package com.example.galleryview;

import android.os.Bundle;
import android.widget.Gallery;
import android.widget.ImageView;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    Gallery simpleGallery;

    // CustomizedGalleryAdapter is a java/kotlin
    // class which extends BaseAdapter
    // and implement the override methods.
    CustomizedGalleryAdapter customGalleryAdapter;
    ImageView selectedImageView;

    // To show the selected language, we need this
    // array of images, here taken 10 different kind of
    // most popular programming languages
    int[] images = {
            R.drawable.circle,
            R.drawable.dice,
            R.drawable.genie,
            R.drawable.pumpkin,
            R.drawable.rocket,
            R.drawable.circle,
            R.drawable.dice,
            R.drawable.genie,
            R.drawable.pumpkin,
            R.drawable.rocket
    };

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

        // Our layout is activity_main
        // get the reference of Gallery. As we are showing
        // languages it is named as languagesGallery
        // meaningful names will be good for easier understanding
        simpleGallery = (Gallery) findViewById(R.id.languagesGallery);

        // get the reference of ImageView
        selectedImageView = (ImageView) findViewById(R.id.imageView);

        // initialize the adapter
        customGalleryAdapter = new CustomizedGalleryAdapter(getApplicationContext(), images);

        // set the adapter for gallery
        simpleGallery.setAdapter(customGalleryAdapter);

        // Let us do item click of gallery and image can be identified by its position
        simpleGallery.setOnItemClickListener((parent, view, position, id) -> {
            // Whichever image is clicked, that is set in the selectedImageView
            // position will indicate the location of image
            selectedImageView.setImageResource(images[position]);
        });
    }
}

package com.example.galleryview;

import android.content.Context;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Gallery;
import android.widget.ImageView;

public class CustomizedGalleryAdapter extends BaseAdapter {

    private final Context context;
    private final int[] images;

    public CustomizedGalleryAdapter(Context c, int[] images) {
        context = c;
        this.images = images;
    }

    // returns the number of images, in our example it is 10
    public int getCount() {
        return images.length;
    }

    // returns the Item of an item, i.e. for our example we can get the image
    public Object getItem(int position) {
        return position;
    }

    // returns the ID of an item
    public long getItemId(int position) {
        return position;
    }

    // returns an ImageView view
    public View getView(int position, View convertView, ViewGroup parent) {
        // position argument will indicate the location of image
        // create a ImageView programmatically
        ImageView imageView = new ImageView(context);

        // set image in ImageView
        imageView.setImageResource(images[position]);

        // set ImageView param
        imageView.setLayoutParams(new Gallery.LayoutParams(200, 200));
        return imageView;
    }
}