Question

I am loading in dates from my web service, I’m sending dates in the format (GMT times): 02/11/11 10:56:09

I am creating an NSDate form this using NSDateFormatter as such:

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"dd/MM/yyyy HH:mm:ss"];
NSDate *journeyDate = [dateFormatter dateFromString:str];
[dateFormatter release];

This works great, after I’m comparing this to the current date to get relative time intervals.

The problem is when the phone is set up in a different timezone, when I load in the date from my api, and use the date formatter, what seems to be happening is the phone is assuming the date string is local time and it’s converting it to GMT.

Example:

I load in a date with the time 10am from the api.
The phone is set to PDT.
The date formatter is creating an NSDate assuming that my date string with 10am, is actually relevant to the phone.

I end up with a date and time equal to 5pm, adding 10 hours.

I am trying to specify in my date formatter that the string is GMT, but I’m having trouble, I’ve tried the following, adding GMT to the format:

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"dd/MM/yyyy HH:mm:ss GMT"];
NSDate *journeyDate = [dateFormatter dateFromString:str];
[dateFormatter release];

This is not working.

Can anyone give any advice ?

Solution

Just a recap, I got it working with a terrible work around by appending GMT to the original string, and formatting that:

NSString * cheat = [NSString stringWithFormat:@"%@ GMT", str];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"dd/MM/yyyy HH:mm:ss zzzz"];
NSDate *journeyDate = [dateFormatter dateFromString:cheat];
[dateFormatter release];
return journeyDate;

This was a kind of unstable hack, because if the string changed to include a timezone, it wouldn’t work anymore. For anyone who needs to do as myself, the following is just a quick example on how to create an NSTimeZone.

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"dd/MM/yyyy HH:mm:ss"];
[dateFormatter setTimeZone:[NSTimeZone timeZoneWithName:@"UTC"]];
NSDate *journeyDate = [dateFormatter dateFromString:str];
[dateFormatter release];
return journeyDate;

Thanks for the quick help.

Answer 1

I suspect you just want to use NSDateFormatter.setTimeZone to force it to use UTC. You don’t want to change the format string because presumably the string doesn’t include the letters “GMT” – instead, you want to change which time zone the string is interpreted in, which is what setTimeZone will do.