Null error when I want my firebase user id with currentUser()

Question

Error

NoSuchMethodError: The method 'currentUser' was called on null.

Receiver: null

Tried calling: currentUser()

I'm interesting in know where i need to using this code:

String _uid = '';
      void initState() {
        super.initState();
        auth.currentUser().then((userId) {
          setState(() {
            _uid = userId;
          });
        });
      }

This code is from the home_page.dart (see below)

I had also tried to using:

widget.auth.current....

root_page

In bottom of the file i had tried different approach. Instead of HomePage then _HomePageState(comments out)

class RootPage extends StatefulWidget {

  RootPage({this.auth});
  final BaseAuth auth;

  @override
  State<StatefulWidget> createState() => new _RootPageState();

}

enum AuthStatus {
  notSignedIn,
  signedIn
}

class _RootPageState extends State<RootPage>{

  AuthStatus authStatus = AuthStatus.notSignedIn;

  @override
  void initState() {
    super.initState();
    widget.auth.currentUser().then((userId) {
      setState(() {
        authStatus = userId == null ? AuthStatus.notSignedIn : AuthStatus.signedIn;
      });
    });
  }

  void _signedIn(){
    setState(() {
      authStatus = AuthStatus.signedIn;
    });
  }

  void _signedOut() {
    setState(() {
      authStatus = AuthStatus.notSignedIn;
    });
  }

  @override
  Widget build(BuildContext context) {
    switch(authStatus) {
      case AuthStatus.notSignedIn:
        return new LoginPage(
          auth: widget.auth,
          onSignedIn: _signedIn,
        );
      case AuthStatus.signedIn:
        /*
        return new HomePageState(
          auth: widget.auth,
          onSignedOut: _signedOut,
        );
        */
        return new HomePage(
          auth: widget.auth,
          onSignedOut: _signedOut,
        );
    }
  }
}

auth.dart

This is the class I'm using to get current user from auth.

abstract class BaseAuth{
  Future<String> signInWithEmailAndPassword(String email, String password);
  Future<String> createUserWithEmailAndPassword(String email, String password);
  Future<String> currentUser();
  Future<void> signOut();
}

class Auth implements BaseAuth{

  final FirebaseAuth _firebaseAuth = FirebaseAuth.instance;

  Future<String> signInWithEmailAndPassword(String email, String password) async {
    FirebaseUser user = await _firebaseAuth.signInWithEmailAndPassword(email: email, password: password);
    return user.uid;
  }

  Future<String> createUserWithEmailAndPassword(String email, String password) async {
    FirebaseUser user = await _firebaseAuth.createUserWithEmailAndPassword(email: email, password: password);
    return user.uid;
  }

  Future<String> currentUser() async {
    FirebaseUser user = await _firebaseAuth.currentUser();
    return user.uid;
  }

  Future<void> signOut() async {
    return _firebaseAuth.signOut();
  }

}

home_page.dart

I had tried different things in this file but get different errors.

class HomePage extends StatefulWidget {

  HomePage({this.auth, this.onSignedOut});

  final BaseAuth auth;
  final VoidCallback onSignedOut;

  void _signOut() async {
    try {
      await auth.signOut();
      onSignedOut();
    } catch (e) {
      print(e);
    }
  }
  @override
  State<StatefulWidget> createState() => new _HomePageState();
}

class _HomePageState extends State<HomePage> {
/*
  _HomePageState({this.auth, this.onSignedOut});
  final BaseAuth auth;
  final VoidCallback onSignedOut;
  */
  //final BaseAuth auth;

  String _uid = '';

  @override
  void initState() {
    super.initState();
    auth.currentUser().then((userId) {
      setState(() {
        _uid = userId;
      });
    });
  }

Answer 1

_auth.currentUser() does not return the user ID, it returns a FirebaseUser object.

Change it like this :

auth.currentUser().then((user) {
  if (user == null || user.isAnonymous) {
    // what will you do?
    return;
  }
  setState(() {
    _uid = user.uid;
  });
});

Yet, I would recommend to monitor the onAuthStateChanged stream instead. This way you will be informed when the user logs in or logs out immediately.

Check this article, it covers it in depth.

Answer 2

You can use like this.

someMethod() async {
   FirebaseUser user = await FirebaseAuth.instance.currentUser();
   print(user.uid);
}