When I open an app then it closed and logcat error is return a null pointer. How to solve this error?

Question

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.google.firebase.auth.FirebaseUser.getUid()' on a null object reference at rishabh.example.chatapp.ChatsFragment.onCreateView(ChatsFragment.java:51)

Code of ChatsFragment.java

public class ChatsFragment extends Fragment
{
    private View PrivateChatsView;
    private RecyclerView chatsList;

    private DatabaseReference ChatsRef, UsersRef;
    private FirebaseAuth mAuth;
    private String currentUserID;

    public ChatsFragment() {
        // Required empty public constructor
    }



    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        PrivateChatsView = inflater.inflate(R.layout.fragment_chats, container, false);

        mAuth = FirebaseAuth.getInstance();
        currentUserID = mAuth.getCurrentUser().getUid();
        ChatsRef = FirebaseDatabase.getInstance().getReference().child("Contacts").child(currentUserID);
        UsersRef = FirebaseDatabase.getInstance().getReference().child("Users");

        chatsList = (RecyclerView) PrivateChatsView.findViewById(R.id.chats_list);
        chatsList.setLayoutManager(new LinearLayoutManager(getContext()));

        return PrivateChatsView;
    }

    @Override
    public void onStart()
    {
        super.onStart();

        FirebaseRecyclerOptions<Contacts> options =
                new FirebaseRecyclerOptions.Builder<Contacts>()
                .setQuery(ChatsRef, Contacts.class)
                .build();


        FirebaseRecyclerAdapter<Contacts, ChatsViewHolder> adapter =
                new FirebaseRecyclerAdapter<Contacts, ChatsViewHolder>(options) {
                    @Override
                    protected void onBindViewHolder(@NonNull final ChatsViewHolder holder, int position, @NonNull Contacts model)
                    {
                        final String usersIDs = getRef(position).getKey();
                        final String[] retImage = {"default image"};

                        UsersRef.child(usersIDs).addValueEventListener(new ValueEventListener() {
                            @Override
                            public void onDataChange(@NonNull DataSnapshot dataSnapshot)
                            {
                                if (dataSnapshot.exists())
                                {
                                    if (dataSnapshot.hasChild("image"))
                                    {
                                        retImage[0] = dataSnapshot.child("image").getValue().toString();
                                        Picasso.get().load(retImage[0]).into(holder.profileImage);
                                    }

                                    final String retName = dataSnapshot.child("name").getValue().toString();
                                    final String retStatus = dataSnapshot.child("status").getValue().toString();

                                    holder.userName.setText(retName);
                                    holder.userStatus.setText("Last Seen: " + "\n" + "Date " + " Time");


                                    holder.itemView.setOnClickListener(new View.OnClickListener() {
                                        @Override
                                        public void onClick(View view)
                                        {
                                            Intent chatIntent = new Intent(getContext(), ChatActivity.class);
                                            chatIntent.putExtra("visit_user_id", usersIDs);
                                            chatIntent.putExtra("visit_user_name", retName);
                                            chatIntent.putExtra("visit_user_image", retImage[0]);
                                            startActivity(chatIntent);
                                        }
                                    });
                                }
                            }

                            @Override
                            public void onCancelled(@NonNull DatabaseError databaseError)
                            {

                            }
                        });
                    }

                    @NonNull
                    @Override
                    public ChatsViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i)
                    {
                        View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.users_display_layout, viewGroup, false);
                        return new ChatsViewHolder(view);
                    }
                };

        chatsList.setAdapter(adapter);
        adapter.startListening();
    }

    public static class ChatsViewHolder extends RecyclerView.ViewHolder
    {
        CircleImageView profileImage;
        TextView userStatus, userName;

        public ChatsViewHolder(@NonNull View itemView)
        {
            super(itemView);

            profileImage = itemView.findViewById(R.id.users_profile_image);
            userName = itemView.findViewById(R.id.user_profile_name);
            userStatus = itemView.findViewById(R.id.user_status);
        }
    }
}

I don't know where the code is giving error and could not able to find the bug. Please help me to find the bug.

Error pointing on the line: currentUserID = mAuth.getCurrentUser().getUid();

This line is used in many activities and not given any error but on this activity this line is giving a null error. Please help me so that I can solve this error.

Answer 1

It looks like the current user isn't initialized when your ChatsFragment is created.

1. The simplest fix is to not create the ChatsFragment until the user is initialized.

2. Another simple fix is to only attach the database listener if there is a current user:

    mAuth = FirebaseAuth.getInstance();
    if (mAuth.getCurrentUser() != null) {
        currentUserID = mAuth.getCurrentUser().getUid();
        ChatsRef = FirebaseDatabase.getInstance().getReference().child("Contacts").child(currentUserID);
        UsersRef = FirebaseDatabase.getInstance().getReference().child("Users");
    }
   

3. A common alternative is to wait until the user is initialized inside the ChatsFragment before attaching a listener to the database. You do that with a so-called auth state listener:

    mAuth = FirebaseAuth.getInstance();
    mAuth.onAuthStateChanged(new FirebaseAuth.AuthStateListener() {
        @Override
        public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
            FirebaseUser user = firebaseAuth.getCurrentUser();
            if (user != null) {
                currentUserID = mAuth.getCurrentUser().getUid();
                ChatsRef = FirebaseDatabase.getInstance().getReference().child("Contacts").child(currentUserID);
                UsersRef = FirebaseDatabase.getInstance().getReference().child("Users");
            }
        }
    };