Maintain Compatibility with iOS11 in 2020

It CAN be done

Difficulty: Beginner | Easy | Normal | Challenging
This article has been developed using Xcode 11.4.1, and Swift 5.2.2

The example

I'm going to get rid of the Storyboard as I work like that here's how to do it. Sorry.

I'm going to have an initial view controller that just displays an image of Golshifteh Farahani. Sorry for lack of originality.

The Scene Delegate (iOS 13+)

We are going to need to launch the InitialViewController. This reqyures replacing

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        // Use this method to optionally configure and attach the UIWindow `window` to the provided UIWindowScene `scene`.
        // If using a storyboard, the `window` property will automatically be initialized and attached to the scene.
        // This delegate does not imply the connecting scene or session are new (see `application:configurationForConnectingSceneSession` instead).
        guard let _ = (scene as? UIWindowScene) else { return }
    }

with

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        guard let windowScene = (scene as? UIWindowScene) else { return }
        window = UIWindow(frame: windowScene.coordinateSpace.bounds)
        window?.windowScene = windowScene
        self.window?.rootViewController = InitialViewController()
        window?.makeKeyAndVisible()
    }

but of course we will also need an instance variable to hold the reference for the window.

var window: UIWindow?

But what about iOS11?

If we change the deployment target in the project

which then allows you to choose iOS11 simulators (as long as you have them added in Xcode.

Then...

Oh dear!

So we need to work through the App delegate!

The Aoo Delegate

We are going ahead to fix those errors.

We add a property for UIWindow:

    var window: UIWindow?

and change the func application(application: didFinishLaunchingWithOptions:) -> Bool function to

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
     if #available(iOS 13.0, *) {
        // move to SceneDelegate
    } else {
        // Support for iOS11
        self.window = UIWindow(frame: UIScreen.main.bounds)
        self.window!.rootViewController = InitialViewController()
        self.window?.makeKeyAndVisible()
    }
    return true
}```

and both of the subsequent functions are only supported from iOS13, and need to be marked as such:

```swift
@available(iOS 13.0, *)

Fix the SceneDelegate We only wish to use the SceneDelegate if it is avaliable, so we can put the following statement @available(iOS 13.0, *) just above the SceneDelegate class declaration.

Now this works on iOS11 devices!

Conclusion

It is rather complex in the description, but rather easy in the implementation. Take a look at the attached Repo. It is a rather wonderful thing.

If you've any questions, comments or suggestions please hit me up on Twitter