recycleview瀑布流下拉刷新后页面看不到，往上推一下才出来
when stack trace has "on a null object reference" letter a will retrace from mapping file
recycleview瀑布流下拉刷新后页面看不到，往上推一下才出来
when stack trace has "on a null object reference" letter a will retrace from mapping file