On iOS, State Preservation and Restoration can be used to save and reload app state to make app termination appear like a temporary interruption. When an apps state is restored, the app returns the user to the last point of use so that the user can continue with whatever task was in progress.
iOS Programming Guide - State Preservation and Restoration:
The state preservation system in UIKit provides a simple but flexible infrastructure for preserving and restoring the state of your app’s view controllers and views. The job of the infrastructure is to drive the preservation and restoration processes at the appropriate times. To do that, UIKit needs help from your app. Only you understand the content of your app, and so only you can write the code needed to save and restore that content. And when you update your app’s UI, only you know how to map older preserved content to the newer objects in your interface.
