UIViewController State Restoration - weak relationships

Question

With iOS 6 Apple added state restoration to UIViewController and related classes. This allows the application to save state when terminated and restore it when the user resumes the application.

Everything seems to work fine, however I have reached a weird scenario which doesn't want to fit into the pattern.

Let's assume we have two view controllers, ViewControllerOne and ViewControllerTwo, both of them store some arbitrary state that is restored successfully. Now let's imagine that ViewControllerOne has a delegate property and that ViewControllerTwo is that delegate (which is a common pattern for modal view controllers). Who is responsible for restoring this relationship? And how is it supposed to be stored/restored?

In my particular case no storyboards are involved, the restoration happens in code, via the restorationClass property. My first instinct was to try and restore the relationship whilst creating the view controller in the restorationClass, however as the restorationClass has no idea of other existing controllers it can't quite restore such a relationship.

Alternatively, if it is the view controller that declares the delegate property, that is supposed to restore the relationship, then how does it now of the controller instance that was restored in some other class?

In short, this seems like a poorly documented scenario and I was hoping someone could shed some light on it.

Answer 1

I would say, the task falls on the delegate view controller to set itself as such, just like you do it before pushing the other view controller.

On how you can accomplish this, you have several options.

You can store a weak reference to your view controllers in a globally accessible location (for example, the app delegate), and use these values in application:didDecodeRestorableStateWithCoder: to set the delegation - this is what this method is for in the API.

Alternatively, you could post a "hereIAmThisIsMe" notification (with self part of the user info) from the top view controller to which the delegate listens and sets itself as a delegate.