最近的项目中需要在自定义的Cell中用到活动结束倒计时，所以整理出来在这里：
在自定义的Cell.h文件中

@property (nonatomic, strong) dispatch_source_t timer;
@property (notatomic, string) NSString *endDate;  //结束的时间

在cell.m文件中

- (void)setEndDate:(NSString *)endDate
{
        _endDate = endDate;
         [self downSecondHandle:_endDate];
}

-(void)downSecondHandle:(NSString *)endDateString{
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

    NSDate *endDate = [NSDate dateWithFormat:endDateString]; 
    NSDate *endDate_tomorrow = [[NSDate alloc] initWithTimeIntervalSinceReferenceDate:([endDate timeIntervalSinceReferenceDate])];
    NSDate *startDate = [NSDate date];
    NSTimeInterval timeInterval =[endDate_tomorrow timeIntervalSinceDate:startDate];

    if (_timer==nil) {
        __block int timeout = timeInterval; //倒计时时间

        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){ //倒计时结束，关闭
                    dispatch_source_cancel(_timer);
                    _timer = nil;
                    dispatch_async(dispatch_get_main_queue(), ^{
                        //倒计时结束的时候更新UI
                    });
                }else{
                    int days = (int)(timeout/(3600*24));
                    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(), ^{
                        NSLog(@"-->剩余时间:%d天%d时%d分%d秒",days,hours,minute,second);
                       self.downSecond.text = [NSString stringWithFormat:@"剩余:%d天%d时%d分%d秒",days,hours,minute,second];
                    });
                    timeout--;
                }
            });
            dispatch_resume(_timer);
        }
    }
}