CountDown.png

// 全局
{
    dispatch_source_t  _timer;
}

#pragma mark 倒计时
- (void)countdownFromTimeString:(NSString *)timeString
{
    if (!_timer) {
        // 倒计时时间
        __block int timeout = timeString?[timeString intValue]:0;
        if (timeout!=0) {
            dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
            _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0,queue);
            dispatch_source_set_timer(_timer,dispatch_walltime(NULL, 0),1.0*NSEC_PER_SEC, 0); //每秒执行
            dispatch_source_set_event_handler(_timer, ^{
                if (timeout<=0) {
                    dispatch_source_cancel(_timer);
                    _timer = nil;
                    dispatch_async(dispatch_get_main_queue(), ^{
                        _dayLabel.text = @"00";
                        _hourLabel.text = @"00";
                        _minuteLabel.text = @"00";
                        _secondLabel.text = @"00";
                    });
                }else{
                    int days = (int)(timeout/(3600*24));
                    if (days==0) {
                        _dayLabel.text = @"00";
                    }
                    int hours = (int)((timeout-days*24*3600)/3600);
                    int minute = (int)(timeout-days*24*3600-hours*3600)/60;
                    int second = timeout-days*24*3600-hours*3600-minute*60;
                    dispatch_async(dispatch_get_main_queue(), ^{
                        _dayLabel.text = [NSString stringWithFormat:@"%0*d",2, days];
                        _hourLabel.text = [NSString stringWithFormat:@"%02d", hours];
                        _minuteLabel.text = [NSString stringWithFormat:@"%02d", minute];
                        _secondLabel.text = [NSString stringWithFormat:@"%02d", second];
                    });
                    timeout--;
                }
            });
            dispatch_resume(_timer);
        }
    }
}