GridView con imagenes en miniatura

<GridView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/GridView1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:gravity="center"
    android:horizontalSpacing="10dp"
    android:numColumns="3"
    android:stretchMode="columnWidth"
    android:verticalSpacing="10dp"
    tools:context=".GridImageActivity" >

</GridView>

package com.bolivia.samplegallery;

import java.util.ArrayList;
import android.content.Context;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;

public class GridViewImageAdapter extends BaseAdapter {

 private Context mContext;
 private ArrayList<Integer> listPhoto = new ArrayList<Integer>(); 

 /** Constructor de clase */
 public GridViewImageAdapter(Context c){
  mContext = c;
  //se cargan las miniaturas
  listPhoto.add(R.drawable.foto1);
  listPhoto.add(R.drawable.foto2);
  listPhoto.add(R.drawable.foto3);
  listPhoto.add(R.drawable.foto4);
  listPhoto.add(R.drawable.foto5);
  listPhoto.add(R.drawable.foto6);
  listPhoto.add(R.drawable.foto7);
  listPhoto.add(R.drawable.foto8);
  listPhoto.add(R.drawable.foto9);
 }

 @Override
 public int getCount() {
  return listPhoto.size();
 }

 @Override
 public Object getItem(int position) {
  return listPhoto.get(position);
 }

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

 @Override
 public View getView(int position, View view, ViewGroup viewgroup) {
  ImageView imageView = new ImageView(mContext);
  imageView.setImageResource( listPhoto.get(position) );
  imageView.setScaleType( ImageView.ScaleType.CENTER_CROP );
  imageView.setLayoutParams( new GridView.LayoutParams(180, 220) );
  return imageView;  
 }

}

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_grid_image);
  //---------->Nuevo codigo
  GridView gridView = (GridView) findViewById( R.id.GridView1 );
  gridView.setAdapter( new GridViewImageAdapter(this) );
  //---------->fin
 }