NSDateComponents将UTC日期转换为本地时区，使“今天”nsdate比较混乱

Question

我试图使用NSDateComponents来测试动态日期是否发生在“今天”。我使用它提取年/月/日，然后比较两个NSDATE的值。理论上这应该行得通。我在东海岸，所以东部时间，协调世界时-5。

当前实际时间：美国东部时间12:40:53

以下是正确的NSDATED（以UTC表示）。时间是正确的UTC：

• 当前[NSDate日期]:2016-01-19 17:40:53+0000
• 活动NSdate：2016-01-19 00:00:00+0000

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

您正在更改NSDateComponents的时区。但您希望在调用组件（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");
}

但如果当地时间是2016-01-19 21:00:00-0500（即20日，协调世界时）呢。你想让它说它和你的例子中的活动日期也是同一天吗？如果是这样，那么您实际上是说您希望对_date使用本地日历，对activitymodel.date使用UTC，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");
}