How to Maintain User Login State Across App Restarts Using Firebase Authentication?

One-Time Login in App Using FirebaseAuth

Problem:

How can I ensure that users remain logged in after closing and restarting an app using Firebase authentication and without implementing a logout feature?

Solution:

The solution involves leveraging a listener to monitor the user's authentication state. This listener will automatically redirect users to the appropriate activity based on whether they are logged in or not.

Implementation:

1. Create the FirebaseAuth Object:

FirebaseAuth firebaseAuth = FirebaseAuth.getInstance();

2. Implement the AuthStateListener:

FirebaseAuth.AuthStateListener authStateListener = new FirebaseAuth.AuthStateListener() {
    @Override
    public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
        FirebaseUser firebaseUser = firebaseAuth.getCurrentUser();
        if (firebaseUser != null) {
            // User is logged in
            Intent intent = new Intent(LoginActivity.this, MainActivity.class);
            startActivity(intent);
            finish();
        } else {
            // User is not logged in
            Intent intent = new Intent(MainActivity.this, LoginActivity.class);
            startActivity(intent);
        }
    }
};

3. Start Listening for Changes:

@Override
protected void onStart() {
    super.onStart();
    firebaseAuth.addAuthStateListener(authStateListener);
}

@Override
protected void onStop() {
    super.onStop();
    firebaseAuth.removeAuthStateListener(authStateListener);
}

4. Place Listeners in LoginActivity and MainActivity:

Repeat steps 2 and 3 in both the LoginActivity and MainActivity to ensure proper handling of logged-in and logged-out states.

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