NSDateComponents將UTC日期轉換爲本地時區，搞亂了「今天」nsdate比較

Question

我試圖使用NSDateComponents來測試動態日期是否發生「今天」。我用它來提取年/月/日，然後比較兩個NSDates的值。理論上這應該起作用。我在東海岸，所以從UTC UTC-5。

當前時刻：12時四十分53秒，EST

這裏是正確的NSDates，在UTC。時代在正確的UTC：

• 電流[NSDate的日期]：2016年1月19日十七點40分53秒+0000
• 活動的NSDate：2016年1月19日00:00:00 +0000

這是我的日誌，顯示每個日期。它將日期轉換爲當地時區2016-01-19 07:00:00。由於當前日期處於當天的中間位置，因此-5小時的偏移量不會導致它轉換幾天。然而，午夜人卻轉移到了一天。我怎樣才能得到它尊重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) 

代碼：

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

您正在改變NSDateComponents的時區。但是你要更改日曆的時區調用components（或者叫NSCalendar天檢查程序）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，如果本地時間是2016-01-19 21:00:00 -0500（即20日，UTC）。你是否想要說它和你的例子中的活動日期一樣？如果是這樣，那麼你真的說你要使用_date本地日曆，和UTC爲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"); 
}