Swift State Restoration: Bringing Your App Back to Life

Swift State Restoration: Bringing Your App Back to Life

State Restoration is a powerful tool that allows you to save and restore the state of your app. With State Restoration, your app can be brought back to life even after crashing or being killed by the system. In this article, we will explore how State Restoration works in Swift and how to implement it in your own apps.

State Restoration in Swift is based on the concept of “restorable objects”. A restorable object is an object that can be saved and restored from a previous state. The state of a restorable object is saved in a “state dictionary”, which is a dictionary containing all the information needed to restore the object. When the app is launched, the state dictionary is used to restore the state of the restorable objects.

To use State Restoration in Swift, you need to create a “Restoration Coordinator” class. This class is responsible for saving and restoring the state of the restorable objects. The Restoration Coordinator class must conform to the UIRestorationCoordinator protocol. This protocol defines several methods that are called when the state of the restorable objects needs to be saved or restored.

The first step in implementing State Restoration in Swift is to create the Restoration Coordinator class. This class should define the methods from the UIRestorationCoordinator protocol and must also have a reference to the state dictionary. The state dictionary should be initialized when the Restoration Coordinator is created and should be updated whenever the state of the restorable objects changes.

Once the Restoration Coordinator class has been created, you need to register it with the app. This can be done in the application(_:didFinishLaunchingWithOptions:) method of the AppDelegate. The Restoration Coordinator should also be registered as the restoration coordinator for the view controllers in the app. This can be done in the viewDidLoad() method of the view controller.

The next step is to create the restorable objects. Restorable objects must conform to the UIRestorableObject protocol. This protocol defines several methods that are called when the state of the object needs to be saved or restored. The state of the restorable object is stored in the state dictionary.

Once the restorable objects have been created, the next step is to implement the methods from the UIRestorableObject protocol. These methods should be used to save and restore the state of the restorable objects. For example, the saveState() method should be used to save the state of the restorable object to the state dictionary, and the restoreState() method should be used to restore the state of the object from the state dictionary.

Finally, the last step is to implement the methods from the UIRestorationCoordinator protocol. These methods should be used to save and restore the state of the restorable objects. For example, the saveState() method should be used to save the state dictionary, and the restoreState() method should be used to restore the state of the restorable objects from the state dictionary.

State Restoration is a powerful tool that can be used to bring your app back to life even after it has crashed or been killed by the system. By implementing State Restoration in Swift, you can ensure that your app’s state is always restored correctly and that users don’t lose any data when the app crashes or is killed by the system.

// Restoration Coordinator Class
class RestorationCoordinator: UIRestorationCoordinator {
    var stateDictionary: [String: Any]
    
    init(stateDictionary: [String: Any]) {
        self.stateDictionary = stateDictionary
    }
    
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey : Any]? = nil) -> Bool {
        return true
    }
    
    func viewDidLoad() {
        UIApplication.shared.registerForStateRestoration()
    }
    
    // MARK: - UIRestorableObject Protocol
    func saveState() {
        // Save state of restorable objects
    }
    
    func restoreState() {
        // Restore state of restorable objects
    }
    
    // MARK: - UIRestorationCoordinator Protocol
    func saveState(with coder: NSCoder) {
        // Save state dictionary
    }
    
    func restoreState(with coder: NSCoder) {
        // Restore state dictionary
    }
}