App crashing when using Firebase Auth, reason: 'Default app has already been configured.'

I had a problem with a Messages Extension :

If you're in an App Extension, you have no delegate, and you'll have to put the FIRApp.configure() in the init of your main ViewController (or in the viewDidLoad as suggested).

Problem is : in a Messages Extension, if the user presses several messages in the thread opening your extension, init (or viewdidLoad) will be called several times, therefore crashing due to FIRApp.configure() called several times...

The solution I found was to create a static bool in the main View Controller :

    static var isAlreadyLaunchedOnce = false // Used to avoid 2 FIRApp configure

and I test it before calling FIRApp.configure() in the init or viewDidLoad :

// Configure Firebase
    // ------------------
    // We check if FIRApp has already been configured with a static var, else it will crash...
    if !MessagesViewController.isAlreadyLaunchedOnce {
        FIRApp.configure()

        MessagesViewController.isAlreadyLaunchedOnce = true
    }

This way, no more crashes.

Oh, I found a much more elegant way to solve the problem here : iOS Extension - Fatal Exception: com.firebase.core Default app has already been configured

    // Configure Firebase
    // ------------------
    if FIRApp.defaultApp() == nil {
        FIRApp.configure()            
    }

No more static this way ;)

I wrote FIRApp.configure() twice, that seemed to fix the error.

This is other solution about this issue. 1/ Check in the "AppDelegate.swift" we will see as below

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    // Override point for customization after application launch.
    FirebaseApp.configure()
    return true
}

2/ Remove "FirebaseApp.configure()" from above code to

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    // Override point for customization after application launch.

    return true
}

3/ Add below code into "AppDelegate.swift"

override init() {
    FirebaseApp.configure()
}

4/ Go to "ViewController.swift" and add the code

    if FirebaseApp.app() == nil {
        FirebaseApp.configure()
    }

5/ Build again and Run it's will work. Thanks!

For Swift 4,

if FirebaseApp.app() == nil {
/// code snippet
}

Class Name: AppDelegate+FCMPlugin.m

[FIRApp.configure()];

Put this at the top most of this method

- (BOOL)application:(UIApplication *)application customDidFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
 if(![FIRApp defaultApp]){
    [FIRApp configure];}}

You can call once in AppDelegate init method to configure.

override init() {
   // Firebase Init
   FIRApp.configure()
}

If you're using Scene delegate from and you have different iOS versions like 9, 10 up to 13, you must call in AppDelegate.swift in this way:

 if #available(iOS 13.0, *) {
 
 } else {
     FirebaseApp.configure()
 }

And in SceneDelegate.swift this way:

 if #available(iOS 13.0, *) {
   FirebaseApp.configure()
 }

These settings will exclude error like: *

*** Terminating app due to uncaught exception 'com.firebase.core', reason: 'Default app has already been configured.'

Seems like someone in the team had followed the firebase Ios setup steps and added the line Firebase.configure() in the AppDelegate.swift thinking it was needed for confirguration as it doesn't state that it's not needed for flutter in setup and only gives swift and objective-c as an option, which is understandable to confuse some people.

Solution was simple to remove that unnecessary line. , Thank you for the help.

Would recommend making it clearer for new developers in the firebase console setup.

just in case someone else stumble upon this problem. when use firebase sdk with googleSignIn sdk. you only have to configure them once. either do [[GGLContext sharedInstance] configureWithError: &configureError]; or [FIRApp configure]

Here is my code for AppDelegate.swift

import UIKit
import Flutter
import Firebase

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    GeneratedPluginRegistrant.register(with: self)
  FirebaseApp.configure()
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}

You can remove this this FirebaseApp.configure() or add

 if #available(iOS 13.0, *) {
 
 } else {
     FirebaseApp.configure()
 }

both are working for me

It's because you have already initialized FirebaseApp.configure() in the AppDelegate. Please make sure it's only configured once and the error should go.

I had same problem but got it working...

// Step #1 Here is my AppDelegeate I think it may be redundant but I got it working and had the same error.

class AppDelegate: NSObject, UIApplicationDelegate {
    override init() {
       // Firebase Init
       FirebaseApp.configure()
    }
  func application(_ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions:
        [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    FirebaseApp.configure()
    return true
  }
}

Step #2 for my function in my swiftui file where I create user account I add the 'if' statement before the Auth.auth() like such:

private func createNewCount(){
    if FirebaseApp.app() == nil {
           FirebaseApp.configure()
       }
    Auth.auth().createUser(withEmail: email, password: password) { result, err in
        if let err = err {
            print("Failed to create user", err)
            return
        }
        print("succesfully created user \(result?.user.uid ?? "")")
    }
    
}

For Swift 4

Had the same problem with crashing. When trying to reference from Firebase with a .plist file.

(This fixed my problem.)

Try writing this outside of or within the viewDidLoad method:

1. var ref: DatabaseReference!

Then reference it within the viewDidLoad method:

2. Database.database().reference()

And now it's:

FirebaseApp.configure()

Instead.