java.lang.String com.google.firebase.auth.FirebaseUser.getUid()' on a null object reference

Question

when I am trying to run app it automatically crashing showing an error

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.google.firebase.auth.FirebaseUser.getUid()' on a null object reference at com.example.akhilkumar.chitchat.MainActivity.onCreate(MainActivity.java:55)

error pointing to

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

public class MainActivity extends AppCompatActivity {

    private NavigationView navigationView;
    private DrawerLayout drawerLayout;
    private RecyclerView postList;
    private Toolbar mToolbar;
    private ActionBarDrawerToggle actionBarDrawerToggle;

    private FirebaseAuth mAuth;

    private DatabaseReference userRef;

    private CircleImageView navProfileImage;
    private TextView navProfileUserName;

    String currentUserID;

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



        mAuth = FirebaseAuth.getInstance();


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

        userRef = FirebaseDatabase.getInstance().getReference().child("Users");

/*
        mToolbar = (Toolbar)findViewById(R.id.main_page_toolbar);
        setSupportActionBar(mToolbar);
*/
        getSupportActionBar().setTitle("Home");

        drawerLayout = (DrawerLayout)findViewById(R.id.drawable_layout);
        actionBarDrawerToggle = new ActionBarDrawerToggle(MainActivity.this, drawerLayout, R.string.drawer_open, R.string.drawer_close);
        drawerLayout.addDrawerListener(actionBarDrawerToggle);
        actionBarDrawerToggle.syncState();
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);


        navigationView = (NavigationView)findViewById(R.id.navigation_view);

        View navView = navigationView.inflateHeaderView(R.layout.navigation_header);

        navProfileImage = (CircleImageView)navView.findViewById(R.id.nav_profile_image);
        navProfileUserName =(TextView)navView.findViewById(R.id.nav_user_full_name);



        userRef.child(currentUserID).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot)
            {
                if(dataSnapshot.exists())
                {
                    if(dataSnapshot.hasChild("fullname"))
                    {
                        String fullname = dataSnapshot.child("fullname").getValue().toString();
                        navProfileUserName.setText(fullname);
                    }
                    if(dataSnapshot.hasChild("profileimage"))
                    {
                        String image = dataSnapshot.child("profileimage").getValue().toString();
                        Picasso.get().load(image).placeholder(R.drawable.profile).into(navProfileImage);
                    }
                    else
                    {
                        Toast.makeText(MainActivity.this, "Profile name do not exists...", Toast.LENGTH_SHORT).show();
                    }
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });



        navigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {

                UserMenuSelector(item);


                return false;
            }
        });

    }





    @Override
    protected void onStart() {
        super.onStart();
        FirebaseUser currentUser = mAuth.getCurrentUser();

        if(currentUser == null){
            SendUserToLoginActivity();
        }
        else{
            CheckUserExistence();
        }
    }

    private void CheckUserExistence() {

        final String current_user_id = mAuth.getCurrentUser().getUid();

        userRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot)
            {
                if(!dataSnapshot.hasChild(current_user_id))
                {
                    SendUserToSetupActivity();
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

    }

    private void SendUserToSetupActivity() {

        Intent setupIntent = new Intent(MainActivity.this, SetupActivity.class);
        setupIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
        startActivity(setupIntent);
        finish();

    }

    private void SendUserToLoginActivity() {

        Intent loginIntenet = new Intent(MainActivity.this, LoginActivity.class);
        loginIntenet.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
        startActivity(loginIntenet);
        finish();

    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        if(actionBarDrawerToggle.onOptionsItemSelected(item)){
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    private void UserMenuSelector(MenuItem item) {

        switch (item.getItemId()){


            case R.id.nav_profile:
                Toast.makeText(this,"Profile",Toast.LENGTH_LONG).show();
                break;
            case R.id.nav_home:
                Toast.makeText(this,"Home",Toast.LENGTH_LONG).show();
                break;

            case R.id.nav_friends:
                Toast.makeText(this,"Friends",Toast.LENGTH_LONG).show();
                break;

            case R.id.nav_find_friends:
                Toast.makeText(this,"Find Friends",Toast.LENGTH_LONG).show();
                break;

            case R.id.nav_messages:
                Toast.makeText(this,"Messages",Toast.LENGTH_LONG).show();
                break;

            case R.id.nav_settings:
                Toast.makeText(this,"Settings",Toast.LENGTH_LONG).show();
                break;

            case R.id.nav_logout:

                mAuth.signOut();
                SendUserToLoginActivity();
                Toast.makeText(this,"Logout Successfully",Toast.LENGTH_LONG).show();
                break;

            case R.id.nav_about_app:
                Toast.makeText(this,"About",Toast.LENGTH_LONG).show();
                break;





        }
    }
}

Alex Mamo · Accepted Answer · 2018-07-16T16:52:04.753

4

The following line of code:

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

May produce NullPointerException. So to solve this, you need to check first for nullity. So please use the following lines of code:

FirebaseUser mFirebaseUser = mAuth.getCurrentUser();
if(mFirebaseUser != null) {
    currentUserID = mFirebaseUser.getUid(); //Do what you need to do with the id
}

edited Jul 16 '18 at 16:52

answered Jul 16 '18 at 16:44

Alex Mamo

130,605
17
163
193

Caused by: java.lang.NullPointerException: Can't pass null for argument 'pathString' in child() at com.google.firebase.database.DatabaseReference.child(Unknown Source) at com.example.akhilkumar.chitchat.MainActivity.onCreate(MainActivity.java:87) – Jagdeesh Jul 16 '18 at 16:48
error pointing to userRef.child(currentUserID).addValueEventListener(new ValueEventListener() { – Jagdeesh Jul 16 '18 at 16:51
If you are getting another error, it means the initial problem was solved. As a personal hint, your `currentUserID` object is null but this is basically another question. In order to follow the rules of this comunity, please post another fresh question, so me and other users can help you. – Alex Mamo Jul 16 '18 at 16:58

score 2 · Answer 2 · answered Jul 16 '18 at 16:46

2

You are accessing mAuth in onStart method but you are initializing it in onCreate. So that's why you are getting this error.

So write the following code in onCreate() method

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

    mAuth = FirebaseAuth.getInstance();

    FirebaseUser currentUser = mAuth.getCurrentUser();

    if(currentUser == null){
        SendUserToLoginActivity();
    }
    else{
        CheckUserExistence();
    }
}

answered Jul 16 '18 at 16:46

Raj

2,997
2
12
30

This will resolve your error. – Raj Jul 16 '18 at 16:50
Error Not resolved – Jagdeesh Jul 16 '18 at 16:54
this time error pointing to userRef.child(currentUserID).addValueEventListener(new ValueEventListener() { – Jagdeesh Jul 16 '18 at 16:55
Are u moving to this activity after signing into the app ?? – Raj Jul 16 '18 at 16:57
No, When i run the app at the time app crashing – Jagdeesh Jul 16 '18 at 16:58
It means your currentUserId is null. So you have to first login and then it will fetch that userid. And your app will run perfectly. – Raj Jul 16 '18 at 16:59
@Raj you think a user who asks about a NPE on two consecutive days will upvote you? LOL – Chisko Jul 16 '18 at 17:35
very funny google devs, the documentation tells us to put this in onStrart(), OMG: https://firebase.google.com/docs/auth/android/start?hl=en&authuser=6%2F#check_current_auth_state. anyways, thanks for the simple soultion. – Joseph Ali Jan 03 '23 at 13:51

java.lang.String com.google.firebase.auth.FirebaseUser.getUid()' on a null object reference

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