Check if user is logged in or not before authentication using google sign in - flutter

Issue

In my flutter app, am trying to check if a user is logged in or not before authenticating the user in firebase, so if he is not then do not authenticate

 Future<String> loginUserWithGoogle() async {
    String returnValue = "error";
    GoogleSignIn _googleSignIn = GoogleSignIn(
      scopes: [
        'email',
        'https://www.googleapis.com/auth/contacts.readonly',
      ],
    );
    UserData _user = UserData();
    try {
      GoogleSignInAccount _googleUser = await _googleSignIn.signIn();
      GoogleSignInAuthentication _googleAuth = await _googleUser.authentication;
      final AuthCredential credential = GoogleAuthProvider.credential(idToken: _googleAuth.idToken, accessToken: _googleAuth.accessToken);
      UserCredential _authResult = await _auth.signInWithCredential(credential);
      if (_authResult.additionalUserInfo.isNewUser) {
        String userGoogleName = _authResult.user.displayName;
        List userSplitName = userGoogleName.split(" ");
        String userGoogleFirstName = userSplitName.first;
        String userGoogleLastName = userSplitName.last;

        SharedPreferences prefs = await SharedPreferences.getInstance();
        await prefs.setString('googleUid', _authResult.user.uid);
        await prefs.setString('googleEmail', _authResult.user.email);
        await prefs.setString('googleFirstName', userGoogleFirstName);
        await prefs.setString('googleLastName', userGoogleLastName);
        await prefs.setString('googleUserType', "user");

        returnValue = "new";
      } else {
        _currentUser = await RealDatabase().getUserData(_authResult.user.uid);
        if (_currentUser != null) {
          returnValue = "success";
        }
      }
    } on PlatformException catch (e) {
      returnValue = e.message;
    } catch (e) {
      print(e);
    }
    return returnValue;
  }
}

Here what I want to check is that if it is a new user then save his google data in sharedpreference and take him to another page where he can complete some other registration and then sign him in. but what this code does is that if it is a new user it will authenticate, save the info in sharedpeference and then take him to the page and if maybe that user decided to go back to the previous page (since i use Navigator.push(context)) and still click the google sign in button again then it will take him to the home screen without him completing the other registration I want him to do because it already authenticated him first. So please is there a way to do this without first authenticating the user.

Solution

You can use stream provider to control if user logged in or not. Here is an example how to use stream provider in your project; https://flutterbyexample.com/lesson/stream-provider.

Answered By - Timur Turbil