The right place to call .removeObserver for NSNotificationCenter = Swift deinit()?

Question

I've read a lot of suggestions for the right place to call .removeObserver for NSNotificationCenter since viewDidUnload is not an option.

I was just wondering if the new deinit() in Swift would be a good choice?

-nick

Answer 1

It really depends on the role of the class where you subscribe to NSNotificationCenter notifications. If you are subscribing in:

UIView

Then you should unsubscribe as soon as view gets invisible to the user. To save CPU cycles and not consume resources while user does not see the view.

UIViewController

Here it also depends on kind of action that you are going to perform in response to notification. If it is just a UI adjustment that you should unsubscribe as soon as view controller disappears from the screen.

You App Service layer

Here it is OK to have .removeObserver inside deinit(). however even here I tend to suggest you to be more explicit about when you subscribe and unsubscribe from NSNotificationCenternotifications and put them in start and stop methods of your service.

Answer 2

If you were previously calling removeObserver in viewDidUnload/dealloc/deinit, then starting with iOS 9.0 and macOS 10.11, you don't need to call it anymore:

If your app targets iOS 9.0 and later or macOS 10.11 and later, you don't need to unregister an observer in its dealloc method.

source: https://developer.apple.com/documentation/foundation/notificationcenter/1413994-removeobserver