How to detect firebase user registration and signIn successfully in flutter - firebase

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;
});
}
}