authStateChanges

Listen to session changes with authStateChanges.

What is authStateChanges?

The authStateChanges method returns a Stream<User?> that fires events whenever the auth state changes. When the user signs in, a User is emitted; on sign-out, null is emitted. It also emits the current state once on startup, making it ideal for session monitoring.

auth.authStateChanges().listen((user) {
  print(user?.email ?? 'misafir');
});

Listening to the stream

When you listen to the stream with listen, the callback is called on every auth change. Inside this callback you perform side effects such as navigation, snackbars, or widget updates. It can also be used with StreamBuilder for automatic rebuilds.

auth.authStateChanges().listen((user) {
  if (user == null) {
    // giriş ekranına git
  } else {
    // ana ekrana git
  }
});

Exercise Listen to the state stream

Get the auth instance, listen to the authStateChanges stream with listen. Print 'yok' if user is null. Wait 10 milliseconds after starting to listen.

Show example solution

class User {
  final String email;
  User(this.email);
}

class FirebaseAuth {
  static final FirebaseAuth instance = FirebaseAuth._();
  FirebaseAuth._();
  User? _user;

  Stream<User?> authStateChanges() async* {
    yield _user;
  }
}

void main() async {
  final auth = FirebaseAuth.instance;
  auth.authStateChanges().listen((user) {
    print(user?.email ?? 'yok');
  });
  await Future.delayed(Duration(milliseconds: 10));
}

Test yourself

What does authStateChanges return?
- Future<User?>
- User?
- Stream<User?>
- Widget
Show answer

Stream<User?> — authStateChanges returns a Stream<User?>; a new value is emitted whenever the auth state changes.

Listen to the state stream

auth.____().listen((user) {
  print(user?.email);
});

Show answer

auth.authStateChanges().listen((user) {
  print(user?.email);
});

authStateChanges parts

authStateChanges

State change stream
Stream<User?>

Return type
listen

Listens to the stream
User?

null when no session

Next lesson: Summary - Firebase Auth

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