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

Question

我正在尝试使用NSDateComponents来测试动态日期是否发生在“今天”。 我用它来提取年/月/日，然后比较两个NSDate的值。 从理论上讲，这应该起作用。 我在东海岸，所以EST，UTC的时间是-5。

当前实际时间：美国东部标准时间12:40:53

这是UTC中正确的NSDate。 时间是正确的UTC：

• 当前[NSD发布日期]：2016-01-19 17:40:53 +0000
• 活动NSD发布日期：2016-01-19 00:00:00 +0000

这是我的日志，显示每个日期。 它将日期转换为本地时区2016-01-19 07:00:00。 由于当前日期是一天中的某天，因此-5小时的偏移量不会导致其偏移日期。 然而，午夜时分又回到了一天。 我如何才能尊重UTC？

NSLog的：

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

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

您正在更改NSDateComponents的时区。 但是您想在调用components （或调用NSCalendar日检查例程）之前更改日历的时区，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，如果当地时间是2016-01-19 21:00:00 -0500月19日2016-01-19 21:00:00 -0500 （即世界标准时间20号） 2016-01-19 21:00:00 -0500 。 您是否想说示例中的活动日期也是同一天？ 如果是这样，那么你真的说你要使用本地日历_date的，和UTC activityModel.date ，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");
}