Pagination in RecyclerView

1/  Create A New Project  and Implement those Library 

// retrofit2
implementation("com.squareup.retrofit2:retrofit:2.11.0")
implementation("com.squareup.retrofit2:converter-gson:2.11.0")
//glide
implementation("com.github.bumptech.glide:glide:4.16.0")
annotationProcessor("com.github.bumptech.glide:compiler:4.12.0")

// paging3
implementation( "androidx.paging:paging-runtime:3.1.1")

2/  Use that permission

<uses-permission android:name="android.permission.INTERNET"/>

3/  Create item_product xml 

<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="8dp">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        android:padding="8dp">

        <ImageView
            android:id="@+id/product_thumbnail"
            android:layout_width="match_parent"
            android:layout_height="200dp"
            android:scaleType="centerCrop" />

        <TextView
            android:id="@+id/product_title"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textStyle="bold"
            android:textSize="18sp"
            android:paddingTop="8dp" />

        <TextView
            android:id="@+id/product_description"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:paddingTop="4dp" />
        <TextView
            android:id="@+id/product_price"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textStyle="bold"
            android:paddingTop="8dp" />
    </LinearLayout>
</androidx.cardview.widget.CardView>

4/  Main xml 

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/recyclerView"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />

        <ProgressBar
            android:id="@+id/progressBar"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"


            />

    </LinearLayout>

    <ProgressBar
        android:id="@+id/progressBar2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:layout_alignParentBottom="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentRight="true"

        />

</RelativeLayout>

5/New Product Model class

package com.example.paginexample;

public class Product {
    private int id;
    private String title;
    private String description;
    private double price;
    private String thumbnail;

    // Getters
    public int getId() {
        return id;
    }

    public String getTitle() {
        return title;
    }

    public String getDescription() {
        return description;
    }

    public double getPrice() {
        return price;
    }

    public String getThumbnail() {
        return thumbnail;
    }
}

6/  A ProductResponse java class

package com.example.paginexample;

import java.util.List;

public class ProductResponse {
    private List<Product> products;
    private int total;
    private int skip;
    private int limit;

    public List<Product> getProducts() {
        return products;
    }
}

7/  Retrofit Client java class

package com.example.paginexample;

import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

public class RetrofitClient {

    private static Retrofit retrofit = null;

    public static ApiService getApiService() {
        if (retrofit == null) {
            retrofit = new Retrofit.Builder()
                    .baseUrl("https://dummyjson.com/")
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
        }
        return retrofit.create(ApiService.class);
    }
}

8/ Api Service Interface 

package com.example.paginexample;

import retrofit2.Call;
import retrofit2.http.GET;
import retrofit2.http.Query;

public interface ApiService {
    @GET("products")
    Call<ProductResponse> getProducts(@Query("limit") int limit, @Query("skip") int skip);
}

9/  Add ProductAdapter Adapter class

package com.example.splashscreen;

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.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import com.bumptech.glide.Glide;
import java.util.ArrayList;
import java.util.List;


public class ProductAdapter extends RecyclerView.Adapter<ProductAdapter.ProductViewHolder> {
    private List<Product> products = new ArrayList<>();
    private Context context;

    public ProductAdapter(Context context) {
        this.context = context;
    }

    public void addProducts(List<Product> newProducts) {
        products.addAll(newProducts);
        notifyDataSetChanged();
    }

    @NonNull
    @Override
    public ProductViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_product, parent, false);
        return new ProductViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull ProductViewHolder holder, int position) {
        Product product = products.get(position);
        holder.titleTextView.setText(product.getTitle());
        holder.descriptionTextView.setText(product.getDescription());
        holder.priceTextView.setText("$" + product.getPrice());
        Glide.with(context).load(product.getThumbnail()).into(holder.thumbnailImageView);
    }

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

    public static class ProductViewHolder extends RecyclerView.ViewHolder {
        TextView titleTextView, descriptionTextView, priceTextView;
        ImageView thumbnailImageView;

        public ProductViewHolder(@NonNull View itemView) {
            super(itemView);
            titleTextView = itemView.findViewById(R.id.product_title);
            descriptionTextView = itemView.findViewById(R.id.product_description);
            priceTextView = itemView.findViewById(R.id.product_price);
            thumbnailImageView = itemView.findViewById(R.id.product_thumbnail);
        }
    }
}

10/  Java Main Activity

package com.example.paginexample;

import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.widget.ProgressBar;

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

import java.util.List;

import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;

public class MainActivity extends AppCompatActivity {

    private RecyclerView recyclerView;
    private ProgressBar progressBar ;
     ProgressBar progressBar2 ;
    private ProductAdapter productAdapter;
    private int limit = 10;
    private int skip = 0;
    private boolean isLoading = false;

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

        recyclerView = findViewById(R.id.recyclerView);
        progressBar = findViewById(R.id.progressBar);
        progressBar2 = findViewById(R.id.progressBar2);
        productAdapter = new ProductAdapter(this); //adapter object

        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setAdapter(productAdapter);

        loadProducts();
        progressBar2.setVisibility(View.INVISIBLE);


        recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);
                LinearLayoutManager layoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();
                if (!isLoading && layoutManager != null && layoutManager.findLastVisibleItemPosition() == productAdapter.getItemCount() - 1) {
                    skip += limit;


                    progressBar2.setVisibility(View.VISIBLE);


                    Handler handler = new Handler();
                    handler.postDelayed(()->{


                        loadProducts();

                        progressBar2.setVisibility(View.GONE);

                    }, 2000); // 2sec delay

                }



            }
        });


    }

    private void loadProducts() {
        isLoading = true;
        RetrofitClient.getApiService().getProducts(limit, skip).enqueue(new Callback<ProductResponse>() {
            @Override
            public void onResponse(Call<ProductResponse> call, Response<ProductResponse> response) {
                if (response.body() != null) {
                    List<Product> products = response.body().getProducts();
                    productAdapter.addProducts(products);
                }
                isLoading = false;
            }

            @Override
            public void onFailure(Call<ProductResponse> call, Throwable t) {
                isLoading = false;
            }
        });
    }
}

1/  Run the Code And See the Output