ViewController appears mulitple times when creating a navigationController programmatically in swift - ios

Question

I have been creating my app completely from scratch programmatically, without using Storyboards.
My app is integrated with Firebase, and uses Facebook login.
My setup is fairly simple:
Launch the app -> takes you to the first VC called WelcomeViewController.
There is a check that happens in the viewDidLoad method to see if a user is already signed in and exists. If there is, it sends you straight to the second VC called FilmsViewController
The FilmsViewController is a collectionViewController that displays films. The user can press a film, and it takes them to more information about that film.
(For reference, I am already signed in with Facebook in my app)
I have a current issue, where when step 2 above happens, it transitions to the FilmsViewController, but it does it like 2 or 3 times. So you see the new VC appear like 2 or 3 times, then the content loads. If you press the Back button in the nav bar, it takes you back through the 2 or 3 viewControllers that it loaded before taking you back to the WelcomeViewController.
I have set my views up as follows.
In AppDelegate.swift:
var window: UIWindow?
var navController: UINavigationController?
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
// Override point for customization after application launch.
navController = UINavigationController()
let firstViewController: WelcomeViewController = WelcomeViewController()
self.navController!.pushViewController(firstViewController, animated: true)
window = UIWindow(frame: UIScreen.main.bounds)
window?.rootViewController = navController
window?.makeKeyAndVisible()
return true
}
In the WelcomeViewController in the viewDidLoad:
FIRAuth.auth()?.addStateDidChangeListener { auth, user in
if let user = user {
// User is signed in.
// Direct the user to the home screen
let toFilmListVC = FilmsViewController(collectionViewLayout: UICollectionViewFlowLayout())
self.navigationController?.pushViewController(toFilmListVC, animated: true)
} else { ...
}
}
I have looked loads for a solution - and nothing. I've only found one post on this issue, where someone said the solution was to change the class name of that controller, which I have already done and it didn't change anything.
Can anyone help me resolve this, please? Thank you.

Answer 1

The addStateDidChangeListener is probably being called multiple times.
You should modify it to check whether a FilmsViewController has already been pushed, to prevent pushing another one:
FIRAuth.auth()?.addStateDidChangeListener { auth, user in
if let user = user {
// User is signed in.
// Direct the user to the home screen
// Only push one FilmsViewController onto the navigation stack!
var shouldPush = true
if let navigationController = self.navigationController {
for viewController in navigationController.viewControllers {
if viewController is FilmsViewController {
shouldPush = false
}
}
}
if shouldPush {
let toFilmListVC = FilmsViewController(collectionViewLayout: UICollectionViewFlowLayout())
self.navigationController?.pushViewController(toFilmListVC, animated: true)
}
} else { ...
}
}

Answer 2

I know the above solutions works, but to make it look extremely simple.
here is the code i wrote in my project.
let someController = SomeController.someController()
if !(self.navigationController!.viewControllers.contains(someController)){
self.navigationController?.pushViewController(someController, animated:true)
}
only push the controller to navigation bar if the controller is not exist.