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
});
});
2.异步延时调用
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(.1f * NSEC_PER_SEC)), dispatch_get_global_queue(0,0), ^{
});
