How to Create Dynamic Intro Slider in Android using Firebase Firestore?

public class SliderModal {

    // string variable for storing title,
    // image url and description.
    private String title;
    private String heading;
    private String imgUrl;

    public SliderModal() {
        // empty constructor is required
        // when using firebase
    }

    // creating getter methods.
    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getHeading() {
        return heading;
    }

    // creating setter methods
    public void setHeading(String heading) {
        this.heading = heading;
    }

    public String getImgUrl() {
        return imgUrl;
    }

    public void setImgUrl(String imgUrl) {
        this.imgUrl = imgUrl;
    }
    
    // constructor for our modal class
    public SliderModal(String title, String heading, String imgUrl) {
        this.title = title;
        this.heading = heading;
        this.imgUrl = imgUrl;
    }
}

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

import androidx.annotation.NonNull;
import androidx.viewpager.widget.PagerAdapter;

import com.squareup.picasso.Picasso;

import java.util.ArrayList;

public class SliderAdapter extends PagerAdapter {

    // creating variables for layout inflater,
    // context and array list.
    LayoutInflater layoutInflater;
    Context context;
    ArrayList<SliderModal> sliderModalArrayList;

    // creating constructor.
    public SliderAdapter(Context context, ArrayList<SliderModal> sliderModalArrayList) {
        this.context = context;
        this.sliderModalArrayList = sliderModalArrayList;
    }

    @Override
    public int getCount() {
        // inside get count method returning 
        // the size of our array list.
        return sliderModalArrayList.size();
    }
    
    @Override
    public boolean isViewFromObject(@NonNull View view, @NonNull Object object) {
        // inside isViewFromobject method we are 
        // returning our Relative layout object.
        return view == (RelativeLayout) object;
    }

    @NonNull
    @Override
    public Object instantiateItem(@NonNull ViewGroup container, int position) {
        // in this method we will initialize all our layout items
        // and inflate our layout file as well.
        layoutInflater = (LayoutInflater) context.getSystemService(context.LAYOUT_INFLATER_SERVICE);
        
        // below line is use to inflate the layout file which we created.
        View view = layoutInflater.inflate(R.layout.slider_layout, container, false);
        
        // initializing our views.
        ImageView imageView = view.findViewById(R.id.idIV);
        TextView titleTV = view.findViewById(R.id.idTVtitle);
        TextView headingTV = view.findViewById(R.id.idTVheading);

        // setting data to our views.
        SliderModal modal = sliderModalArrayList.get(position);
        titleTV.setText(modal.getTitle());
        headingTV.setText(modal.getHeading());
        Picasso.get().load(modal.getImgUrl()).into(imageView);

        // after setting the data to our views we 
        // are adding the view to our container.
        container.addView(view);
        
        // at last we are returning the view.
        return view;
    }

    @Override
    public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
        // this is a destroy view method which
        // is use to remove a view.
        container.removeView((RelativeLayout) object);
    }
}

import android.os.Bundle;
import android.text.Html;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.viewpager.widget.ViewPager;

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 variables for view pager, 
    // LinearLayout, adapter and our array list.
    private ViewPager viewPager;
    private LinearLayout dotsLL;
    SliderAdapter adapter;
    private ArrayList<SliderModal> sliderModalArrayList;
    private TextView[] dots;
    int size;
    FirebaseFirestore db;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        db = FirebaseFirestore.getInstance();
        
        // initializing all our views.
        viewPager = findViewById(R.id.idViewPager);
        dotsLL = findViewById(R.id.idLLDots);
        
        // in below line we are creating a new array list.
        sliderModalArrayList = new ArrayList<>();
        loadDataFromFirebase();

        // calling method to add dots indicator
        addDots(size, 0);
        
        // below line is use to call on page 
        // change listener method.
        viewPager.addOnPageChangeListener(viewListener);
    }

    private void loadDataFromFirebase() {

        // below line is use to get data from Firebase
        // firestore using collection in android.
        db.collection("SliderData").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.
                                SliderModal sliderModal = d.toObject(SliderModal.class);
                                
                                // after getting data from Firebase we are
                                // storing that data in our array list
                                sliderModalArrayList.add(sliderModal);
                            }
                            // below line is use to add our array list to adapter class.
                            adapter = new SliderAdapter(MainActivity.this, sliderModalArrayList);
                            
                            // below line is use to set our
                            // adapter to our view pager.
                            viewPager.setAdapter(adapter);
                            
                            // we are storing the size of our 
                            // array list in a variable.
                            size = sliderModalArrayList.size();
                        } 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();
            }
        });
    }
    
    private void addDots(int size, int pos) {
        // inside this method we are
        // creating a new text view.
        dots = new TextView[size];
        
        // below line is use to remove all 
        // the views from the linear layout.
        dotsLL.removeAllViews();
        
        // running a for loop to add number
        // of dots to our slider.
        for (int i = 0; i < size; i++) {
            // below line is use to add the dots 
            // and modify its color.
            dots[i] = new TextView(this);
            dots[i].setText(Html.fromHtml("•"));
            dots[i].setTextSize(35);
            
            // below line is called when the
            // dots are not selected.
            dots[i].setTextColor(getResources().getColor(R.color.white));
            dotsLL.addView(dots[i]);
        }
        if (dots.length > 0) {
            // this line is called when the dots 
            // inside linear layout are selected
            dots[pos].setTextColor(getResources().getColor(R.color.purple_200));
        }
    }

    // creating a method for view pager for on page change listener.
    ViewPager.OnPageChangeListener viewListener = new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

        }

        @Override
        public void onPageSelected(int position) {
            // we are calling our dots method to 
            // change the position of selected dots.
            addDots(size, position);
        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    };
}