How to get Username of Specific User from Firebase?

Question

I am making a Group chat app in android, where the database is Firebase Realtime DB.

While registering users i successfully managed to save the user's "UserName" and "Email" inside "Users" node in Firebase.

The Question is how to get the Specific person name along with the chat when he/she posts a message ?

Here is my Registration Activity where i saved "Username" and "Email" in DB as a new user registers :

FirebaseAuth mAuth;
 mAuth = FirebaseAuth.getInstance();
     private void DOSignup() {
        final String get_name = name.getText().toString().trim();
        final String get_email = email.getText().toString().trim();
        String get_password = password.getText().toString().trim();

        mAuth.createUserWithEmailAndPassword(get_email, get_password).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {
                if (task.isSuccessful()) {

                    FirebaseUser firebaseUser = mAuth.getCurrentUser();
                    Log.e("Current User", firebaseUser.toString());
                    DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference().child("Users");
                    GetUserName getUserName = new GetUserName(get_name, get_email);
                    String id = databaseReference.push().getKey();
                    databaseReference.child(id).setValue(getUserName);
                    Toast.makeText(getApplicationContext(), "Registration successful!", Toast.LENGTH_LONG).show();
                    Intent intent = new Intent(SignUpActivity.this, LoginActivity.class);
                    startActivity(intent);
                } else {
                    Toast.makeText(getApplicationContext(), "Registration failed! Please try again later", Toast.LENGTH_LONG).show();
                }
            }
        });

This is how the user posts message :

     private void postMessages() {
        databaseReference = FirebaseDatabase.getInstance().getReference("MessageTest");
        Log.e("Reference is : ", String.valueOf(databaseReference));
        String actual_msg = editText.getText().toString().trim();

ChatModel chatModel = new ChatModel(actual_msg);
            String id = databaseReference.push().getKey();
            databaseReference.child(id).setValue(chatModel).addOnCompleteListener(new OnCompleteListener<Void>() {
                @Override
                public void onComplete(@NonNull Task<Void> task) {
                    if (task.isSuccessful()) {
                        Toast.makeText(ChatActivity.this, "Message Sent Successfully", Toast.LENGTH_SHORT).show();
                        editText.setText("");
                    } else {
                        Toast.makeText(ChatActivity.this, "Message Sent Failed !", Toast.LENGTH_SHORT).show();
                    }
                }
            });
        }

Here is my ChatModel Class :

 public class ChatModel {
    String messages;
    public ChatModel() {
    }
    public ChatModel(String messages) {
        this.messages = messages;
    }
    public String getMessages() {
        return messages;
    }
}

Here is my ChatAdapter class, where the Message are shown to users :

public class ChatAdapter extends FirebaseRecyclerAdapter<ChatModel, ChatAdapter.ViewHolder> {
Context context;
List<ChatModel> chatModelList;
public ChatAdapter(@NonNull FirebaseRecyclerOptions<ChatModel> options, Context context, List<ChatModel> chatModelList) {
    super(options);
    this.context = context;
    this.chatModelList = chatModelList;
}
@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.chat_layout,
            parent, false);
    return new ViewHolder(view);
}
@Override
protected void onBindViewHolder(@NonNull ViewHolder holder, int position, @NonNull ChatModel model) {
    ChatModel model1 = chatModelList.get(position);
    GetUserName getUserName = new GetUserName();
    DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference();
    holder.messages.setText();
    holder.userName.setText(databaseReference.getKey());
}
class ViewHolder extends RecyclerView.ViewHolder {
    TextView messages,userName;
    public ViewHolder(@NonNull View itemView) {
        super(itemView);
        messages = itemView.findViewById(R.id.message_body);
        userName = itemView.findViewById(R.id.userName); //This is a TextView where usernames need to be shown 
    }
}

Answer 1

First of all, I'd highly recommend changing the structure of how you store the user data slightly. You're now using push() to generate a unique key. But since each user already has a unique UID, you can store the users under that UID and make looking them up easier. To store it in this structure:

DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference().child("Users");
GetUserName getUserName = new GetUserName(get_name, get_email);
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
databaseReference.child(uid).setValue(getUserName);

With that in place, let's get to using the user name when writing messages to the database.

---

You'll want to load the name of the current user when the app starts and they're signed in. The code for that would look something like this:

if (FirebaseAuth.getInstance().getCurrentUser() != null) {
  String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
  DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference().child("Users");
  DatabaseReference userReference = databaseReference.child(uid);
  userReference.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
      userName = dataSnapshot.child("UserName").getValue(String.class);
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        throw databaseError.toException();
    }
  }
}

In the above snippet userName is a member field on your activity class, so that you can access it other places too.

After this code runs, you can write the user name to the messages by:

1. Adding a property for the user name to your ChatModel class
2. Setting the user name that you loaded with the code snippet, each time you create a ChatModel instance.