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iPhone - Correct way for getting current date and time for a given place / timezone and compare it with another date/time in the same place

Asked 2011-09-09T13:16:24.723
17

I'm searching the correct way to get the actual date and time for a given place / timezone, and being able to compare it to a given date/time for that same place.

Let's say, for the example, Paris, that is GMT +1. As we now, Paris can also be GMT+2 because of daylight saving, but it's part of an exception as far as I know so it must be taken in account into the answer, but not taken as a general param. The important words here are "given place".

So, if I want to know what date and time it is at Sidney Australia, or Paris France, and get that date into an NSDate for being able to compare it with another NSDate that would represent another date/time in the same place, how may I do ?

I've read pages and pages of questions and answers with comments, even on accepted answer, that says from experienced users : not a good answer -1, wrong, not the correct way of doing this, absolutely wrong, ...

So, do you know the correct real way to do that ?

In a perfect world, that date/time would be absolute even if the user's phone is not at the good time and/or date and/or timezone, or anything that can be near that perfection without needing for that to connect to a date/time server.

iphone ios cocoa-touch datetime timezone
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1 Answer

9

Use NSCalendar, and the setTimeZone method.

NSDate *newDate;
NSDateComponents *dateComponents = [[NSCalendar currentCalendar] components:~ NSTimeZoneCalendarUnit fromDate:[NSDate date]];

newDate = [[NSCalendar currentCalendar] dateFromComponents:dateComponents];
NSLog(@"newDate: %@", newDate);
NSLog(@"newDate: %.0f", [newDate timeIntervalSinceReferenceDate]);

newDate: 2011-09-09 15:02:09 +0000
newDate: 337273330

[dateComponents setTimeZone:[NSTimeZone timeZoneWithName:@"Australia/Sydney"]];
newDate = [[NSCalendar currentCalendar] dateFromComponents:dateComponents];
NSLog(@"newDate: %@", newDate);
NSLog(@"newDate: %.0f", [newDate timeIntervalSinceReferenceDate]);

newDate: 2011-09-09 00:52:03 +0000
newTimeInterval: 337222930

[dateComponents setTimeZone:[NSTimeZone timeZoneWithName:@"Europe/Paris"]];
newDate = [[NSCalendar currentCalendar] dateFromComponents:dateComponents];
NSLog(@"newDate: %@", newDate);
NSLog(@"newDate: %.0f", [newDate timeIntervalSinceReferenceDate]);

newDate: 2011-09-09 08:52:03 +0000
newTimeInterval: 337251730

answered 2011-09-09T13:36:47.237

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