iOS Swift中注销后如何调用AppDelegate并重新注册FCM Token？

Hey there, let's tackle your FCM token issue and the AppDelegate question one by one—this is a common gotcha with Firebase Cloud Messaging on iOS, so I’ve got you covered!

Fixing the FCM Token Re-registration Issue After Logout #

First, let’s break down why you can’t re-register the FCM token after logout:

• You’re only deleting the token from your backend, but Firebase still holds the old token locally. Without telling Firebase to invalidate it, it won’t generate a new token automatically.
• Your current setup relies solely on a notification to receive the token, but if the token isn’t refreshed (because Firebase thinks it’s still valid), that notification never fires.
• You’re adding the same notification observer twice (in viewDidLoad and viewDidAppear), which can lead to duplicate calls and unexpected behavior.

Here’s how to fix it:

1. Properly Invalidate the FCM Token During Logout #

When the user logs out, don’t just call your backend API—also tell Firebase to delete the local token. Add this to your logout flow:

import FirebaseMessaging

func handleLogout() {
    // 1. Call your backend API to delete the token
    // ... your existing backend call here ...
    
    // 2. Invalidate Firebase's local token
    Messaging.messaging().deleteToken { error in
        if let error = error {
            print("Failed to delete FCM token: \(error.localizedDescription)")
        } else {
            print("FCM token deleted successfully")
        }
    }
    
    // 3. Navigate to login screen
    // ... your navigation code here ...
}

2. Optimize Token Fetching in LoginViewController #

Instead of waiting passively for a notification, actively request the token when the login screen loads. Also, fix the duplicate observer issue:

var fcmval: String?
let baseURL = "https://url"

override func viewDidLoad() {
    super.viewDidLoad()
    // Add observer ONCE to catch token updates
    NotificationCenter.default.addObserver(
        self,
        selector: #selector(fcmTokenUpdated(notification:)),
        name: Notification.Name("FCMToken"),
        object: nil
    )
}

deinit {
    NotificationCenter.default.removeObserver(self)
}

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    // Actively fetch the FCM token when the login screen appears
    fetchFCMToken()
}

@objc func fcmTokenUpdated(notification: Notification) {
    if let userInfo = notification.userInfo as? [String: String],
       let token = userInfo["token"] {
        updateFCMToken(token: token)
    }
}

private func fetchFCMToken() {
    Messaging.messaging().token { [weak self] token, error in
        guard let self = self else { return }
        if let error = error {
            print("Error fetching FCM token: \(error.localizedDescription)")
            return
        }
        if let token = token {
            self.updateFCMToken(token: token)
        }
    }
}

private func updateFCMToken(token: String) {
    self.fcmval = token
    print("FCM token received: \(token)")
    // Update your login view with the token
    A8FlowBuilder(self).showLoginView(url: baseURL, fcm: token)
}

3. Handle Asynchronous Token Fetching #

Since fetching the token is async, make sure your login flow doesn’t proceed until the token is available. If your login button triggers the API call directly, add a check:

@IBAction func loginButtonTapped(_ sender: UIButton) {
    guard let token = fcmval else {
        // Show a loading state and fetch the token first
        fetchFCMToken()
        return
    }
    // Proceed with login API call using the token
}

Calling AppDelegate Methods After Logout #

There are two clean ways to trigger code in AppDelegate.swift after logout:

Option 1: Directly Reference AppDelegate #

If you need to call a specific method, you can access the AppDelegate instance directly:

// In your logout handler
if let appDelegate = UIApplication.shared.delegate as? AppDelegate {
    appDelegate.handlePostLogoutCleanup()
}

Then add the method to AppDelegate.swift:

@objc func handlePostLogoutCleanup() {
    // Perform cleanup tasks (e.g., reset app state, clear cached data)
    do {
        try Messaging.messaging().deleteToken()
    } catch {
        print("Error deleting token in AppDelegate: \(error)")
    }
}

Option 2: Use NotificationCenter (More Decoupled) #

For better separation of concerns, send a notification when the user logs out, and have AppDelegate listen for it:

1. In AppDelegate.swift, add the observer in didFinishLaunchingWithOptions:

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    // ... other setup code ...
    NotificationCenter.default.addObserver(
        self,
        selector: #selector(handleLogoutNotification),
        name: Notification.Name("UserDidLogout"),
        object: nil
    )
    return true
}

@objc private func handleLogoutNotification() {
    handlePostLogoutCleanup()
}

2. In your logout handler, post the notification:

func handleLogout() {
    // ... your logout logic ...
    NotificationCenter.default.post(name: Notification.Name("UserDidLogout"), object: nil)
}

内容的提问来源于stack exchange，提问作者PvUIDev