下面加粗的两行，原意应该是利用删除的item，但是看定义arr上面定义的是局部变量。
__proto._createItems = function (startY, numX, numY) {
		var box = this._content;
		var cell = this._getOneCell();
		var cellWidth = cell.width + this._spaceX;
		var cellHeight = cell.height + this._spaceY;
		if (this.cacheContent) {
			var cacheBox = new Box();
			cacheBox.cacheAsBitmap = true;
			cacheBox.pos((this._isVertical ? 0 : startY) * cellWidth, (this._isVertical ? startY : 0) * cellHeight);
			this._content.addChild(cacheBox);
			this._content.optimizeScrollRect = true;
			box = cacheBox;
		} else {
			var arr = [];
			for (var i = this._cells.length - 1; i > -1; i--) {
				var item = this._cells[i];
				item.removeSelf();
				arr.push(item);
			}
			this._cells.length = 0;
		}
		for (var k = startY; k < numY; k++) {
			for (var l = 0; l < numX; l++) {
				if (arr && arr.length) {
					cell = arr.pop();
				} else {
					cell = this.createItem();
				}
				cell.x = (this._isVertical ? l : k) * cellWidth - box.x;
				cell.y = (this._isVertical ? k : l) * cellHeight - box.y;
				cell.name = "item" + (k * numX + l);
				box.addChild(cell);
				this.addCell(cell);
			}
		}
	}