java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.isEmpty()' on a null object reference

Question

I have a bug in my app and I don't know how to resolve it. When I try to run my app, it just says, unfortunately app has stopped and in the logcat it says this:

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.isEmpty()' on a null object reference' on a null object reference

t is suppose to take the user to the login activity since the user is not logged in. This is the code of the fragment where the error is being pointed to.

package com.app.whatsupafrica;


import android.content.Intent;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import com.firebase.ui.database.FirebaseRecyclerAdapter;
import com.firebase.ui.database.FirebaseRecyclerOptions;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import com.squareup.picasso.Picasso;

import de.hdodenhof.circleimageview.CircleImageView;


/**
* A simple {@link Fragment} subclass.
*/
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.getUid();
    if (mAuth.getUid() == null)
    {
     SendUserToLoginActivity();
    }
    if (! mAuth.getUid().isEmpty())
    {
        ChatsRef = FirebaseDatabase.getInstance().getReference().child("Contacts").child(mAuth.getUid());
    }
    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 v)
                                    {
                                        Intent chatIntent = new Intent(getContext(), ChatActivity.class);
                                        chatIntent.putExtra("visit_user_id", usersIDs);
                                        chatIntent.putExtra("visit_user_name", retName);
                                        chatIntent.putExtra("visit_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);
        userStatus = itemView.findViewById(R.id.user_status);
        userName = itemView.findViewById(R.id.user_profile_name);
    }
}
private void SendUserToLoginActivity()
{
    Intent loginIntent = new Intent(getContext(), LoginActivity.class);
    startActivity(loginIntent);
}
}

Have you tried to place a breakpoint and inspect the reason why it is happening? — bichito, Mar 27 '20 at 15:10
Maybe you should be checking mAuth.getCurrentUser(). If the user is logged out, the user is null and you can't call getUid() on something that is null. Have you tried checking this? — Norik, Mar 27 '20 at 15:14

score 0 · Answer 1 · answered Mar 27 '20 at 15:15

0

Check if the user has signed in or not

 if(! Objects.requireNonNull( mAuth.getUid() ).isEmpty())
     currentUserID = mAuth.getUid();
 else
     //sign in the user

answered Mar 27 '20 at 15:15

Akash Starvin Dsouza

399
3
8

I just tried that. It did not still fix it. Do you know any other thing i can do? – Tomi Tokko Mar 27 '20 at 15:29
Are you sure that the user is logged in? – Akash Starvin Dsouza Mar 27 '20 at 15:34
No, the user is not logged in. Thats why i did this if(! Objects.requireNonNull( mAuth.getUid() ).isEmpty()) currentUserID = mAuth.getUid(); else Intent loginIntent = new Intent(getContext(), LoginActivity.class); startActivity(loginIntent); – Tomi Tokko Mar 27 '20 at 15:42
Can you copy-paste the logcat text or image? – Akash Starvin Dsouza Mar 27 '20 at 15:46
this is it....... Process: com.app.whatsupafrica, PID: 29208 java.lang.NullPointerException: Can't pass null for argument 'pathString' in child() – Tomi Tokko Mar 27 '20 at 15:56
It is because of this line ChatsRef = FirebaseDatabase.getInstance().getReference().child("Contacts").child(currentUserID); since currentUserID is null – Akash Starvin Dsouza Mar 27 '20 at 16:00
So, what do you think i should do – Tomi Tokko Mar 27 '20 at 16:03
Get that reference line inside an if-else statement, if( ! currentUserID.isEmpty) ChatsRef = FirebaseDatabase.getInstance().getReference().child("Contacts").child(currentUserID); – Akash Starvin Dsouza Mar 27 '20 at 16:10
Thank you, i will try that now – Tomi Tokko Mar 27 '20 at 16:13
I just did that, but it did not work. This is the new error in the logcat "java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.isEmpty()' on a null object reference" – Tomi Tokko Mar 27 '20 at 16:32
Its better to use (! mAuth.getUid().isEmpty()) instread of (! currentUserID.isEmpty) – Akash Starvin Dsouza Mar 27 '20 at 16:37
i jaust changed that again and it still gives the same error, which is "java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.isEmpty()' on a null object reference" – Tomi Tokko Mar 27 '20 at 16:44
Please what do i do – Tomi Tokko Mar 27 '20 at 16:53
Can you update your question by copy-pasting all the changes u made in the code ? – Akash Starvin Dsouza Mar 27 '20 at 16:57
okay, i will do that now – Tomi Tokko Mar 27 '20 at 17:10
i have done that.... please take a look at the code and tell me if there is anything i should do – Tomi Tokko Mar 27 '20 at 17:28
Replace currentUserId in the if-else statement to mAuth.getUid(). becasue if user isnt logged in then currentUserId will result in NullPointerException – Akash Starvin Dsouza Mar 27 '20 at 17:36
I have done it.... It is still the same thing – Tomi Tokko Mar 27 '20 at 17:41
please i really need helpurgently – Tomi Tokko Mar 27 '20 at 17:43
Can u update the code again? – Akash Starvin Dsouza Mar 27 '20 at 17:43
i have updated the code again – Tomi Tokko Mar 27 '20 at 17:50
Replace ( == null ) with isEmpty() – Akash Starvin Dsouza Mar 27 '20 at 18:22

score 0 · Answer 2 · answered Mar 27 '20 at 15:29

0

Add this code:

mAuth.getUid();

instead of

mAuth.getCurrentUser().getUid();

Apparently current user is null

answered Mar 27 '20 at 15:29

Kasım Özdemir

5,414
3
18
35

i just tried that, it still says app has stopped. But it brought out a different error. This time it brought out, "java.lang.NullPointerException: Can't pass null for argument 'pathString' in child()" – Tomi Tokko Mar 27 '20 at 15:44
Is the problem solved? – Kasım Özdemir Mar 27 '20 at 20:22

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.isEmpty()' on a null object reference

2 Answers2