代码示例 简单粗暴 直接用就可以了 :)

- (void)startTime:(UIButton *)button
{
    __block int timeout = 60; //倒计时时间
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_source_t timeNew = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    dispatch_source_set_timer(timeNew, dispatch_walltime(NULL, 0), 1.0 * NSEC_PER_SEC, 0); //每秒执行
    dispatch_source_set_event_handler(timeNew, ^{
        if (timeout <= 0) { //倒计时结束，关闭
            dispatch_source_cancel(timeNew);
            dispatch_async(dispatch_get_main_queue(), ^{
                [button setTitle:@"获取验证码" forState:UIControlStateNormal];
                button.userInteractionEnabled = YES;
                button.backgroundColor = [UIColor colorWithRed:44/256.0 green:136/256.0 blue:242/256.0 alpha:1];
                
            });
        } else {
            NSString *strTime = [NSString stringWithFormat:@"%.2d", timeout];
            dispatch_async(dispatch_get_main_queue(), ^{
                [button setTitle:[NSString stringWithFormat:@"获取验证码(%@)", strTime] forState:UIControlStateNormal];
                button.userInteractionEnabled = NO;
            });
            timeout--;
        }
    });
    dispatch_resume(timeNew);
}