authStateChanges
- Flutter course
- Advanced
- Lesson 19/69
- 4 min
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
}
});Practice 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.
Starter code
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 {
// durum akışını dinle
// kullanıcı null ise 'yok' yazdır
// 10ms bekle
}Sample 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));
}Expected output
yok
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does authStateChanges return?
- Future<User?>
- User?
- Stream<User?> Correct answer
- Widget
Explanation: authStateChanges returns a Stream<User?>; a new value is emitted whenever the auth state changes.
2 Listen to the state stream
auth.____().listen((user) {
print(user?.email);
});auth.authStateChanges().listen((user) {
print(user?.email);
});Explanation: authStateChanges returns the stream that fires when the auth state changes; it is listened to with listen.
3 authStateChanges parts
| Term | Meaning |
|---|---|
authStateChanges |
State change stream |
Stream<User?> |
Return type |
listen |
Listens to the stream |
User? |
null when no session |