UIWindowScene and State Restoration for iOS

Why is userActivity or stateRestorationActivity property nil after I restart my app?

For state restoration of a scene session, you need to assign a NSUserActivity to the correct UIWindowScene property with your view controller's viewWillAppear method, then in the viewWillDisappear assign nil to that property.

Make sure to assign it to the UIViewController that is the rootViewController for the UIWindow being shown. Meaning, if you have a UINavigationController as the parent, use navigationController?.view.window?.windowScene?.userActivity.

A code example is available, not mine, but a helpful one.

It seems like the state restoration subsystem takes the user activity from any view controllers of active scenes and stores the state from it, which makes sense.

Other notes:

• Make sure to store your information in NSUserActivity.userInfo.
• For macOS apps, make sure you don’t restart the app too quickly, since apps may linger in the background before their process is terminated. Use the Activity Monitor to make sure the process is terminated before you restart.