iOS 時間類常用方法

//當前日前日期

    NSDate *today = [NSDate date];

    //時區

    NSTimeZone *zone = [NSTimeZone systemTimeZone];

    //設置間隔

    _interval = [zone secondsFromGMTForDate: today];

    //今天+8小時（中國上海時區）

    today = [today  dateByAddingTimeInterval: _interval];

    //獲取明天日期

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

    //日歷 

   NSCalendar *calendar = [NSCalendar currentCalendar];

   //comps里可以分離出時間年月日等信息

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

   //獲取當前星期幾   

    NSInteger weekday = [comps weekday];

  //將NSString類型轉換成NSDate    

    NSDate *serverDate = [dateFomatter dateFromString:serverTimeStr];

    NSDate *createDate = [dateFomatter dateFromString:createTimeStr];

    //算出兩個Date的間隔

   NSTimeInterval betweenTime = [serverDate timeIntervalSinceDate:createDate];