Difference between NSCalendarUnitWeekOfYear & NSCalendarUnitWeekOfMonth

Question

I want to make a UILocalNotification repeat every week, before iOS7 I would use localNotification.repeatInterval = NSWeekCalendarUnit - except

Answer 1

As for the UILocalNotification

NSCalendarUnitWeekOfYear should be used as a unit for repeatInterval.

When I set repeatInterval = NSCalendarUnitWeekOfMonth for the notification scheduled 10 seconds from now, the notification doesn't fire, and the description of the instance of UILocalNotification prints .. next fire date = (null) ...

If I use NSCalendarUnitWeekOfYear then notification appears and I see correct next fire date from code in the notification's description.