How to check "user email already exists" in firebase using Android Studio

Question

I'm trying to change my code. But, its failed. My output still the same. Which is, if the user put an email that is already exist or not already exist. The validation "This email has been registered." still came out. Why? Can someone whats wrong with my coding?

Here are my method:-

public boolean isCheckEmail(final String email)
{
    mAuth.fetchProvidersForEmail(email).addOnCompleteListener(new OnCompleteListener<ProviderQueryResult>()
    {
        @Override
        public void onComplete(@NonNull Task<ProviderQueryResult> task)
        {
            boolean check = !task.getResult().getProviders().isEmpty();

            if(check)
            {
                Toast.makeText(Signup.this, "This email has been registered.", Toast.LENGTH_SHORT).show();
            }

            else
            {
                Toast.makeText(Signup.this, "This email has been registered.", Toast.LENGTH_SHORT).show();
            }
        }
    });
    return true;
}

While this half coding, I'm trying to call back the method isCheckEmail:-

 private void RegisterAccount(String firstname, String lastname, String email, String password, String confirmpass)
{
    if (TextUtils.isEmpty(email))
    {
        Toast.makeText(Signup.this, "Enter your email address.", Toast.LENGTH_SHORT).show();
    }

    else if (!isValidEmail(email)) {
        Toast.makeText(Signup.this,"Please enter your valid email address.",Toast.LENGTH_SHORT).show();
    }

    else if (!isCheckEmail(email))
    {
        Toast.makeText(Signup.this, "This email has been registered.", Toast.LENGTH_SHORT).show();
    }

Answer 1

fetchProvidersForEmail is an async call so you have to make use of its return value with the callback.

return true on the main thread will not work.

Here is the solution :

First Create an interface with the method (success)

public interface OnEmailCheckListener(){
 void onSuccess(boolean isRegistered);
} 

Your checkEmail Method should be like this:

public void isCheckEmail(final String email,final OnEmailCheckListener listener){
mAuth.fetchProvidersForEmail(email).addOnCompleteListener(new OnCompleteListener<ProviderQueryResult>()
{
    @Override
    public void onComplete(@NonNull Task<ProviderQueryResult> task)
    {
        boolean check = !task.getResult().getProviders().isEmpty();
        
        listener.onSuccess(check);
     
    }
});

}

Finally call your isCheckEmail like this :

isCheckEmail("yourEmail@test.com",new OnEmailCheckListener(){
   @Override
   void onSuccess(boolean isRegistered){
    
     if(isRegistered){
           //The email was registered before
    } else {
           //The email not registered before
    }

   }
});

Hope this helps you.

Answer 2

this method works to check either email existed or not

 void checkEmailExistsOrNot(){
    firebaseauth.fetchSignInMethodsForEmail(email.getText().toString()).addOnCompleteListener(new OnCompleteListener<SignInMethodQueryResult>() {
        @Override
        public void onComplete(@NonNull Task<SignInMethodQueryResult> task) {
            Log.d(TAG,""+task.getResult().getSignInMethods().size());
            if (task.getResult().getSignInMethods().size() == 0){
                // email not existed
            }else {
                // email existed
            }

        }
    }).addOnFailureListener(new OnFailureListener() {
        @Override
        public void onFailure(@NonNull Exception e) {
            e.printStackTrace();
        }
    });
}

Answer 3

Firebase automatically tells you if an email that you want to create an account with already exists. When creating an account you should check if the task was succesfull and under

if(task.isSuccessful()) {} // you have this code in your last bit of code
else{}                     // you have this in your code already

(

you currently have the code

Toast.makeText(getApplicationContext(), "registration not performed", Toast.LENGTH_SHORT).show();

( it is pretty much the last line in the code you provided) but you should replace it with:

try {
    throw task.getException();
} catch(FirebaseAuthUserCollisionException e) {
    // email already in use
Toast.makeText(getApplicationContext(), "Email already taken!", Toast.LENGTH_SHORT).show();
}

So you do not need to check if an email exists yourself because Firebase will automatically throw an exception and then you can for example display a toast.

Answer 4

Kotlin version of Sai Gopi Me's answer

fun checkEmailExistsOrNot() {

        FirebaseAuth
        .getInstance()
        .fetchSignInMethodsForEmail(binding.etEmail.value())
        .addOnCompleteListener { task ->

            Log.d(TAG, "" + task.result?.signInMethods?.size)

            if (task.result?.signInMethods?.size === 0) {
                // email not existed
                Log.d(TAG, "email  not existed")
            } else {
                // email existed
                Log.d(TAG, "checkEmailExistsOrNot: ")

            }
        }.addOnFailureListener {
                e -> e.printStackTrace()
        }

}