I have the following code and I need to keep users logged when they reopen the app. I have a flutter phone authentication service from firebase. The given is function to verify google phone authentication. There is a button when pressed 2 functions mentioned below to get call named verifyPhoneNumber() & signInWithPhoneNumber().

void verifyPhoneNumber() async {
if (_formKey.currentState!.validate()) {
  setState(() {
    loading = true;
  });
  PhoneVerificationCompleted verificationCompleted =
      (PhoneAuthCredential phoneAuthCredential) async {
    User? user;
    bool error = false;
    try {
      user = (await firebaseAuth.signInWithCredential(phoneAuthCredential))
          .user!;
    } catch (e) {
      print("Failed to sign in: "   e.toString());
      error = true;
    }
    if (!error && user != null) {
      String id = user.uid;
      //here you can store user data in backend
      Navigator.pushReplacement(
          context,
          MaterialPageRoute(
              builder: (context) => PhoneAuthDataNext(
                    phone: phoneNumber,
                  )));
    }
  };

  PhoneVerificationFailed verificationFailed =
      (FirebaseAuthException authException) {
    showToast(authException.message!);
  };
  PhoneCodeSent codeSent =
      (String? verificationId, [int? forceResendingToken]) async {
    showToast('Please check your phone for the verification code.');
    this.forceResendingToken = forceResendingToken;
    _verificationId = verificationId;
  };
  PhoneCodeAutoRetrievalTimeout codeAutoRetrievalTimeout =
      (String verificationId) {
    _verificationId = verificationId;
  };
  try {
    await firebaseAuth.verifyPhoneNumber(
        phoneNumber: phoneNumber!,
        timeout: const Duration(seconds: 10),
        forceResendingToken:
            forceResendingToken != null ? forceResendingToken : null,
        verificationCompleted: verificationCompleted,
        verificationFailed: verificationFailed,
        codeSent: codeSent,
        codeAutoRetrievalTimeout: codeAutoRetrievalTimeout);
    showOtpScreen = true;
  } catch (e) {
    showToast("Failed to Verify Phone Number: $e");
    showOtpScreen = false;
  }
  setState(() {
    loading = false;
  });
}

}

void signInWithPhoneNumber() async {
    bool error = false;
    User? user;
    AuthCredential credential;
    setState(() {
      loading = true;
    });
    try {
      credential = PhoneAuthProvider.credential(
        verificationId: _verificationId!,
        smsCode: otpEditingController.text,
      );
      user = (await firebaseAuth.signInWithCredential(credential)).user!;
    } catch (e) {
      showToast("Failed to sign in: "   e.toString());
      error = true;
    }
    if (!error && user != null) {
      credential = PhoneAuthProvider.credential(
        verificationId: _verificationId!,
        smsCode: otpEditingController.text,
      );
      UserCredential userCredential =
          await firebaseAuth.signInWithCredential(credential);
      storeTokenAndData(userCredential);

      //here you can store user data in backend
      Navigator.pushReplacement(
          context,
          MaterialPageRoute(
              builder: (context) => PhoneAuthDataNext(
                    phone: phoneNumber,
                    credential: credential,
                  )));
    }
    setState(() {
      loading = false;
    });
  }

Please Give me a solution.

CodePudding user response：

Firebase already restores the user credentials from local storage/shared preferences when the app restarts. But this is an asynchronous process, since it requires a call to the server.

To detect and respond to the authentication state, listen to the authStateChanges stream as shown in the documentation on authentication state.

FirebaseAuth.instance
  .authStateChanges()
  .listen((User? user) {
    if (user == null) {
      print('User is currently signed out!');
    } else {
      print('User is signed in!');
    }
  });

You'll typically want to wrap FirebaseAuth.instance.authStateChanges() in a StreamBuilder to show the correct UI state based on whether the user is signed in.

CodePudding user response：

Firebase already handles the 'session' for you. You can use the authStateChanges method to check auth state and update your UI as I have done with the code below

class AuthGate extends StatelessWidget {
  const AuthGate({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return StreamBuilder(
      stream: FirebaseAuth.instance.authStateChanges(),
      builder: (BuildContext context, AsyncSnapshot<User?> snapshot) {
        if (snapshot.hasData) {
          return HomePage();
        }
        return LoginPage();
      },
    );
  }
}