StateRestorationSimple

This is a simple implementation of state restoration as outlined in Preserving your app’s UI across launches.

Cross referencing to the sections in that document, I have:

“Enable state preservation and restoration for your app”

I have defined application(_:shouldSaveSecureApplicationState:) and application(_:shouldRestoreSecureApplicationState:) to both return true.
“Assign restoration identifiers to your view controllers”

I have set the restoration ID in the storyboard for the view controller.
“Encode and decode custom information for your app”

The docs say:

During the preservation process, UIKit calls the encodeRestorableState(with:) method of each preserved view and view controller.

I have implemented encodeRestorableState(with:) (making sure to call super renditions) and application(_:willEncodeRestorableStateWith:).
“Create view controllers when asked”

I don’t manually create any view controllers, as the docs say:

UIKit uses your app’s storyboards to recreate your view controllers.

It also says:

UIKit calls each view controller’s decodeRestorableState(with:) method to restore its state information.

Note: It is very important to not use UIScene related objects/methods. The above only works in non-scene based codebases.

In terms of my testing process, I do not force-quit the app. The steps I follow are:

launch the app from Xcode;
type some text in text field;
leave the app (without terminating it) … application(_:shouldSaveSecureApplicationState:) is called, but encodeRestorableState(with:) is not;
only after I am at the home screen do I hit “stop” button in Xcode; and
relaunch the app from Xcode … application(_:shouldRestoreSecureApplicationState:) is called, but decodeRestorableState(with:) is not.

robertmryan/StateRestorationSimple