时间戳

 //剩余时间可能出现null的格式 运行的时候会出错 所以要把这样的信息过滤
    if([expireDatetime isKindOfClass:[NSNull class]])
    {
        self.timeLabel.text = @"剩余:00:00:00";
    }
    else
    {
        //定义时间戳样式
        NSDateFormatter * formatter = [[NSDateFormatter alloc]init];
        formatter.dateFormat = @"yyyy-MM-dd HH:mm:ss.0";
        //结束时间
        NSDate * endDate = [formatter dateFromString:expireDatetime];
        //获取剩余时间
        NSTimeInterval interval = [endDate timeIntervalSinceNow];
        //获取时分秒
        int HH = (int)interval / 3600;
        int MM = (int)interval / 60 % 60;
        int SS = (int)interval % 60;
        
        if(HH < 0 || MM < 0 || SS < 0)
        {
            self.timeLabel.text = @"剩余:00:00:00";
        }
        else
        {
            self.timeLabel.text = [NSString stringWithFormat:@"剩余:%.2d:%.2d:%.2d",HH,MM,SS];
        }
    }