IOS关于大型网站抢购、距活动结束，剩余时间倒计时的实现代码，代码比较简单，大家根据需求适当的添加修改删除代码

1.定义4个 Label 来接收倒计时:

@property (weak, nonatomic) IBOutlet UILabel *dayLabel;
@property (weak, nonatomic) IBOutlet UILabel *hourLabel;
@property (weak, nonatomic) IBOutlet UILabel *minuteLabel;
@property (weak, nonatomic) IBOutlet UILabel *secondLabel;

2.在实现文件中实现方法:

//时间戳转换为日期格式(毫秒的时间戳)
- (NSString *)timeWithTimeIntervalString:(NSString *)timeString
{
  // 格式化时间
  NSDateFormatter* formatter = [[NSDateFormatter alloc] init];
  formatter.timeZone = [NSTimeZone timeZoneWithName:@"shanghai"];
  [formatter setDateStyle:NSDateFormatterMediumStyle];
  [formatter setTimeStyle:NSDateFormatterShortStyle];
  [formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

  // 毫秒值转化为秒
  NSDate* date = [NSDate dateWithTimeIntervalSince1970:[timeString doubleValue]/ 1000.0];
  NSString* dateString = [formatter stringFromDate:date];
  NSLog(@"时间 === %@",dateString);
  return dateString;
}
-(void)downSecondHandle:(NSString *)aTimeString{

  NSDateFormatter *dateFormatter=[[NSDateFormatter alloc] init];
  [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];


  NSDate *endDate = [dateFormatter dateFromString:[self timeWithTimeIntervalString:aTimeString]]; //结束时间
  NSDate *endDate_tomorrow = [[NSDate alloc] initWithTimeIntervalSinceReferenceDate:([endDate timeIntervalSinceReferenceDate])];
  NSDate *startDate = [NSDate date];
    NSString* dateString = [dateFormatter stringFromDate:startDate];
  NSLog(@"现在的时间 === %@",dateString);
  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(), ^{
            self.dayLabel.text = @"";
            self.hourLabel.text = @"00";
            self.minuteLabel.text = @"00";
            self.secondLabel.text = @"00";
          });
        }else{
          int days = (int)(timeout/(3600*24));
          if (days==0) {
            self.dayLabel.text = @"";
          }
          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(), ^{
            if (days==0) {
              self.dayLabel.text = @"0天";
            }else{
              self.dayLabel.text = [NSString stringWithFormat:@"%d天",days];
            }
            if (hours<10) {
              self.hourLabel.text = [NSString stringWithFormat:@"0%d",hours];
            }else{
              self.hourLabel.text = [NSString stringWithFormat:@"%d",hours];
            }
            if (minute<10) {
              self.minuteLabel.text = [NSString stringWithFormat:@"0%d",minute];
            }else{
              self.minuteLabel.text = [NSString stringWithFormat:@"%d",minute];
            }
            if (second<10) {
              self.secondLabel.text = [NSString stringWithFormat:@"0%d",second];
            }else{
              self.secondLabel.text = [NSString stringWithFormat:@"%d",second];
            }

          });
          timeout--;
        }
      });
      dispatch_resume(_timer);
    }
  }


}