What is GridView

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

<GridView
    android:id="@+id/gridview"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
      android:numColumns="auto_fit"
      android:verticalSpacing="10dp"
      android:horizontalSpacing="10dp"
      android:columnWidth="90dp"
      android:stretchMode="columnWidth"
      android:gravity="center" />

</LinearLayout>

package com.java2s.myapplication3.app;
/*from   w  w  w.ja  v a2  s  .  com*/
import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.Toast;

public class MainActivity extends Activity {
    //the images to display
    Integer[] imageIDs = {
            R.drawable.ic_launcher,
            R.drawable.ic_launcher,
            R.drawable.ic_launcher,
            R.drawable.ic_launcher,
            R.drawable.ic_launcher,
            R.drawable.ic_launcher,
            R.drawable.ic_launcher
    };
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        GridView gridView = (GridView) findViewById(R.id.gridview);
        gridView.setAdapter(new ImageAdapter(this));

        gridView.setOnItemClickListener(new OnItemClickListener()
        {
            public void onItemClick(AdapterView parent,
                                    View v, int position, long id)
            {
                Toast.makeText (getBaseContext(),
                        "pic" + (position + 1) + " selected",
                        Toast.LENGTH_SHORT).show();
            }
        });

    }

    public class ImageAdapter extends BaseAdapter
    {
        private Context context;

        public ImageAdapter(Context c)
        {
            context = c;
        }

        //returns the number of images
        public int getCount() {
            return imageIDs.length;
        }

        //returns the item
        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)
        {
            ImageView imageView;
            if (convertView == null) {
                imageView = new ImageView(context);
                imageView.setLayoutParams(new
                        GridView.LayoutParams(85, 85));
                imageView.setScaleType(
                        ImageView.ScaleType.CENTER_CROP);
                imageView.setPadding(5, 5, 5, 5);
            } else {
                imageView = (ImageView) convertView;
            }
            imageView.setImageResource(imageIDs[position]);
            return imageView;
        }
    }

}