px,py);
    sprite.graphics.lineTo(mx,my);
    sprite.graphics.endFill();
   }
   stage.addEventListener(MouseEvent.MOUSE_OUT,outHandler);
  }
  private function outHandler(evt:MouseEvent):void {
   isDown=false;
   stage.removeEventListener(MouseEvent.MOUSE_MOVE,moveHandler);
  }
 }
}