从NSDateComponents创建的NSDate不正确？

Question

I created an NSDate by dateFromComponents , using NSCalendar with NSGregorianCalendar identifier, here's the strange part: The date get incorrect if it's before a certain point in time before 1900/12/31

NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
NSDateComponents *components = [[NSDateComponents alloc] init];
components.year = 1900; components.month = 12; components.day = 31;
NSDate *date = [calendar dateFromComponents:components];

components.year = 1901; components.month = 1; components.day = 1;
NSDate *date2 = [calendar dateFromComponents:components];

NSLog(@"%@",calendar.timeZone.description); 
NSLog(@"%@",date);
NSLog(@"%@",date2);

The log will be:

2016-05-25 14:58:21.014 date[79754:2192157] Asia/Shanghai (GMT+8) offset 28800
2016-05-25 14:58:21.015 date[79754:2192157] 1900-12-30 15:54:17 +0000
2016-05-25 14:58:21.015 date[79754:2192157] 1900-12-31 16:00:00 +0000

As you can see, there is a 5 minutes gap during the day. However, if I set the timeZone by [NSTimeZone timeZoneForSecondsFromGMT:] , even with the same seconds deviation - 28800, it will be normal. What is the cause of this?

Answer 1

Interesting question. What you are seeing is the effects of a time zone change from Local Mean Time to China Standard Time on 01-01-1901 when the clocks were turned back 05m43s.

More details here .

Answer 2

No, the date isn't incorrect. Instead, the NSCalendar code knows things about calendars that you wouldn't dream about, like calendars changing their time offsets at some points in time in the past.

You asked for the Asia/Shanghai calendar to convert two dates, one on the day before they changed their time zone, one on the day after they changed their time zone, and both times are converted correctly. That night everyone in Shanghai had to adjust their watches.

Answer 3

Try this!!

NSCalendar *calendar = [NSCalendar currentCalendar];

NSDateComponents *components = [[NSDateComponents alloc] init];

[components setYear:1987];
[components setMonth:3];
[components setDay:17];
[components setHour:14];
[components setMinute:20];
[components setSecond:0];

NSDate *date = [calendar dateFromComponents:components];

Hope this Help:)