Check if given email exists

问题

Is there a way to know if the email entered by user is real in Firebase? Does the built-in sign up with email&password method have this feature?

EDIT: sorry for the misunderstanding . I don't care if the email has been used before , what I need to know is: if the entered email is 'made-up' or 'real , exists'

回答1:

Yes, you can do that either you create new account or signing in:

For creating, read createUserWithEmailAndPassword's Docs

createUserWithEmailAndPassword throws 3 exceptions:

1. FirebaseAuthWeakPasswordException: if the password is not strong enough

2. FirebaseAuthInvalidCredentialsException: if the email address is malformed

3. FirebaseAuthUserCollisionException: if there already exists an account with the given email address.

You can handle that in onCompleteListener or onFailureListener

Here an example where mAuth is FirebaseAuth instance:

mAuth.createUserWithEmailAndPassword(email, password)
            .addOnCompleteListener(
                    new OnCompleteListener<AuthResult>()
                    {
                        @Override
                        public void onComplete(@NonNull Task<AuthResult> task)
                        {
                            if (!task.isSuccessful())
                            {
                                try
                                {
                                    throw task.getException();
                                }
                                // if user enters wrong email.
                                catch (FirebaseAuthWeakPasswordException weakPassword)
                                {
                                    Log.d(TAG, "onComplete: weak_password");

                                    // TODO: take your actions!
                                }
                                // if user enters wrong password.
                                catch (FirebaseAuthInvalidCredentialsException malformedEmail)
                                {
                                    Log.d(TAG, "onComplete: malformed_email");

                                    // TODO: Take your action
                                }
                                catch (FirebaseAuthUserCollisionException existEmail)
                                {
                                    Log.d(TAG, "onComplete: exist_email");

                                    // TODO: Take your action
                                }
                                catch (Exception e)
                                {
                                    Log.d(TAG, "onComplete: " + e.getMessage());
                                }
                            }
                        }
                    }
            );

For signing in, read signInWithEmailAndPassword's Docs first.

signInWithEmailAndPassword throws two exceptions:

1. FirebaseAuthInvalidUserException: if email doesn't exist or disabled.
2. FirebaseAuthInvalidCredentialsException: if password is wrong

Here is an example:

mAuth.signInWithEmailAndPassword(email, password)
            .addOnCompleteListener(
                    new OnCompleteListener<AuthResult>()
                    {
                        @Override
                        public void onComplete(@NonNull Task<AuthResult> task)
                        {
                            if (!task.isSuccessful())
                            {
                                try
                                {
                                    throw task.getException();
                                }
                                // if user enters wrong email.
                                catch (FirebaseAuthInvalidUserException invalidEmail)
                                {
                                    Log.d(TAG, "onComplete: invalid_email");

                                    // TODO: take your actions!
                                }
                                // if user enters wrong password.
                                catch (FirebaseAuthInvalidCredentialsException wrongPassword)
                                {
                                    Log.d(TAG, "onComplete: wrong_password");

                                    // TODO: Take your action
                                }
                                catch (Exception e)
                                {
                                    Log.d(TAG, "onComplete: " + e.getMessage());
                                }
                            }
                        }
                    }
            );

回答2:

There is another solution without any create user or sign in processes.

//check email already exist or not.
    firebaseAuth.fetchSignInMethodsForEmail(email)
            .addOnCompleteListener(new OnCompleteListener<SignInMethodQueryResult>() {
                @Override
                public void onComplete(@NonNull Task<SignInMethodQueryResult> task) {

                    boolean isNewUser = task.getResult().getSignInMethods().isEmpty();

                    if (isNewUser) {
                        Log.e("TAG", "Is New User!");
                    } else {
                        Log.e("TAG", "Is Old User!");
                    }

                }
            });

回答3:

This maybe late answer but just for someone passing by could get benefit from the answer. I think the best way to check if the email is exist or not is to send the verification email to the inputing email.

Try checking out this link

https://firebase.googleblog.com/2017/02/email-verification-in-firebase-auth.html

Firebase has provided really easy way to verify user email.

回答4:

It would be almost impossible to check if the email entered exists, you can however check if the email string entered conforms to the valid email structure:

if(!isValidEmail(etEmail.getText().toString())) {
         Toast.makeText(getActivity(), "Invalid input for email", Toast.LENGTH_LONG).show();

Then like Jin Liu suggests, use the sendEmailVerification(), like:

 mFirebaseUser.sendEmailVerification().addOnCompleteListener(new OnCompleteListener<Void>() {
            @Override
            public void onComplete(@NonNull Task<Void> task) {
                if(task.isSuccessful())
                Toast.makeText(getContext(), "Email Verfication Sent", Toast.LENGTH_LONG).show();
                else {
                    try{
                        throw task.getException();
                    }catch (Exception e) {

                        Toast.makeText(getContext(), e.getMessage(), Toast.LENGTH_LONG).show();
                    }

                }
            }
        });

来源：https://stackoverflow.com/questions/40093781/check-if-given-email-exists