How to Implement Pagination in Android RecyclerView using Volley?

package org.geeksforgeeks.demo;

public class UserModal {
    private String firstName;
    private String lastName;
    private String email;
    private String avatar;

    // Constructor
    public UserModal(String firstName, String lastName, String email, String avatar) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
        this.avatar = avatar;
    }

    // Getter and Setter methods
    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getAvatar() {
        return avatar;
    }

    public void setAvatar(String avatar) {
        this.avatar = avatar;
    }
}

package org.geeksforgeeks.demo;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import androidx.recyclerview.widget.RecyclerView;

import com.bumptech.glide.Glide;

import java.util.ArrayList;

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

    // variable for our array list and context.
    private ArrayList<UserModal> userModalArrayList;
    private Context context;

    // creating a constructor.
    public UserRVAdapter(ArrayList<UserModal> userModalArrayList, Context context) {
        this.userModalArrayList = userModalArrayList;
        this.context = context;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        // inflating our layout file on below line.
        View view = LayoutInflater.from(context).inflate(R.layout.user_rv_item, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        // getting data from our array list in our modal class.
        UserModal userModal = userModalArrayList.get(position);

        // on below line we are setting data to our text view.
        holder.firstNameTV.setText(userModal.getFirstName());
        holder.lastNameTV.setText(userModal.getLastName());
        holder.emailTV.setText(userModal.getEmail());

        // on below line we are loading our image
        // from url in our image view using glide.
        Glide.with(context).load(userModal.getAvatar()).into(holder.userIV);
    }

    @Override
    public int getItemCount() {
        // returning the size of array list.
        return userModalArrayList.size();
    }

    public class ViewHolder extends RecyclerView.ViewHolder {
        // creating a variable for our text view and image view.

        // initializing our variables.
        TextView firstNameTV, lastNameTV, emailTV;
        ImageView userIV;

        public ViewHolder(View itemView) {
            super(itemView);
            firstNameTV = itemView.findViewById(R.id.idTVFirstName);
            lastNameTV = itemView.findViewById(R.id.idTVLastName);
            emailTV = itemView.findViewById(R.id.idTVEmail);
            userIV = itemView.findViewById(R.id.idIVUser);
        }
    }
}

package org.geeksforgeeks.demo;

import android.os.Bundle;
import android.view.View;
import android.widget.ProgressBar;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import com.android.volley.Request;
import com.android.volley.toolbox.JsonObjectRequest;
import com.android.volley.toolbox.Volley;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

    // creating variables for array list, adapter, recycler view and progress bar
    private ArrayList<UserModal> userModalArrayList;
    private UserRVAdapter userRVAdapter;
    private RecyclerView userRV;
    private ProgressBar loadingPB;

    // variables for pagination
    private int page = 1;
    
    // limit as per API
    private final int limit = 2; 
    
    // to prevent multiple simultaneous requests
    private boolean isLoading = false; 

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

        // initializing the array list and views
        userModalArrayList = new ArrayList<>();
        userRV = findViewById(R.id.idRVUsers);
        loadingPB = findViewById(R.id.idPBLoading);

        // initializing adapter and setting layout
        // manager and adapter to recycler view
        userRVAdapter = new UserRVAdapter(userModalArrayList, this);
        userRV.setLayoutManager(new LinearLayoutManager(this));
        userRV.setAdapter(userRVAdapter);

        // fetching the first page of data
        getDataFromAPI(page);

        // adding scroll listener to recycler view for pagination
        userRV.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);

                // checking if we have reached the bottom and not already loading
                if (!recyclerView.canScrollVertically(1) && !isLoading && page <= limit) {
                    // showing progress bar, incrementing page, and fetching next page
                    loadingPB.setVisibility(View.VISIBLE);
                    page++;
                    getDataFromAPI(page);
                }
            }
        });
    }

    private void getDataFromAPI(int page) {
        
        // if requested page exceeds limit, show message and return
        if (page > limit) {
            Toast.makeText(this, "That's all the data..", Toast.LENGTH_SHORT).show();
            loadingPB.setVisibility(View.GONE);
            return;
        }

        // setting loading flag to true
        isLoading = true;

        // constructing API URL
        String url = "https://reqres.in/api/users?page=" + page;

        // creating request queue
        var queue = Volley.newRequestQueue(this);

        // creating JSON request
        JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(
                Request.Method.GET, url, null,
                response -> {
                    try {
                        // extracting data array from JSON response
                        JSONArray dataArray = response.getJSONArray("data");

                        // looping through array and adding to model list
                        for (int i = 0; i < dataArray.length(); i++) {
                            JSONObject jsonObject = dataArray.getJSONObject(i);
                            userModalArrayList.add(new UserModal(
                                    jsonObject.getString("first_name"),
                                    jsonObject.getString("last_name"),
                                    jsonObject.getString("email"),
                                    jsonObject.getString("avatar")
                            ));
                        }

                        // notifying adapter about new data
                        userRVAdapter.notifyDataSetChanged();

                        // hiding progress bar and resetting loading state
                        loadingPB.setVisibility(View.GONE);
                        isLoading = false;

                    } catch (JSONException e) {
                        e.printStackTrace();
                        loadingPB.setVisibility(View.GONE);
                        isLoading = false;
                    }
                },
                error -> {
                    // handling error
                    Toast.makeText(MainActivity.this, "Fail to get data..", Toast.LENGTH_SHORT).show();
                    loadingPB.setVisibility(View.GONE);
                    isLoading = false;
                });

        // adding request to queue
        queue.add(jsonObjectRequest);
    }
}