MessageActivity.java

package change.com.animationwithsplash;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
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 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 change.com.animationwithsplash.Adapter.MessageAdapter;
import change.com.animationwithsplash.Models.Chats;
import change.com.animationwithsplash.Models.User;

public class MessageActivity extends AppCompatActivity {

    ImageView profile_image;
    TextView username;

    FirebaseUser fuser;
    DatabaseReference reference;

    Intent intent;

    ImageButton btn_send;
    EditText text_send;

    MessageAdapter messageAdapter;
    List<Chats> mChat;
    RecyclerView recyclerView;

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

        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setTitle("");
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        toolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                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 = getIntent();
        final String userid = intent.getStringExtra("userid");
        fuser = FirebaseAuth.getInstance().getCurrentUser();

        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(MessageActivity.this, "You cannot 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());
                profile_image.setImageResource(R.drawable.ic_account3);
                readMessage(fuser.getUid(),userid);
            }

            @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 readMessage(final String myid, final String userid)
    {
        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())
                {
                    Chats chats = snapshot.getValue(Chats.class);
                    if(chats.getReceiver().equals(myid) && chats.getSender().equals(userid) ||
                            chats.getReceiver().equals(userid) && chats.getSender().equals(myid)){
                        mChat.add(chats);
                    }
                    messageAdapter = new MessageAdapter(MessageActivity.this,mChat);
                    recyclerView.setAdapter(messageAdapter);
                }
            }

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

            }
        });
    }
}