在iOS中NSTimeZone的夏令时破碎了吗？

Question

I have two variables:

NSTimeZone *timeZoneMinus5 = [NSTimeZone timeZoneForSecondsFromGMT: -18000];
NSTimeZone *timeZoneEST = [NSTimeZone timeZoneWithName:@"EST"];

Tested on a device and on the simulator as well both return GMT-05:00 .

As I'm writing this the time is 2:55 am (GMT) . I am in the EST timezone so my time is 10:55pm (GMT-05:00) , observing Daylight Saving Time on April 15 2011.

However, [timeZoneEST isDaylightSavingTime] returns NO and [timeZoneEST daylightSavingTimeOffset] returns 0 .

If I use timeZoneEST to get the current time as a string:

NSDate *gmtTime = [NSDate date];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"h:mm a (z)"];
[dateFormatter setTimeZone: timeZoneEST];
NSString *timeStr = [dateFormatter stringFromDate: gmtTime];

both the simulator and the device gives me 9:55 PM (GMT-05:00) .

In my understanding I should be getting 10:55 PM (GMT-05:00) . Am I wrong or am I doing it wrong?

Answer 1

You are defining your NSTimeZone to be EST, so it makes sense that [timeZoneEST isDaylightSavingTime] returns NO . Instead use [[NSTimeZone localTimeZone] daylightSavingTimeOffset]; to get daylight saving time offset for the local time. It should return 3600 seconds.

Answer 2

You are very confused. To start with, daylight savings time in the US Eastern time zone is -4, not -5. 9:55 PM certainly is 5 hours before 2:55 am; 10:55 PM would be 4 hours before.

Chances are that "EST" is giving you exactly that: Eastern Standard Time without regard for daylight savings time. "EST5EDT" might give you the time zone you are expecting, although (assuming the device uses zoneinfo as the simulator does) "America/New_York" would be preferred.