Retrive image in Firebase Database using GridView in Android Studio Java

ImageRetrieve.java

package com.example.learningfirebase;

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

import android.content.Context;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.Toast;

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 com.squareup.picasso.Picasso;

import java.util.ArrayList;
import java.util.List;

public class ImageRetrieve extends AppCompatActivity {

    DatabaseReference databaseReference;
    GridView gridView;
    ArrayList<Upload> list;
    CustomAdapter customAdapter;

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

        databaseReference = FirebaseDatabase.getInstance().getReference("Images"); /**Inniciate databaseReferance eka*/
        gridView = (GridView) findViewById(R.id.grdv1);
        list = new ArrayList<>(); /**Array list eke data type eka wenne Upload Class eka... eeka nisa access karaddid ehenmama wenna oone*/

        customAdapter = new CustomAdapter(this,list);
        gridView.setAdapter(customAdapter);

        databaseReference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                for (DataSnapshot dataSnapshot1 : dataSnapshot.getChildren()){
                    System.out.println(dataSnapshot1);
                    Upload upload = dataSnapshot1.getValue(Upload.class); /**dataSnapshot1 eken ganna value class ekakataa add karanawa eewa access karanna pahasu wemma*/
                    list.add(upload); /**Object eka list ekata add karanawa*/
                }
                /*Awasaanayedi list ekata object okkoma assign wela*/
                customAdapter.notifyDataSetChanged(); // Api Custome adapter eka notify karanawa
            }
            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                Toast.makeText(ImageRetrieve.this, databaseError.getMessage(), Toast.LENGTH_SHORT).show();
            }
        });
    }
}
class CustomAdapter extends BaseAdapter{
    Context context;
    ArrayList<Upload> list;
    LayoutInflater layoutInflater;

    public CustomAdapter(Context context, ArrayList<Upload> list) {
        this.context = context;
        this.list = list;
        layoutInflater = LayoutInflater.from(context);
    }

    @Override
    public int getCount() {
        return list.size();
    }

    @Override
    public Object getItem(int position) {
        return null;
    }

    @Override
    public long getItemId(int position) {
        return 0;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        convertView = layoutInflater.inflate(R.layout.item_view,null);
        ImageView imageView = (ImageView) convertView.findViewById(R.id.imageItem);

        Upload currentUpload = list.get(position);/**methandi List eke current item eka Upload class ekata set wenawa*/
        Picasso.get().
                load(currentUpload.getImgUrl()). /** E Set una current item eke getImgUrl() method ekata cl karala return karagannawa image eke url eka */
                into(imageView); /**set wenawa imageView ekata*/
        return convertView;
    }
}
class Upload{
    private String imgUrl;

    public Upload() {
    }

    public Upload(String imgUrl) {
        this.imgUrl = imgUrl;
    }

    public String getImgUrl() {
        return imgUrl;
    }

    public void setImgUrl(String imgUrl) {
        this.imgUrl = imgUrl;
    }
}