Firebase authentication keeps giving a com.google.firebase.auth.FirebaseAuth.getCurrentUser()' on a null object reference

Question

I am trying to implement Firebase authentication for an android app and I keep getting an error. I am new to Android and at best a Java novice so I am sure it is something simple that I am missing. Any suggestions/advice is much appreciated!

Here is my code base:

public class LoginActivity extends AppCompatActivity {

    private static final String TAG = "LoginActivity";

    //Firebase
    private FirebaseAuth mAuth;

    private Context mContext;
    private ProgressBar mProgressBar;
    private EditText mEmail, mPassword;
    private TextView mPleaseWait;


    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);
        mProgressBar = (ProgressBar) findViewById(R.id.progressBar);
        mPleaseWait = (TextView) findViewById(R.id.pleaseWait);
        mEmail = (EditText)findViewById(R.id.input_email);
        mPassword = (EditText) findViewById(R.id.input_password);
        mContext = LoginActivity.this;

        Log.d(TAG, "onCreate: Login started.");
        mPleaseWait.setVisibility(View.GONE);
        mProgressBar.setVisibility(View.GONE);
    }

    private boolean isStringNull(String string){
        Log.d(TAG, "isStringNull: checking if null.");

        if(string.equals("")){
            return true;
        }else {
            return false;
        }
    }

    /**
     * FireBase Code
     *
     */
    private void init(){

        //initialize the button for logging in
        Button btnLogin = (Button) findViewById(R.id.btn_login);
        btnLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Log.d(TAG, "onClick: attempting to login. ");

                String email = mEmail.getText().toString();
                String password = mPassword.getText().toString();

                if (isStringNull(email) && isStringNull(password)){
                    Toast.makeText(mContext, "You must fill out all fields.", Toast.LENGTH_SHORT).show();
                }else{
                    mProgressBar.setVisibility(View.VISIBLE);
                    mPleaseWait.setVisibility(View.VISIBLE);

                    mAuth.signInWithEmailAndPassword(email, password)
                            .addOnCompleteListener(LoginActivity.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, "signInWithEmail:success");

                                        FirebaseUser currentUser = mAuth.getCurrentUser();
                                        updateUI(currentUser);
                                    } else {
                                        // If sign in fails, display a message to the user.
                                        Log.w(TAG, "signInWithEmail:failure", task.getException());

                                        Toast.makeText(LoginActivity.this, "Authentication failed.",
                                                Toast.LENGTH_SHORT).show();
                                        updateUI(null);
                                    }

                                }
                            });
                }

            }
        });
    }
     /**
      * Checks to see if the @param 'user' is logged in.
      */
    private void updateUI(FirebaseUser currentUser) {
        Log.d(TAG, "updateUI: checking if user is logged in.");

        if(currentUser == null){
            Intent intent = new Intent(mContext, LoginActivity.class);
            startActivity(intent);
        }
    }

    @Override
    public void onStart() {
        Log.d(TAG, "onStart: Starting LoginActivity onStart method.");
        super.onStart();

        // Check if user is signed in (non-null) and update UI accordingly.
        FirebaseUser currentUser = mAuth.getCurrentUser();
        updateUI(currentUser);

        if(currentUser != null){
            Log.d(TAG, "onStart:signed_in. " + currentUser);
        }else{
            Log.d(TAG, "onStart:signed_out. ");
        }
    }
}

When I run the code I get the following error message:

D/LoginActivity: onCreate: Login started. onStart: Starting LoginActivity onStart method. D/AndroidRuntime: Shutting down VM.......java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.firebase.auth.FirebaseUser com.google.firebase.auth.FirebaseAuth.getCurrentUser()' on a null object reference

Answer 1

The error message is suggesting that mAuth is null, its default value. You likely never assigned it a value.