• (void)viewDidLoad {
  [super viewDidLoad];

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

  NSDate *endDate = [dateFormatter dateFromString:[self getyyyymmdd]];
  NSDate endDate_tomorrow = [[NSDate alloc] initWithTimeIntervalSinceReferenceDate:([endDate timeIntervalSinceReferenceDate] + 243600)];
  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(), ^{
                    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);
    }
  

  }
  }

-(NSString *)getyyyymmdd{
NSDate *now = [NSDate date];
NSDateFormatter *formatDay = [[NSDateFormatter alloc] init];
formatDay.dateFormat = @"yyyy-MM-dd";
NSString *dayStr = [formatDay stringFromDate:now];

return dayStr;

}