1.nstimer
可取消
[NSTimer scheduledTimerWithTimeInterval:1/30.0f repeats:true block:^(NSTimer * _Nonnull timer) {
//代码
}];
- dispatch
多线程延迟，缺点->无法取消
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, delayTime * NSEC_PER_SEC), dispatch_get_main_queue(), block);
