实现延迟的几种方法

1.在主线程中延迟执行某动作，不会卡主主线程，不影响后面的东做执行

dispatch_queue_t queue  = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);


dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), queue, ^{


    NSLog(@"%@", [NSThread currentThread]);

});

2.在子线程中执行某动作，不会卡主整个线程

dispatch_queue_t queue  = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);


dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), queue, ^{


    NSLog(@"%@", [NSThread currentThread]);

});

3.实现延迟，该线程本身在哪个线程中就再哪个线程中执行

NSURL *url = [NSURL URLWithString:@"http://59320.jpg.com"];

[self performSelector:@selector(download:) withObject:url afterDelay:3];

4.利用sleep实现延迟(不要用这个，会卡住主线程，即后面的动作不会执行)

[NSThread sleepForTimeInterval:3];

5.NSTimer定时器

NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:2.0 target:self  selector:@selector(delayMethod) userInfo:nil repeats:NO];

注：此方法是一种非阻塞的执行方式，
取消执行方法：- (void)invalidate;即可