private sumTime:number = 0;
  private countDownTime:number = 0;  
  public openView():void{
  　　this.maskImg.graphics.clear();
      //因为是从正上方开始,所以绘制的扇形一开始是-90度
      this.maskImg.graphics.drawPie(100,100,120,-90,270,"#ffffff");
      //定时器,一直绘制扇形
      Laya.timer.frameLoop(1,this,this.drawPieMask);
      this.countDownTime = 5;
      //5秒倒计时定时器
      Laya.timer.loop(1000,this,this.computeCountDownTime);
      this.timeImg.skin = "res/ui/comm/number" + this.countDownTime + ".png";
      this.sumTime = 0;
  }

   //倒计时
   private computeCountDownTime():void{
       this.countDownTime--;
       if(this.countDownTime > 0){
          this.timeImg.skin = "res/ui/comm/number" + this.countDownTime + ".png";
       }else{
          Laya.timer.clear(this,this.computeCountDownTime);
       }
   }
    
   //绘画扇形遮罩
   private drawPieMask():void{
       //计算时间
       this.sumTime += Laya.timer.delta;
       if(this.sumTime <= 5000){
           this.maskImg.graphics.clear();
           //根据时间计算扇形角度
           this.maskImg.graphics.drawPie(100,100,120,-90 + this.sumTime/5000 * 360,270,"#ffffff");
       }else{//清除定时器
           Laya.timer.clear(this,this.drawPieMask);
       }
   }