NSInternalInconsistencyException: Firebase crashes SwiftUI app on launch - ios

Question

I am trying to add Firebase auth via Apple Sign-in and have got this error:
crashed due to an uncaught exception `NSInternalInconsistencyException`. Reason: The default FirebaseApp instance must be configured before the default Authinstance can be initialized. One way to ensure this is to call `FirebaseApp.configure()` in the App Delegate's `application(_:didFinishLaunchingWithOptions:)` (or the `#main` struct's initializer in SwiftUI)
This is how I launch Firebase:
import Firebase
import SwiftUI
class AppDelegate: NSObject, UIApplicationDelegate {
func application(
_ application: UIApplication,
didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]? = nil
) -> Bool {
FirebaseApp.configure()
return true
}
}
I did not install the Firebase package directly, but instead added this package. which I believe added Firebase as one of its dependency. I have checked other solutions but they all rely on CocoaPods while I'm using the Swift Package Manager. Not sure how I can resolve this error.
App calling AppDelegate:
import FirebaseService
import SwiftUI
#main
struct SomeApp: App {
#UIApplicationDelegateAdaptor(AppDelegate.self) var appDelegate
#State private var authState = AuthState()
var body: some Scene {
WindowGroup {
switch authState.value {
case .undefined:
ProgressView()
case .authenticated:
ContentView()
case .notAuthenticated:
AuthView()
}
}
}
}

Answer 1

This error message indicates that another part of your app tries to access Firebase Auth before Firebase is initialised in your your app delegate.
Looking at the code of Rebeloper's package which you're using, we can see that it calls Auth.auth().addStateDidChangeListener in line 16 of AuthListener. Since you create an instance of AuthState (another class from Rebeloper's library), this is executed before Firebase is initialised.
Instead of using an undocumented third party library, I would recommend implementing this yourself - especially since it's only a few lines of code.
To see how this is done, check out Getting started with Firebase Auth for Apple platforms - Firebase Fundamentals, which not only explains Firebase Auth and how to handle authentication state in detail, but also includes the corresponding source code.
As an added bonus, this contains a beautiful signup/login form:
For reference, here is the source code for registering an authentication state listener in an ObserableObject:
#MainActor
class AuthenticationViewModel: ObservableObject {
#Published var email = ""
#Published var password = ""
#Published var confirmPassword = ""
#Published var flow: AuthenticationFlow = .login
#Published var isValid = false
#Published var authenticationState: AuthenticationState = .unauthenticated
#Published var errorMessage = ""
#Published var user: User?
#Published var displayName = ""
init() {
registerAuthStateHandler()
// ...
}
private var authStateHandler: AuthStateDidChangeListenerHandle?
func registerAuthStateHandler() {
if authStateHandler == nil {
authStateHandler = Auth.auth().addStateDidChangeListener { auth, user in
self.user = user
self.authenticationState = user == nil ? .unauthenticated : .authenticated
self.displayName = user?.email ?? ""
}
}
}
// ...
}