<!--Permissions for internet-->
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

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

    <!--Grid View for displaying our data from Firebase-->
    <GridView
        android:id="@+id/idGVCourses"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:numColumns="2" />

</RelativeLayout>

public class DataModal {

    // variables for storing our image and name.
    private String name;
    private String imgUrl;

    public DataModal() {
        // empty constructor required for firebase.
    }

    // constructor for our object class.
    public DataModal(String name, String imgUrl) {
        this.name = name;
        this.imgUrl = imgUrl;
    }

    // getter and setter methods
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getImgUrl() {
        return imgUrl;
    }

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

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    android:gravity="center"
    android:orientation="vertical"
    android:padding="4dp">

    <!--Image view for displaying our image-->
    <ImageView
        android:id="@+id/idIVimage"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:layout_margin="4dp"
        android:background="@color/white"
        android:backgroundTint="@color/white"
        android:padding="3dp" />

    <!--Text view for displaying our text -->
    <TextView
        android:id="@+id/idTVtext"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="2dp"
        android:padding="3dp"
        android:text="Category Text"
        android:textAlignment="center"
        android:textColor="@color/black" />

</LinearLayout>

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

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

import com.squareup.picasso.Picasso;

import java.util.ArrayList;

public class CoursesGVAdapter extends ArrayAdapter<DataModal> {

    // constructor for our list view adapter.
    public CoursesGVAdapter(@NonNull Context context, ArrayList<DataModal> dataModalArrayList) {
        super(context, 0, dataModalArrayList);
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {

        // below line is use to inflate the 
        // layout for our item of list view.
        View listitemView = convertView;
        if (listitemView == null) {
            listitemView = LayoutInflater.from(getContext()).inflate(R.layout.image_gv_item, parent, false);
        }

        // after inflating an item of listview item
        // we are getting data from array list inside 
        // our modal class.
        DataModal dataModal = getItem(position);

        // initializing our UI components of list view item.
        TextView nameTV = listitemView.findViewById(R.id.idTVtext);
        ImageView courseIV = listitemView.findViewById(R.id.idIVimage);

        // after initializing our items we are
        // setting data to our view.
        // below line is use to set data to our text view.
        nameTV.setText(dataModal.getName());

        // in below line we are using Picasso to load image
        // from URL in our Image VIew.
        Picasso.get().load(dataModal.getImgUrl()).into(courseIV);

        // below line is use to add item 
        // click listener for our item of list view.
        listitemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // on the item click on our list view.
                // we are displaying a toast message.
                Toast.makeText(getContext(), "Item clicked is : " + dataModal.getName(), Toast.LENGTH_SHORT).show();
            }
        });
        return listitemView;
    }
}

import android.os.Bundle;
import android.widget.GridView;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import com.google.android.gms.tasks.OnFailureListener;
import com.google.android.gms.tasks.OnSuccessListener;
import com.google.firebase.firestore.DocumentSnapshot;
import com.google.firebase.firestore.FirebaseFirestore;
import com.google.firebase.firestore.QuerySnapshot;

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

public class MainActivity extends AppCompatActivity {

    // creating a variable for our 
    // grid view, arraylist and 
    // firebase Firestore.
    GridView coursesGV;
    ArrayList<DataModal> dataModalArrayList;
    FirebaseFirestore db;

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

        // below line is use to initialize our variables.
        coursesGV = findViewById(R.id.idGVCourses);
        dataModalArrayList = new ArrayList<>();

        // initializing our variable for firebase
        // firestore and getting its instance.
        db = FirebaseFirestore.getInstance();

        // here we are calling a method 
        // to load data in our list view.
        loadDatainGridView();
    }

    private void loadDatainGridView() {
        // below line is use to get data from Firebase
        // firestore using collection in android.
        db.collection("Data").get()
                .addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
                    @Override
                    public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
                        // after getting the data we are calling on success method
                        // and inside this method we are checking if the received 
                        // query snapshot is empty or not.
                        if (!queryDocumentSnapshots.isEmpty()) {
                            // if the snapshot is not empty we are hiding our
                            // progress bar and adding our data in a list.
                            List<DocumentSnapshot> list = queryDocumentSnapshots.getDocuments();
                            for (DocumentSnapshot d : list) {

                                // after getting this list we are passing
                                // that list to our object class.
                                DataModal dataModal = d.toObject(DataModal.class);

                                // after getting data from Firebase 
                                // we are storing that data in our array list
                                dataModalArrayList.add(dataModal);
                            }
                            // after that we are passing our array list to our adapter class.
                            CoursesGVAdapter adapter = new CoursesGVAdapter(MainActivity.this, dataModalArrayList);

                            // after passing this array list 
                            // to our adapter class we are setting 
                            // our adapter to our list view.
                            coursesGV.setAdapter(adapter);
                        } else {
                            // if the snapshot is empty we are displaying a toast message.
                            Toast.makeText(MainActivity.this, "No data found in Database", Toast.LENGTH_SHORT).show();
                        }
                    }
                }).addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                // we are displaying a toast message 
                // when we get any error from Firebase.
                Toast.makeText(MainActivity.this, "Fail to load data..", Toast.LENGTH_SHORT).show();
            }
        });
    }
}