Why doesn't my userid transfer from adapter to messaging activity?

Question

I'm putting a chat feature into an application I'm building in android studio using firebase. I've been following a guide however, I keep getting the NullPointerException error. It's because the intent I'm passing from my user adapter is not passing the extras, or even the intent itself, any idea why this could be?

My code is not assigning my User object an id. When testing the app, I click on a user and the app crashes because the their id doesn't get assigned.

My knowledge of AS isn't good enough to figure out exactly why this is happening. It seems to be occurring in my user adapter and messaging activities.

I assigned my user based on the position in my list of users.

final User user = mUsers.get(position);

Then set it up to be sent to my messaging activity.

holder.itemView.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent intent = new Intent(mContext, ActualMessaging.class);
            intent.putExtra("userid,", user.getId());
            mContext.startActivity(intent);
        }
    });

Once it's there I think this is referencing the code in my useradapter activity

final String userid = intent.getStringExtra("userid");

Then I try to get that specific user id, but the "userid" is returning null.

reference = FirebaseDatabase.getInstance().getReference("Users").child(userid);

If anyone could let me know what I'm doing wrong that would be great, I'll put (what i'm pretty sure are the right bits of code) below.

User Fragment:

package com.example.testandroidapplication.Fragments;

import android.content.Context;
import android.net.Uri;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v4.app.Fragment;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.example.testandroidapplication.Adapter.UserAdapter;
import com.example.testandroidapplication.Model.User;
import com.example.testandroidapplication.R;
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.List;


public class UsersFragment extends Fragment {

    private RecyclerView recyclerView;

    private UserAdapter userAdapter;
    private List<User> mUsers;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View view = inflater.inflate(R.layout.fragment_users, container, false);

        recyclerView = view.findViewById(R.id.recycler_view);
        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));

        mUsers = new ArrayList<>();


        readUsers();

        return view;
    }

    private void readUsers() {
        final FirebaseUser firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
        DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Users");

        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                mUsers.clear();
                for(DataSnapshot snapshot : dataSnapshot.getChildren()){
                    User user = snapshot.getValue(User.class);

                    assert user != null;
                    assert firebaseUser != null;
                    if(!user.getId().equals(firebaseUser.getUid())){
                        mUsers.add(user);
                    }
                }

                userAdapter = new UserAdapter(getContext(), mUsers);
                recyclerView.setAdapter(userAdapter);
            }

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

            }
        });
    }

}

User adaptor

package com.example.testandroidapplication.Adapter;

import android.content.Context;
import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import com.bumptech.glide.Glide;
import com.example.testandroidapplication.ActualMessaging;
import com.example.testandroidapplication.Model.User;
import com.example.testandroidapplication.R;

import java.util.List;

public class UserAdapter extends RecyclerView.Adapter<UserAdapter.ViewHolder> {

    private Context mContext;
    private List<User> mUsers;

    public UserAdapter(Context mContext, List<User> mUsers){

        this.mUsers = mUsers;
        this.mContext = mContext;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(mContext).inflate(R.layout.user_item, parent, false);
        return new UserAdapter.ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {

        //made user final variable, debugging, check back
        final User user = mUsers.get(position);
        holder.username.setText(user.getUsername());

        if(user.getImageURL().equals("default")){
            holder.profile_image.setImageResource(R.mipmap.ic_launcher);
        } else {
            Glide.with(mContext).load(user.getImageURL()).into(holder.profile_image);
        }

        holder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(mContext, ActualMessaging.class);
                intent.putExtra("userid,", user.getId());
                mContext.startActivity(intent);
            }
        });

    }

    @Override
    public int getItemCount() {
        return mUsers.size();
    }

    public class ViewHolder extends RecyclerView.ViewHolder {

        public TextView username;
        public ImageView profile_image;

        public ViewHolder(View itemView) {
            super(itemView);

            username = itemView.findViewById(R.id.username);
            profile_image = itemView.findViewById(R.id.profile_image);
        }
    }
}

User class:

    package com.example.testandroidapplication.Model;

public class User {

    private String id;
    private String username;
    private String imageURL;

    public User(String id, String username, String imageURL) {
        this.id = id;
        this.username = username;
        this.imageURL = imageURL;
    }

    public User(String id, String username) {
        this.id = id;
        this.username = username;
    }

    public User(String id){

        this.id=id;
    }

    public User() {

    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getImageURL() {
        return imageURL;
    }

    public void setImageURL(String imageURL) {
        this.imageURL = imageURL;
    }
}

