Perform segue in AppDelegate - swift

Question

When a Firebase token is invalid, I want that the user is redirect to my app loginVC. This is my code:
func userErrorLogout() {
print("user error logout")
let storyboard = UIStoryboard(name: "Main", bundle: nil);
let viewController: ViewController = storyboard.instantiateViewController(withIdentifier: "loginVC") as! ViewController;
let rootViewController = self.window!.rootViewController as! UINavigationController;
rootViewController.pushViewController(viewController, animated: true);
}
I get an error on "let rootViewController:.... = 2019-11-27 13:03:49.364864+0100 Geo[25133:2193886] Fatal error: Unexpectedly found nil while unwrapping an Optional value: file
Since SWIFT is new to me, I am not able to debug this message. How do I perform the redirection?

Answer 1

you need to use the below code :
let storyboard = UIStoryboard(name: "Main", bundle: nil);
let viewController: ViewController = storyboard.instantiateViewController(withIdentifier: "loginVC") as! ViewController;
let window = (UIApplication.shared.delegate as! AppDelegate).window!
DispatchQueue.main.async {
window.rootViewController = viewController
}

Answer 2

You need to assign the value for your rootViewController. Try this:
func userErrorLogout() {
print("user error logout")
let storyboard = UIStoryboard(name: "Main", bundle: nil);
let viewController: ViewController = storyboard.instantiateViewController(withIdentifier: "loginVC") as! ViewController;
let nav = UINavigationController(rootViewController: viewController)
self.window?.rootViewController = nav
}

Answer 3

You need to set the viewcontroller to window. You can do like below. This code also has transition animation it gives fade to transition.
// MARK: WINDOW SET
func gotoIntro() {
UIView.transition(with: window!, duration: 0.5, options: .transitionCrossDissolve, animations: {
UIView.performWithoutAnimation({
let introStoryboard = UIStoryboard(name: "Intro", bundle: nil)
let navigationController = introStoryboard.instantiateInitialViewController() as! UINavigationController
self.window?.rootViewController = navigationController
})
}, completion: nil)
}

Answer 4

As of iOS 13, pushing a VC at the start of a launch is not possible from AppDelegate anymore (Not 100% sure).
You must use SceneDelegate if you wish to present the view from your root.
To do so, simply do this inside your SceneDelegate file. I have tested this approach on my own app and is working 100%
func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
guard let windowScene = (scene as? UIWindowScene) else { return }
self.window = UIWindow(windowScene: windowScene)
// check if the token is valid
if valid {
let vc = UIStoryboard.init(name: "Main", bundle: Bundle.main).instantiateViewController(withIdentifier: "yourVC")
self.window?.rootViewController = vc
self.window?.makeKeyAndVisible()
}
else {
// token is invalid
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let rootVC = storyboard.instantiateViewController(identifier: "invalidVC")
let rootNC = UINavigationController(rootViewController: rootVC)
self.window?.rootViewController = rootNC
self.window?.makeKeyAndVisible()
}
}