Issues in converting date string (any time zone) to NSDate of French Time Zone

Question

I want to convert a date string (can be in any time zone) to a date in French Time Zone. I am using following code.

NSString * dateString = @"27/05/2015 - 19:00" // system time zone is GMT +5
NSDateFormatter* frenchDateFormatter = [[NSDateFormatter alloc] init];
[frenchDateFormatter setTimeZone:[NSTimeZone timeZoneWithName:@"Europe/Paris"]];
[frenchDateFormatter setDateFormat:@"dd/MM/yyyy - HH:mm"];
NSDate *frenchDate = [frenchDateFormatter dateFromString:dateString];
NSLog(@"%@",frenchDate);
NSString * frenchString = [frenchDateFormatter stringFromDate:frenchDate];`

Elaboration --> System time zone is GMT +5 --> French time zone is GMT +2

Date string = 27/05/2015 - 19:00

Expected result = 27/05/2015 - 16:00

Actual result (NSDate) = 2015-05-27 17:00:00 +0000

Actual result (NSString from date) = 27/05/2015 - 19:00

Kindly point out if I am missing something

Answer 1

If you use NSLog to display dates it'll be displayed in UTC. So either you have to convert in your head, or don't use it. I wrote a long answer explaining this to a different question.

Because you have set the timezone of your parsing dateFormatter to Paris the string you parse is treated as "time in paris". That's your problem, you actually wanted to parse it in local time.

The results you get are exactly as one would expect.

You create a NSDate that relates to "19:00 in Paris". Since Paris is UTC+2 that date is 17:00 in UTC (or in +0000). If you convert that date back to "time in Paris" you end up with the same string as before.

If you want to convert the representation of a point in time in your location to a different representation at a different location you have to use two dateFormatters.

NSString *localDateString = @"27/05/2015 - 19:00" // system time zone is GMT +5

NSDateFormatter* localDateFormatter = [[NSDateFormatter alloc] init];
[localDateFormatter setTimeZone:[NSTimeZone localTimeZone]];
[localDateFormatter setDateFormat:@"dd/MM/yyyy - HH:mm"];

NSDate *date = [localDateFormatter dateFromString:localDateString];       // date contains point in time. It no longer has a timezone

NSDateFormatter* franceDateFormatter = [[NSDateFormatter alloc] init];
[franceDateFormatter setTimeZone:[NSTimeZone timeZoneWithName:@"Europe/Paris"]];
[franceDateFormatter setDateFormat:@"dd/MM/yyyy - HH:mm"];

NSString * timeInFranceString = [franceDateFormatter stringFromDate:date]; // representation of the point in time from above for people in Paris