I am creating my app with Xcode 6 and it works fine on ios8. I just tested the app on ios7 and i get this error:

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '+[NSCalendar calendarWithIdentifier:]: unrecognized selector sent to class 0x3a78418c

This is the code i am using as part of converting dates from Gregorian calendar to Persian Calendar:

NSCalendar *calendar = [NSCalendar calendarWithIdentifier:@"persian"];