Keep User logged in Java Firebase

Question

I am trying to keep the user logged into my chat app even after they close the app. So the only way they will be logged out of their account is if they click the log out button.

So far the user does stayed logged in but when I click the log out button, the app crashes. This is the error I get

 Attempt to invoke virtual method 'java.lang.String com.google.firebase.auth.FirebaseUser.getUid()' on a null object reference
    at com.example.chatterbox.ChatsFragment.onCreateView(ChatsFragment.java:54)

the problem is that that error is from a different file. Can someone please help me ?

public class LoginActivity extends AppCompatActivity {

private FirebaseAuth mAuth;
private ProgressDialog loadingBar;

private Button LoginButton ;
private EditText UserEmail, UserPassword;
private TextView NeedNewAccountLink, ForgetPasswordLink;

private DatabaseReference UsersRef;

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

    RelativeLayout relativeLayout = findViewById(R.id.layout);
    AnimationDrawable animationDrawable = (AnimationDrawable) relativeLayout.getBackground();
    animationDrawable.setEnterFadeDuration(5000);
    animationDrawable.setExitFadeDuration(5000);
    animationDrawable.start();

    mAuth = FirebaseAuth.getInstance();
    UsersRef = FirebaseDatabase.getInstance().getReference().child("Users");

    InitializeFields();

    if (UsersRef != null) {

        Intent intent = new Intent(LoginActivity.this, MainActivity.class);
        startActivity(intent);
        finish();

    }

        NeedNewAccountLink.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                SendUserToRegisterActivity();

            }
        });


        LoginButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                AllowUserToLogin();
            }
        });

    }

    private void AllowUserToLogin () {

        String email = UserEmail.getText().toString();
        String password = UserPassword.getText().toString();

        if (TextUtils.isEmpty(email)) {

            Toast.makeText(this, "Please enter your email", Toast.LENGTH_SHORT).show();
        }

        if (TextUtils.isEmpty(password)) {

            Toast.makeText(this, "Please enter your password", Toast.LENGTH_SHORT).show();
        } else {

            loadingBar.setTitle("Logging In");
            loadingBar.setMessage("Please wait...");
            loadingBar.setCanceledOnTouchOutside(true);
            loadingBar.show();

            mAuth.signInWithEmailAndPassword(email, password)
                    .addOnCompleteListener(new OnCompleteListener<AuthResult>() {
                        @Override
                        public void onComplete(@NonNull Task<AuthResult> task) {

                            if (task.isSuccessful()) {

                                String currentUserId = mAuth.getCurrentUser().getUid();
                                String deviceToken = FirebaseInstanceId.getInstance().getToken();

                                UsersRef.child(currentUserId).child("device_token")
                                        .setValue(deviceToken)
                                        .addOnCompleteListener(new OnCompleteListener<Void>() {
                                            @Override
                                            public void onComplete(@NonNull Task<Void> task) {

                                                if (task.isSuccessful()) {

                                                    SendUserToMainActivity();
                                                    Toast.makeText(LoginActivity.this, "Logged in successfully", Toast.LENGTH_SHORT).show();
                                                    loadingBar.dismiss();

                                                }
                                            }
                                        });
                            } else {

                                String message = task.getException().toString();
                                Toast.makeText(LoginActivity.this, "Error:" + message, Toast.LENGTH_SHORT).show();
                                loadingBar.dismiss();

                            }
                        }
                    });

        }

    }

    private void InitializeFields () {

        LoginButton = (Button) findViewById(R.id.login_button);
        UserEmail = (EditText) findViewById(R.id.login_email);
        UserPassword = (EditText) findViewById(R.id.login_password);
        NeedNewAccountLink = (TextView) findViewById(R.id.need_new_account_link);
        ForgetPasswordLink = (TextView) findViewById(R.id.forget_password_link);
        loadingBar = new ProgressDialog(this);

    }

    private void SendUserToMainActivity () {

        Intent mainIntent = new Intent(LoginActivity.this, MainActivity.class);
        mainIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
        startActivity(mainIntent);
        finish();
    }
    private void SendUserToRegisterActivity () {

        Intent registerIntent = new Intent(LoginActivity.this, RegisterActivity.class);
        startActivity(registerIntent);
    }

Error line :

    currentUserID = mAuth.getCurrentUser().getUid();

This is how I check if the user is logged in. If they are I send them to the MainActivity. If they are not they stay on the LoginActivity

if (UsersRef != null) {

        Intent intent = new Intent(LoginActivity.this, MainActivity.class);
        startActivity(intent);
        finish();

    }

You can also check **[this](https://stackoverflow.com/questions/50885891/one-time-login-in-app-firebaseauth)** out. — Alex Mamo, May 20 '19 at 11:54

score 0 · Answer 1 · answered May 18 '19 at 17:59

0

Use addOnSuccessListener instead of addOnCompleteListener

auth.signInWithEmailAndPassword(mEmail, mPassword)
          .addOnSuccessListener(LoginActivity.this, new OnSuccessListener<AuthResult>(){

                    @Override
                    public void onsuccess(@NonNull AuthResult authResult){
                         //your code goes here
                    }
                 });

answered May 18 '19 at 17:59

Erik

5,039
10
63
119

Now both of my `task` is coming up red – May 18 '19 at 18:09
The [addOnSuccessListener](https://developer.android.com/reference/com/google/android/play/core/tasks/OnSuccessListener) will only be called when User is signed in successfully – Erik May 18 '19 at 18:22
Ok but in my LoginActivity file my two task come up as red – May 18 '19 at 18:26

score 0 · Accepted Answer · answered May 19 '19 at 01:43

0

You call

mAuth = FirebaseAuth.getInstance();
UsersRef = FirebaseDatabase.getInstance().getReference().child("Users");

and then

if (UsersRef != null) {
  //do something
}

It's a bit odd because you need to know if there's currently a valid user logged in Firebase. This snippet maybe can be useful:

FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
if (user != null) {
// User is signed in
} else {
// No user is signed in
}

But you're checking if the variable UsersRef (that is a DatabaseReference, i guess) is null or not... Indeed you just gived it a value!!!

answered May 19 '19 at 01:43

Federico Provenziani

161
11

`FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();` – May 19 '19 at 01:48
Should I put that instead of `mAuth = FirebaseAuth.getInstance(); UsersRef = FirebaseDatabase.getInstance().getReference().child("Users");` – May 19 '19 at 01:48
This is my database Ref `private DatabaseReference UsersRef;` – May 19 '19 at 01:49
Yes, i'm suggesting to change your condition. You have to ask if there's a user logged in Firebase, not if there's a DatabaseReference that you have just instanstiated. – Federico Provenziani May 19 '19 at 01:56
I just tried and when I sign in and close the app I got back to the LoginActivity. – May 19 '19 at 01:59
Is it all suppose to be in the onCreate method ? – May 19 '19 at 01:59

Keep User logged in Java Firebase

2 Answers2