延迟调用

//    [self performSelector:@selector(play:) withObject:self afterDelay:3];
    
//    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0*NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
//        NSLog(@"========");
//    });
    
    [NSTimer scheduledTimerWithTimeInterval:2 target:self selector:@selector(play:) userInfo:nil repeats:NO];