//当前日前日期

    NSDate *today = [NSDate date];

    //时区

    NSTimeZone *zone = [NSTimeZone systemTimeZone];

    //设置间隔

    _interval = [zone secondsFromGMTForDate: today];

    //今天+8小时（中国上海时区）

    today = [today  dateByAddingTimeInterval: _interval];

    //获取明天日期

    NSDate *tomorrowDate = [[NSDate alloc]initWithTimeInterval:24 * 60 * 60 sinceDate:[NSDate date]];

    //日历 

   NSCalendar *calendar = [NSCalendar currentCalendar];

   //comps里可以分离出时间年月日等信息

NSDateComponents *comps = [calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSWeekCalendarUnit | NSWeekdayCalendarUnit |NSWeekdayOrdinalCalendarUnit | NSHourCalendarUnit) fromDate:tomorrowDate];

   //获取当前星期几   

    NSInteger weekday = [comps weekday];

  //将NSString类型转换成NSDate    

    NSDate *serverDate = [dateFomatter dateFromString:serverTimeStr];

    NSDate *createDate = [dateFomatter dateFromString:createTimeStr];

 

    //算出两个Date的间隔

   NSTimeInterval betweenTime = [serverDate timeIntervalSinceDate:createDate];