Android : สอบถามเรื่องการแสดงภาพจากภาพเล็กเป็นภาพใหญ่เมื่อกด

public class MainActivity extends AppCompatActivity {
//    public Activity activity;
//    public int[] array = {R.drawable.pic_a, R.drawable.pic_b,
//            R.drawable.pic_c, R.drawable.pic_d,
//            R.drawable.pic_e, R.drawable.pic_f,
//            R.drawable.pic_g, R.drawable.pic_h,
//            R.drawable.pic_i
//    };

//    public MainActivity(Activity activity) {
//        this.activity = activity;
//    }

    @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 AdapterView.OnItemClickListener() {
            public void onItemClick(AdapterView<?> parent, View v,
                                    int position, long id) {
                Toast.makeText(MainActivity.this, "" + position,
                        Toast.LENGTH_SHORT).show();

                AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
                ImageView imageView = new ImageView(MainActivity.this);
                //imageView.setImageResource(R.mipmap.pic_a);
                imageView.setAdjustViewBounds(true);
                builder.setView(imageView);
                builder.show();
            }
        });
    }
}

public class ImageAdapter extends BaseAdapter {
    private Context mContext;

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

    public int getCount() {
        return mThumbIds.length;
    }

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

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

    public View getView(int position, View convertView, ViewGroup parent) {
        ImageView imageView;
        if (convertView == null) {
            imageView = new ImageView(mContext);
            //imageView.setLayoutParams(new ViewGroup.LayoutParams(200, 200));
            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
            imageView.setAdjustViewBounds(true);
        } else {
            imageView = (ImageView) convertView;
        }

        imageView.setImageResource(mThumbIds[position]);
        return imageView;
    }

    private Integer[] mThumbIds = {
            R.mipmap.pic_a, R.mipmap.pic_b,
            R.mipmap.pic_c, R.mipmap.pic_d,
            R.mipmap.pic_e, R.mipmap.pic_f,
            R.mipmap.pic_g, R.mipmap.pic_h,
            R.mipmap.pic_i,};
}