需求：

Cell中倒计时显示，到期刷新接口，超时数据消失。后端提供订单生成时间戳createdTime。

计算：

到期时间 = 订单生成时间+后端订单预留时间
剩余时间 = 到期时间 - 现在时间
剩余时间的年,月,日,时,分,秒都小于等于0时即为超时失效。

工具使用：CountDown

//导入文件，链接文章末尾
#import "CountDown.h"
@property (nonatomic , strong) CountDown *countDown;

    //轮询初始化
    self.countDown = [[CountDown alloc] init];
    __weak __typeof(self) weakSelf= self;
    [self.countDown countDownWithPER_SECBlock:^{
        [weakSelf updateTimeInVisibleCells];
    }];

//轮询并对Cell进行赋值
- (void)updateTimeInVisibleCells{
    NSArray  *cells = self.tableView.visibleCells; //取出屏幕可见ceLl
    for (OpenCardWriteCell *cell in cells) {
        OpenCardFailedModel *model = self.dataArray[cell.tag];
        [cell.readBtn setTitle:[self getNowTimeWithString:validateString(model.createdTime)] forState:UIControlStateNormal];
    }
}

//计算时间差
- (NSString *)getNowTimeWithString:(NSString *)aTimeString{
    
    NSDate *nowDate = [NSDate dateWithTimeIntervalSinceNow:0];//获取当前时间0秒后的时间
    //30分钟后
    NSString *startStr = validateString(aTimeString);
    NSTimeInterval startTime = [startStr doubleValue]*0.001+1800;
    NSDate *detaildate = [NSDate dateWithTimeIntervalSince1970:startTime];
    //对比得到差值
    NSTimeInterval timeInterval = [detaildate timeIntervalSinceDate:nowDate];
    
    int days = (int)(timeInterval/(3600*24));
    int hours = (int)((timeInterval-days*24*3600)/3600);
    int minutes = (int)(timeInterval-days*24*3600-hours*3600)/60;
    int seconds = timeInterval-days*24*3600-hours*3600-minutes*60;
    
    //以下按自己需要使用
    NSString *dayStr;NSString *hoursStr;NSString *minutesStr;NSString *secondsStr;
    dayStr = [NSString stringWithFormat:@"%d",days];
    hoursStr = [NSString stringWithFormat:@"%d",hours];
    if(minutes<10)
        minutesStr = [NSString stringWithFormat:@"0%d",minutes];
    else
        minutesStr = [NSString stringWithFormat:@"%d",minutes];
    if(seconds < 10)
        secondsStr = [NSString stringWithFormat:@"0%d", seconds];
    else
        secondsStr = [NSString stringWithFormat:@"%d",seconds];
    if (hours<=0&&minutes<=0&&seconds<=0) {
        [self queryOrderDataMethod];
        return @"已超时";
    }
    
    if (days) {
        return [NSString stringWithFormat:@"剩余时间  %@天%@:%@:%@", dayStr,hoursStr, minutesStr,secondsStr];
    } else if(hours){
        return [NSString stringWithFormat:@"剩余时间  %@:%@:%@", hoursStr,minutesStr,secondsStr];
    }else
        return [NSString stringWithFormat:@"剩余时间  %@:%@", minutesStr,secondsStr];
}

//销毁
- (void)viewDidDisappear:(BOOL)animated{
    [super viewDidDisappear:animated];
    [_countDown destoryTimer];
}

感谢文明大佬的技术支持：CountDown

参考文章：
https://blog.csdn.net/minjing_lin/article/details/51783163
https://blog.csdn.net/m372897500/article/details/46443699
https://blog.csdn.net/bitcser/article/details/52240587