NSDateComponents keep changing the GMT? - objective-c

Question

This might be basic but i couldn't find a similar problem to clearly understand that.
I have some date which is this :
2015-07-19 12:00:00 +0000
then i am taking this date and try to get the hour of it with :
NSCalendar *gregorianCalendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
NSDateComponents *components = [gregorianCalendar components:NSCalendarUnitDay | NSCalendarUnitHour |NSCalendarUnitMinute | NSCalendarUnitMonth | NSCalendarUnitYear| NSCalendarUnitWeekday fromDate:tdate];
long hour=[components hour];
NSLog(#"-- %ld ",hour); //gives 15
Then i get the hour as 15 and not 12 as the original date .
The 3 hours different is i guess my GMT +3 .
How can i get 12 - the original date hour ?
adding this
[components setTimeZone:[NSTimeZone timeZoneWithAbbreviation:#"GMT"]];
didn't helped.
When i create that original date with components class, i do it in the exact way that i later do it again, so there shouldn't be any change in the GMT times.
To create the original date i do :
NSDateComponents *components = [[NSCalendar currentCalendar] components:NSCalendarUnitDay |NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitWeekday | NSCalendarUnitHour | NSCalendarUnitMinute fromDate:new];
[components setHour:12];
So, why when you extract it in the exact same way you dont get the same result ?
thanks .

Answer 1

When Using NSCalender and NSDateCompoment it will always translate date to your systemDate. If you want to have that Date invariant and meanwhile use DateCompoment to access components you need to remove the timeInterval between your systemeData to that date system(GMT in your case).
NSTimeZone* currentTimeZone = [NSTimeZone localTimeZone];
NSTimeInterval timeDiff = [currentTimeZone secondsFromGMTForDate:aGMTDate];
NSDate *gmtDate = [[NSDate alloc] initWithTimeInterval:(-timeDiff) sinceDate:[NSDate date]];