Actual Messaging:

package com.example.testandroidapplication;

import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.Toast;

import com.bumptech.glide.Glide;
import com.example.testandroidapplication.Adapter.MessageAdapter;
import com.example.testandroidapplication.Model.Chat;
import com.example.testandroidapplication.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;

import de.hdodenhof.circleimageview.CircleImageView;

import static com.google.android.gms.common.internal.safeparcel.SafeParcelable.NULL;

public class ActualMessaging extends AppCompatActivity {

    CircleImageView profile_image;
    TextView username;

    FirebaseUser fuser;
    DatabaseReference reference;

    ImageButton btn_send;
    EditText text_send;

    MessageAdapter messageAdapter;
    List<Chat> mchat;

    RecyclerView recyclerView;


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

        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setTitle("");
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        toolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                finish();
            }
        });

        recyclerView = findViewById(R.id.recycler_view);
        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.username);
        btn_send = findViewById(R.id.btn_send);
        text_send = findViewById(R.id.text_send);

        Intent intent = getIntent();

        final String userid = intent.getStringExtra("userid");

        fuser = FirebaseAuth.getInstance().getCurrentUser();

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

        fuser = FirebaseAuth.getInstance().getCurrentUser();
        reference = FirebaseDatabase.getInstance().getReference("Users").child(userid);

        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

                final User user = dataSnapshot.getValue(User.class);

                try {

                    username.setText(user.getUsername());

                    if (user.getImageURL().equals("default")) {
                        profile_image.setImageResource(R.mipmap.ic_launcher);
                    } else {
                        Glide.with(ActualMessaging.this).load(user.getImageURL()).into(profile_image);
                    }

                    readMessages(fuser.getUid(), userid, user.getImageURL());

                } catch (NullPointerException npe){
                    Toast.makeText(ActualMessaging.this, ("userid: " + userid + "username: " + username.toString()), Toast.LENGTH_SHORT).show();
                }
            }

            @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(ActualMessaging.this, mchat, imageurl);
                recyclerView.setAdapter(messageAdapter);

            }
        }

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

        }
    });
}

}

Error in Logcat

2019-03-11 22:36:47.920 18284-18284/com.example.testandroidapplication E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.testandroidapplication, PID: 18284
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.testandroidapplication/com.example.testandroidapplication.ActualMessaging}: java.lang.NullPointerException: Can't pass null for argument 'pathString' in child()
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
     Caused by: java.lang.NullPointerException: Can't pass null for argument 'pathString' in child()
        at com.google.firebase.database.DatabaseReference.child(com.google.firebase:firebase-database@@16.1.0:101)
        at com.example.testandroidapplication.ActualMessaging.onCreate(ActualMessaging.java:109)
        at android.app.Activity.performCreate(Activity.java:7136)
        at android.app.Activity.performCreate(Activity.java:7127)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:193) 
        at android.app.ActivityThread.main(ActivityThread.java:6669) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at
com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

Thanks for any suggestions.

Possible duplicate of [What is a NullPointerException, and how do I fix it?](https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — m0skit0, Mar 13 '19 at 15:00
"Can't pass null for argument 'pathString' in child()" is pretty clear in my opinion. — m0skit0, Mar 13 '19 at 15:01
Yes that's obvious. I'm asking why it's not getting the user id, not why my code isn't working. — C. Mac, Mar 13 '19 at 15:26

score 0 · Accepted Answer · answered Mar 14 '19 at 02:57

0

Problem: This line make your app does not work as expected.

intent.putExtra("userid,", user.getId());

As you can see, you must use userid instead of userid, with a comma in the end.

Solution: Change your code to

intent.putExtra("userid", user.getId());

answered Mar 14 '19 at 02:57

Son Truong

13,661
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Thank you, thank you thank you. Can't believe it was that simple. Thanks for taking the time to check for me. Appreciate that so much. – C. Mac Mar 15 '19 at 03:10
@C.Mac Glad to hear that. Happy coding :) – Son Truong Mar 15 '19 at 03:16

score 0 · Answer 2 · answered Mar 14 '19 at 07:41

I think you can first check userid is null or not then only you should pass in child() In your case problem is the key you are passing is different and fetching is different so need to fetch the correct key. If you are passing key

intent.putExtra("userid,", user.getId());

Fetching key

String userid = intent.getStringExtra("userid,");

OR You can also create key as constant

public static final USERID="userid"

intent.putExtra(USERID, user.getId());

Fetching key

String userid = intent.getStringExtra(USERID);

This will not create a typo mistake

Going to implement that just now to avoid errors like this in the future. Thanks very much for having a look! — C. Mac, Mar 15 '19 at 03:11

Why doesn't my userid transfer from adapter to messaging activity?

2 Answers2