使用GCD实现发送短信验证码效果

- (IBAction)buttonActon:(UIButton *)sender{    sender.userInteractionEnabled = NO;    // 等待的秒数    __block int count = 5;    // 获取全局队列    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);    // 实例化计时器    _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);    // 设置计时器    dispatch_source_set_timer(_timer, dispatch_walltime(NULL, 0), 1 * NSEC_PER_SEC, 0 * NSEC_PER_SEC);    // 设置计时器事件处理    dispatch_source_set_event_handler(_timer, ^{        if (count == 0) {            // 取消计时器            dispatch_source_cancel(_timer);            // 在主队列里处理            dispatch_async(dispatch_get_main_queue(), ^{                // 将按钮置为正常状态                sender.userInteractionEnabled = YES;                sender.titleLabel.font = [UIFont systemFontOfSize:15];                sender.backgroundColor = [UIColor orangeColor];                [sender setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];                [sender setTitle:@"发送验证码" forState:UIControlStateNormal];            });        }        else        {            NSString *str = [NSString stringWithFormat:@"剩余(%d)s",count];            // 在主队列里处理            dispatch_async(dispatch_get_main_queue(), ^{                // 按钮显示剩余等待时间                sender.backgroundColor = [UIColor grayColor];                [sender setTitleColor:[UIColor lightGrayColor] forState:UIControlStateNormal];                [sender setTitle:str forState:UIControlStateNormal];            });            count--;        }    });    // 开启timer    dispatch_resume(_timer);}- (void)dealloc{    // 取消计时器    if (_timer) dispatch_source_cancel(_timer);}