Black screen flashes between Launch and first ViewController in SceneDelegate - swift

Question

I am using SceneDelegate.swift to decide which ViewController is shown with this code:
guard let windowScene = (scene as? UIWindowScene) else { return }
if Auth.auth().currentUser != nil {
AuthenticationService.automaticSignIn(onSuccess: {
let window = UIWindow(windowScene: windowScene)
self.window = window
let mainstoryboard:UIStoryboard = UIStoryboard(name: "Login", bundle: nil)
let newViewcontroller:UIViewController = mainstoryboard.instantiateViewController(withIdentifier: "TabBarControllerID") as! TabBarController
window.rootViewController = newViewcontroller
window.makeKeyAndVisible()
}, onError: {
let window = UIWindow(windowScene: windowScene)
self.window = window
let mainstoryboard:UIStoryboard = UIStoryboard(name: "Login", bundle: nil)
let newViewcontroller:UIViewController = mainstoryboard.instantiateViewController(withIdentifier: "LoginViewControllerID") as! LoginViewController
window.rootViewController = newViewcontroller
window.makeKeyAndVisible()
})
} else {
let window = UIWindow(windowScene: windowScene)
self.window = window
let mainstoryboard:UIStoryboard = UIStoryboard(name: "Login", bundle: nil)
let newViewcontroller:UIViewController = mainstoryboard.instantiateViewController(withIdentifier: "LoginViewControllerID") as! LoginViewController
window.rootViewController = newViewcontroller
window.makeKeyAndVisible()
}
}
Between the transition, a black screen appears (in my .gif for about 0.2 seconds), depending on the loading time. Sorry for the bad quality and the short duration, but you will see it:
Where does this black screen come from?

Answer 1

try to change this line:-
self.window!.rootViewController = UINavigationController(rootViewController: DashboardVC)
self.window!.makeKeyAndVisible()

Answer 2

The issue seems to be caused by a 'gap' in the presentation between the launch-storyboard and the window that is made visible. The appleIDProvider is async.
A workaround, rather than a fix, is to present a temporary View (with the same color or content as your launch-storyboard) and replace it once authorization is done;
func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
guard let windowScene = scene as? UIWindowScene else { return }
let window = UIWindow(windowScene: windowScene)
window.rootViewController = UIHostingController(rootView: TempView())
self.window = window
window.makeKeyAndVisible()
let user = User.shared
let appleIDProvider = ASAuthorizationAppleIDProvider()
appleIDProvider.getCredentialState(forUserID: user.id) { (credentialState, error) in
switch credentialState {
case .authorized:
DispatchQueue.main.async {
user.authenticated = true
window.rootViewController = UIHostingController(rootView: HomeView(showAlert: false, showSendview: false, showAccountview: false))
}
default:
DispatchQueue.main.async {
user.authenticated = false
window.rootViewController = UIHostingController(rootView: SignInView().environment(\.window, window))
}
}
}
}