Can't pass null for argument 'pathString' in child() When i try to open the activity (app crashed)

Question

I am trying to read some data from firebase database, and when i try to open the activity to see the result i get this error: Caused by: java.lang.NullPointerException: Can't pass null for argument 'pathString' in child() The error is poiting me to the first line of this code

reference = FirebaseDatabase.getInstance().getReference("Users").child(userid);
        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                User user = dataSnapshot.getValue(User.class);
                username.setText(user.getUsername());
            }

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

            }

your userid is null, try to move declaration of "String userid" in member class. — koding, Jan 10 '20 at 15:10
If the exception is referring to the line of code you're showing here, `userid` is definitely null. That's not valid. You need to check that before using it like this. — Doug Stevenson, Jan 10 '20 at 16:03

score 0 · Answer 1 · answered Jan 10 '20 at 15:33

package com.example.aplicatiepentrumesagerie;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.Toolbar;

import com.example.aplicatiepentrumesagerie.Model.Chat;
import com.example.aplicatiepentrumesagerie.Model.User;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
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 java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

public class MesajActivity extends AppCompatActivity {

    ImageView profile_image;
    TextView username;

    FirebaseUser fuser;
    DatabaseReference reference;

    ImageButton btn_send;
    EditText text_send;

    MessageAdapter messageAdapter;
    List<Chat>mchat;
    RecyclerView recyclerView;

    Intent intent;


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


        recyclerView = findViewById(R.id.recycler_view1);
        recyclerView.setHasFixedSize(true);
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getApplicationContext());
        linearLayoutManager.setStackFromEnd(true);
        recyclerView.setLayoutManager(linearLayoutManager);

        profile_image = findViewById(R.id.profile_image);
        username = findViewById(R.id.usernamefirebase);

        intent = getIntent();

        final String userid = intent.getStringExtra("userid");
        fuser = FirebaseAuth.getInstance().getCurrentUser();
        btn_send = findViewById(R.id.btn_send);
        text_send = findViewById(R.id.text_send);


        btn_send.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String msg = text_send.getText().toString();
                if(!msg.equals("")){
                    sendMessage(fuser.getUid(), userid, msg);
                }else {
                    Toast.makeText(MesajActivity.this, "You can't send empty message", Toast.LENGTH_SHORT).show();
                }
                text_send.setText("");
            }
        });

        reference = FirebaseDatabase.getInstance().getReference("Users").child(userid);
        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                User user = dataSnapshot.getValue(User.class);
                username.setText(user.getUsername());
            }

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

            }
        });
    }

    private void  sendMessage(String sender, String receiver, String message){
        DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
        HashMap<String, Object>hashMap = new HashMap<>();
        hashMap.put("sender", sender);
        hashMap.put("receiver", receiver);
        hashMap.put("message", message);

        reference.child("Chats").push().setValue(hashMap);
    }
    private void readMessages(final String myid, final String userid, final String imageurl){
        mchat = new ArrayList<>();
        reference = FirebaseDatabase.getInstance().getReference("Chats");
        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                mchat.clear();
                for(DataSnapshot snapshot: dataSnapshot.getChildren()){
                    Chat chat = snapshot.getValue(Chat.class);
                    if(chat.getReceiver().equals(myid) && chat.getSender().equals(userid) ||
                        chat.getReceiver().equals(userid) && chat.getSender().equals(myid)){
                        mchat.add(chat);
                    }
                    messageAdapter = new MessageAdapter(MesajActivity.this, mchat, imageurl);
                    recyclerView.setAdapter(messageAdapter);


                }
            }

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

            }
        });
    }

    public void citeste(View view) {
    }
}

the userid in the clickListener method is working fine. It's successfully adding text in the database — Irimia Ioan, Jan 10 '20 at 15:36

Can't pass null for argument 'pathString' in child() When i try to open the activity (app crashed)

1 Answers1