NSDate - Convert Date to GMT

Question

I need the ability to convert an NSDate value to a GMT Date.

How can I go about converting an NSDate value to a GMT formatted NSDate<

Answer 1

While Alex's answer was a good start, it didn't deal with DST (daylight savings time) and added an unnecessary conversion to/from the reference date. The following works for me:

To convert from a localDate to GMT, taking DST into account:

NSDate *localDate = <>
NSTimeInterval timeZoneOffset = [[NSTimeZone systemTimeZone] secondsFromGMTForDate:localDate];
NSDate *gmtDate = [localDate dateByAddingTimeInterval:-timeZoneOffset]; // NOTE the "-" sign!

To convert from a GMT date to a localDate, taking DST into account:

NSDate *gmtDate  = <>
NSTimeInterval timeZoneOffset = [[NSTimeZone systemTimeZone] secondsFromGMTForDate:gmtDate];
NSDate *localDate = [gmtDate dateByAddingTimeInterval:timeZoneOffset];

One small note: I used dateByAddingTimeInterval, which is iOS 4 only. If you are on OS 3 or earlier, use addTimerInterval.