Test whether this is the first time the facebook login was called with firebase

Question

For the email and password authentication in firebase we have both "register" and "log in" functions, but for the log in with Facebook we only have the login(or am i'm wrong?)
I'm trying to determine whether this is the first time the user have connected to the application with this facebook account, and if so, add it to the database as well.

this is my current code, becuase firebase is an async database, this mechanizem does not work

@Override
protected void onCreate (Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main_customer);

    mLoginButton = (LoginButton) findViewById(R.id.login_button);
    mLoginButton.setVisibility(View.GONE);

    mCallbackManager = CallbackManager.Factory.create();
    mLoginButton.setReadPermissions("email", "public_profile");
    mLoginButton.registerCallback(mCallbackManager, new FacebookCallback<LoginResult>() {
        @Override
        public void onSuccess(LoginResult loginResult) {
            handleFacebookAccessToken(loginResult.getAccessToken());
            Toast.makeText(MainCustomerActivity.this, "Login Success", Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onCancel() {
            Toast.makeText(MainCustomerActivity.this, "Cancelled", Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onError(FacebookException error) {
            Log.d(TAG, error.toString());
            Toast.makeText(MainCustomerActivity.this, "Error!", Toast.LENGTH_SHORT).show();
        }
    });

    private void handleFacebookAccessToken (AccessToken token) {
        Log.d(TAG, "handleFacebookAccessToken:" + token);

        AuthCredential credential = FacebookAuthProvider.getCredential(token.getToken());
        mAuth.signInWithCredential(credential)
            .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                @Override
                public void onComplete(@NonNull Task<AuthResult> task) {
                    if (task.isSuccessful()) {
                        // Sign in success, update UI with the signed-in user's information
                        Log.d(TAG, "signInWithCredential:success");
                        currentUser = mAuth.getCurrentUser();
                        testRegisterNewUser();
                        updateUI();
                    } else {
                        // If sign in fails, display a message to the user.
                        Log.w(TAG, "signInWithCredential:failure", task.getException());
                        Toast.makeText(MainCustomerActivity.this, "Authentication failed.",
                                Toast.LENGTH_SHORT).show();
                        //TODO: HANDLE BAD LOGIN
                    }
                    // ...
                }
            });
    }

    private void testRegisterNewUser () {
        String uid = currentUser.getUid();

        mDatabase = FirebaseDatabase.getInstance().getReference().child("Users").child(uid);
        mDatabase.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                testRegisterUserName = (String) dataSnapshot.getValue();

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

        //this is where I want to find whether this uid is already in the database
        if (testRegisterUserName != null) {
            return;
        } else {
            //this is where I want to store to the database

Can I somehow query the handleFacebookAccessToken to determine if it's the first time the user logged in to the server?

Answer 1

You can use the API isNewUser() for when the sign in process is complete. See the docs.

Returns whether the user is new or existing.

So your code (only the onComplete part) would look like this now:

public void onComplete(@NonNull Task<AuthResult> task) {
    if (task.isSuccessful()) {
        // Sign in success, update UI with the signed-in user's information
        Log.d(TAG, "signInWithCredential:success");
        currentUser = mAuth.getCurrentUser();
        boolean isNewUser = task.getResult().getAdditionalUserInfo().isNewUser();
        if(isNewUser){
              testRegisterNewUser();
        }
        updateUI();
    } else {
        // If sign in fails, display a message to the user.
        Log.w(TAG, "signInWithCredential:failure", task.getException());
        Toast.makeText(MainCustomerActivity.this, "Authentication failed.",
                Toast.LENGTH_SHORT).show();
        //TODO: HANDLE BAD LOGIN
    }
    // ...
}