[]对象mask的区域改变问题！

 private addedToStage():void{

        this.__mask = new Laya.Sprite();

        this.__mask.graphics.drawRect(0,0,this.img_bar.width,this.img_bar.height,"#000000");

        this.setValue(0);

       

    }

    private setValue(v:number):void{

        this.__mask.scaleX = v;

        this.img_bar.mask = null;//第二次设置mask的时候必须给原对象的mask置空,否则无效

        this.img_bar.mask = this.__mask;

        this.label_pro.text = v * 100 + "%";

    }