如何在flutter中成功检测firebase用户注册和登录

Question

As per the documentation of FlutterFire, there are two different methods for signIn and signUp for email and password authentication.

For signUp

try {
  UserCredential userCredential = await FirebaseAuth.instance.createUserWithEmailAndPassword(
    email: "barry.allen@example.com",
    password: "SuperSecretPassword!"
  );
} on FirebaseAuthException catch (e) {
  if (e.code == 'weak-password') {
    print('The password provided is too weak.');
  } else if (e.code == 'email-already-in-use') {
    print('The account already exists for that email.');
  }
} catch (e) {
  print(e);
}

For signIn

try {
  UserCredential userCredential = await FirebaseAuth.instance.signInWithEmailAndPassword(
    email: "barry.allen@example.com",
    password: "SuperSecretPassword!"
  );
} on FirebaseAuthException catch (e) {
  if (e.code == 'user-not-found') {
    print('No user found for that email.');
  } else if (e.code == 'wrong-password') {
    print('Wrong password provided for that user.');
  }
}

By this code I can handle error by FirebaseAuthException and stop some loading progress. But how do I detect that user successfully register and do something as per success registration?

Answer 1

But how do I detect that user successfully register?

It is actually detailed in the documentation section that explains the code you mention in your question.

In particular, for registration the doc says:

The method is a two-step operation ; it will first create the new account (if it does not already exist and the password is valid) and then automatically sign in the user in to that account . If you are listening to changes in authentication state, a new event will be sent to your listeners .

To listen to changes in authentication state you can call the authStateChanges() method on your FirebaseAuth instance, as follows:

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

---

For signIn, it is the same. The doc states that:

Once successful, if you are listening to changes in authentication state, a new event will be sent to your listeners.

Refer to the registration case above.

---

So, in summary, on one hand you call the methods to either register ( createUserWithEmailAndPassword() ) or sign-in ( signInWithEmailAndPassword() ) and, on the other hand, you set a listener that listens to changes in authentication state. The listener alerts you when the call to one of the two methods is successful.

The on FirebaseAuthException catch (e) {...} blocks deals with the cases when the call to one of the two methods is not successful.

---

Finally, note the following article from the Firebase Developers Medium publication: it presents a slightly different approach, declaring async methods which check if the user object returned by the methods is null or not, and call setState() accordingly.

For example:

void _register() async {
  final FirebaseUser user = (await 
      _auth.createUserWithEmailAndPassword(
        email: _emailController.text,
        password: _passwordController.text,
      )
  ).user;
  if (user != null) {
    setState(() {
      _success = true;
      _userEmail = user.email;
    });
  } else {
    setState(() {
      _success = true;
    });
  }
}