A Complete Guide To App State Restoration in iOS | Technical Blog | Yudiz
App State restoration is for the user to come back to the app as they left it last time before it is a suspended app. Returning an app to its previous app state offers a better user experience and saves time for the user.
The system automatically deletes an app’s preserved state when the user force quits the app. Deleting the preserved state information when the app is killed is a safety precaution. (As a safety precaution, the system also deletes preserved state if the app crashes twice during launch.) If you want to test your app’s ability to restore its state, you should not use the multitasking bar to kill the app during debugging. Instead, use Xcode to kill the app or kill the app programmatically by installing a temporary command or gesture to call exit on demand.
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