在 flutter 中的 null 上调用了 getter 'uid'

Question

I'm implementing firebase authentication in flutter application but while trying to get user uid, it is crashing and show noSuchMethodError uid is null, if anyone could help, it is deeply appreciated

• That's how i init my variables

class _UserRegistrationState extends State<UserRegistration> {

FirebaseAuth auth;
DocumentReference reference;
Reference storage;

PickedFile imageUri;
final ImagePicker _imagePicker = new ImagePicker();

@override
void initState() {
  super.initState();

  auth =   FirebaseAuth.instance;
   
  // the uid is where the logcat is pointing too and it is null
  reference =  FirebaseFirestore.instance.collection('users').doc(auth.currentUser.uid);
  storage =  firebase_storage.FirebaseStorage.instance.ref('avatar').child(auth.currentUser.uid);
}

Answer 1

currentUser → User? Returns the current User if they are currently signed-in, or null if not.

So most likely thing is that you are not logged in and therefore passing null to reference

Answer 2

When you sign in to Firebase Authentication, the SDK automatically persists the user's credentials in local storage. When you restart the app, the SDK tries to restore the user's authentication state from the stored credentials. This requires that it calls the servers to get a new ID token, and for example to check if the account was deleted/disabled in the meantime.

Depending on the platform where you run your code, the calls to the server may have completed before your auth.currentUser runs, or not. To safely respond to the user state, always use an auth state listener as shown in the FlutterFire documentation on responding to auth state changes :

@override
void initState() {
  super.initState();

  auth = FirebaseAuth.instance;
   
  FirebaseAuth.instance.authStateChanges().listen((User user) {
    if (user == null) {
      print('User is currently signed out!');
    } else {
      print('User is signed in!');
      reference =  FirebaseFirestore.instance.collection('users').doc(auth.currentUser.uid);
      storage =  firebase_storage.FirebaseStorage.instance.ref('avatar').child(auth.currentUser.uid);
    }
  });
}