持久化用户Auth Flutter Firebase

Question

I am using Firebase Auth with google sign in Flutter. I am able to sign in however when I close the app(kill it), I have to sign up all over again. So is there a way to persist user authentication till specifically logged out by the user? Here is my auth class

import 'package:firebase_auth/firebase_auth.dart';
import 'package:google_sign_in/google_sign_in.dart';

class Auth {
  FirebaseAuth _firebaseAuth;
  FirebaseUser _user;

  Auth() {
    this._firebaseAuth = FirebaseAuth.instance;
  }

  Future<bool> isLoggedIn() async {
    this._user = await _firebaseAuth.currentUser();
    if (this._user == null) {
      return false;
    }
    return true;
  }

  Future<bool> authenticateWithGoogle() async {
    final googleSignIn = GoogleSignIn();
    final GoogleSignInAccount googleUser = await googleSignIn.signIn();
    final GoogleSignInAuthentication googleAuth =
    await googleUser.authentication;
    this._user = await _firebaseAuth.signInWithGoogle(
      accessToken: googleAuth.accessToken,
      idToken: googleAuth.idToken,
    );
    if (this._user == null) {
      return false;
    }
    return true;
    // do something with signed-in user
  }
}

Here is my start page where the auth check is called.

import 'package:flutter/material.dart';
import 'auth.dart';
import 'login_screen.dart';
import 'chat_screen.dart';

class Splash extends StatefulWidget {

  @override
  _Splash createState() => _Splash();
}

class _Splash extends State<Splash> {

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: CircularProgressIndicator(
          value: null,
        ),
      ),
    );
  }

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

  Future<void> _handleStartScreen() async {
    Auth _auth = Auth();
    if (await _auth.isLoggedIn()) {
      Navigator.of(context).pushReplacementNamed("/chat");
    }
    Navigator.pushReplacement(context, MaterialPageRoute(builder: (BuildContext context) => LoginScreen(auth: _auth,)));
  }
}

Answer 1

I believe your problem is routing. In my apps I use FirebaseAuth and it works just as you say you wanted to, and I don't persist any login token. However, I don't know why your approach of using a getUser is not working.

Try to adjust your code to use onAuthStateChanged . EDIT: As of 2022, with Flutter 3, I noticed it worked better with userChanges instead.

Basically, on your MaterialApp , create a StreamBuilder listening to _auth.userChanges() and choose your page depending on the Auth status.

I'll copy and paste parts of my app so you can have an idea:

[...]

final FirebaseAuth _auth = FirebaseAuth.instance;

Future<void> main() async {
  FirebaseApp.configure(
    name: '...',
    options:
      Platform.isIOS
        ? const FirebaseOptions(...)
        : const FirebaseOptions(...),
    );
  
  [...]  

  runApp(new MaterialApp(
    title: '...',
    home: await getLandingPage(),
    theme: ThemeData(...),
  ));
}

Future<Widget> getLandingPage() async {
  return StreamBuilder<FirebaseUser>(
    stream: _auth.userChanges(),
    builder: (BuildContext context, snapshot) {
      if (snapshot.hasData && (!snapshot.data!.isAnonymous)) {
        return HomePage();
      }
      
      return AccountLoginPage();
    },
  );
}

Answer 2

Sorry, it was my mistake. Forgot to put the push login screen in else.

  Future<void> _handleStartScreen() async {
    Auth _auth = Auth();
    if (await _auth.isLoggedIn()) {
      Navigator.of(context).pushReplacementNamed("/chat");
    }
    else {
        Navigator.pushReplacement(context, MaterialPageRoute(builder: (BuildContext context) => LoginScreen(auth: _auth,)));
    }
  }

Answer 3

void main() {
FirebaseAuth.instance.authStateChanges().listen((User user) {
  if (user == null) {
          runApp(MyApp(auth : false);
        } else {
          runApp(MyApp(auth : false);
       }
    });
}

class MyApp extends StatefulWidget {
  final bool auth;
  MyApp({this.auth});
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  return MaterialApp(
  ......
  ......
  home: widget.auth ? MainScreen() : AuthScreen();
);

Answer 4

You can use shared_preferences to keep alive your session even when you kill the app. Here is the documentation https://pub.dartlang.org/packages/shared_preferences .

Also I've heard that it's possible to use sqlite to persist the session.

Answer 5

Add this code. It should work fine.

FirebaseAuth auth = FirebaseAuth.instance;

auth.setPersistence(Persistence.SESSION);

Answer 6

You can use my code, You can use userChanges() instead of authStateChanges()

Notifies about changes to any user updates.

This is a superset of both [authStateChanges] and [idTokenChanges]. It provides events on all user changes, such as when credentials are linked, unlinked and when updates to the user profile are made. The purpose of this Stream is for listening to realtime updates to the user state (signed-in, signed-out, different user & token refresh) without manually having to call [reload] and then rehydrating changes to your application.

final Stream<User?> firebaseUserChanges = firebaseAuth.userChanges();

Answer 7

One more simple example:

Future<bool> isUserLoggedIn() async {
   final User? user = FirebaseAuth.instance.currentUser;
   return user != null;
}


class InitialScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: FutureBuilder<bool>(
        future: isUserLoggedIn(),
        builder: (_, snapshot) {
          if (snapshot.hasData) {
            if (snapshot.data ?? false) {
              Navigator.of(context).push(MaterialPageRoute(builder: (context) => UnauthScreen()));
            } else {
              Navigator.of(context).push(MaterialPageRoute(builder: (context) => HomeScreen()));
            }
          }
         return const Center(child: CircularProgressIndicator());
       },
      ),
    );
   }
 }

Answer 8

I was able to achieve it by checking the firebase instance currentUser value. if null I routed to my Signup page. If not, then I routed to my HomePage. Not sure if there is anything wrong with this implementation (its working well so far) but seems simpler than the StreamBuilder solution posted above.

  home: getLandingPage(),
        routes: {
          (...)
 }

    Widget getLandingPage() {
  if (_auth.currentUser == null) {
    return SignupPage();
  } else {
    return HomePage();
  }
}