NSDateComponents将UTC日期转换为本地时区，搞乱了“今天”nsdate比较

Question

我试图使用NSDateComponents来测试动态日期是否发生“今天”。我用它来提取年/月/日，然后比较两个NSDates的值。理论上这应该起作用。我在东海岸，所以从UTC UTC-5。

当前时刻：12时四十分53秒，EST

这里是正确的NSDates，在UTC。时代在正确的UTC：

• 电流[NSDate的日期]：2016年1月19日十七点40分53秒+0000
• 活动的NSDate：2016年1月19日00:00:00 +0000

这是我的日志，显示每个日期。它将日期转换为当地时区2016-01-19 07:00:00。由于当前日期处于当天的中间位置，因此-5小时的偏移量不会导致它转换几天。然而，午夜人却转移到了一天。我怎样才能得到它尊重UTC？

的NSLog：

2016-1-19 12:40:53 (America/New_York (EST) offset -18000), 
2016-1-18 19:0:0 (America/New_York (EST) offset -18000) 

代码：

NSDateComponents *current = [[NSCalendar currentCalendar] components:NSCalendarUnitEra | NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay |NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond |NSCalendarUnitTimeZone fromDate:_date]; 
NSDateComponents *activity = [[NSCalendar currentCalendar] components:NSCalendarUnitEra | NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay |NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond |NSCalendarUnitTimeZone fromDate:activityModel.date]; 

// attempt to set timezones to UTC manually, doesn't change anything 
activity.calendar = [NSCalendar currentCalendar]; 
activity.calendar.timeZone = [NSTimeZone timeZoneWithAbbreviation:@"UTC"]; 

current.calendar = [NSCalendar currentCalendar]; 
current.calendar.timeZone = [NSTimeZone timeZoneWithAbbreviation:@"UTC"]; 


NSLog(@"%ld-%ld-%ld %ld:%ld:%ld (%@), %ld-%ld-%ld %ld:%ld:%ld (%@)", (long)[current year],(long)[current month], (long)[current day], (long)[current hour], (long)[current minute], (long)[current second], [current timeZone].description, (long)[activity year], (long)[activity month], (long)[activity day],(long)[activity hour], (long)[activity minute], (long)[activity second],[current timeZone].description); 

if([current day] == [activity day] && 
      [current month] == [activity month] && 
      [current year] == [activity year] && 
      [current era] == [activity era]) { 

      // do something if activity on current day 
} 

Answer 1

您正在改变NSDateComponents的时区。但是你要更改日历的时区调用components（或者叫NSCalendar天检查程序）之前，例如：

NSCalendar *calendar = [NSCalendar calendarWithIdentifier:NSCalendarIdentifierGregorian]; 
calendar.timeZone = [NSTimeZone timeZoneForSecondsFromGMT:0]; 

if ([calendar isDate:_date inSameDayAsDate:activityModel.date]) { 
    NSLog(@"same"); 
} else { 
    NSLog(@"diff"); 
} 

但是，如果本地时间是2016-01-19 21:00:00 -0500（即20日，UTC）。你是否想要说它和你的例子中的活动日期一样？如果是这样，那么你真的说你要使用_date本地日历，和UTC为activityModel.date，例如：

NSCalendar *calendar = [NSCalendar calendarWithIdentifier:NSCalendarIdentifierGregorian]; 

NSDateComponents *current = [calendar components:NSCalendarUnitEra | NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay |NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond |NSCalendarUnitTimeZone fromDate:_date]; 

calendar.timeZone = [NSTimeZone timeZoneForSecondsFromGMT:0]; 

NSDateComponents *activity = [calendar components:NSCalendarUnitEra | NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay |NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond |NSCalendarUnitTimeZone fromDate:activityModel.date]; 

if ([current day] == [activity day] && [current month] == [activity month] && [current year] == [activity year] && [current era] == [activity era]) { 
    NSLog(@"same"); 
} else { 
    NSLog(@"diff"); 
}