GCD计时DEMO

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    
    _timeBtn = [UIButton buttonWithType:UIButtonTypeCustom];
    [_timeBtn setBackgroundImage:[UIImage imageNamed:@"short2_apply_btn_disable"] forState:UIControlStateNormal];
    [_timeBtn setBackgroundImage:[UIImage imageNamed:@"short2_apply_btn_over"] forState:UIControlStateHighlighted];
    [_timeBtn setTitle:@"发送验证码" forState:UIControlStateNormal];
    _timeBtn.frame = CGRectMake(100, 100, 150, 30);
    [_timeBtn addTarget:self action:@selector(starTime) forControlEvents:UIControlEventTouchUpInside];

    [self.view addSubview:_timeBtn];
}

- (void)starTime
{
    __block NSInteger timeout = 60; // 倒计时时间
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    
    dispatch_source_set_timer(timer, DISPATCH_TIME_NOW, 1 * NSEC_PER_SEC, 0 * NSEC_PER_SEC);
    dispatch_source_set_event_handler(timer, ^{
        if (timeout <= 0 ) {
            dispatch_source_cancel(timer);
            dispatch_async(dispatch_get_main_queue(), ^{
                [_timeBtn setTitle:@"发送验证码" forState:UIControlStateNormal];
                _timeBtn.userInteractionEnabled = YES;

            });
        }else{
            NSInteger seconds = timeout % 60;
            NSString *strTime = [NSString stringWithFormat:@"%.2d",seconds];
            dispatch_async(dispatch_get_main_queue(), ^{
                NSLog(@"___%@",strTime);
                [_timeBtn setTitle:[NSString stringWithFormat:@"%@秒后重新发送",strTime] forState:UIControlStateNormal];
                _timeBtn.userInteractionEnabled = NO;
            });
        }
        timeout-- ;
    });
    dispatch_resume(timer);
}