Egret）获取所有子元素显示对象，包括子元素的子元素

public getAllChildNum2(_dis): number {//            console.log(egret.getQualifiedClassName(_dis));            if(egret.is(_dis, "egret.DisplayObjectContainer") == false) {                return 0;            }            var childNum = _dis.numChildren;            for(var i: number = 0;i < _dis.numChildren;i++) {                childNum += this.getAllChildNum2(_dis.getChildAt(i));            }            return childNum;        }