iOS 主线程，执行UI刷新

主线程，执行UI刷新

dispatch_async(dispatch_get_global_queue(0, 0), ^{
      //执行耗时的异步操作..
      //................
      //................
      dispatch_async(dispatch_get_main_queue(), ^{
          //回到主线程，执行UI刷新操作
          //................
          //................
      });
  });

延时操作

 dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(10 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        //code to be executed after a specified delay code将在10后执行
 });