gridview with square cells, look at setupAdapter()

gallery_item.xml

<?xml version="1.0" encoding="utf-8"?>
<ImageView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/gallery_item_imageView"
    android:layout_width="match_parent"
    android:layout_height="120dp"
    android:layout_gravity="center"
    android:contentDescription="@string/grid_image_description"
    android:scaleType="centerCrop" />

PhotoGalleryFragment.java

package com.rdm.photogallery;

import java.util.ArrayList;

import android.app.Activity;
import android.app.Fragment;
import android.app.SearchManager;
import android.app.SearchableInfo;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.graphics.Bitmap;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Build;
import android.os.Bundle;
import android.os.Handler;
import android.preference.PreferenceManager;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.SearchView;

import com.rdm.photogallery.ThumbnailDownloader.Listener;

public class PhotoGalleryFragment extends Fragment {
    private static final String TAG = "PhotoGalleryFragment";

    private GridView mGridView;
    private ArrayList<GalleryItem> mItems;
    private int mCurrentPage = 0;
    private int mFetchedPage = 0;
    private ThumbnailDownloader<ImageView> mThumbnailThread;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setRetainInstance(true);
        setHasOptionsMenu(true);

        updateItems();

        mThumbnailThread = new ThumbnailDownloader<ImageView>(new Handler());
        mThumbnailThread.setListener(new Listener<ImageView>() {
            @Override
            public void onThumbnailDownloaded(ImageView imageView, Bitmap thumbnail) {
                if (isVisible()) {
                    imageView.setImageBitmap(thumbnail);
                }
            }
        });
        mThumbnailThread.start();
        mThumbnailThread.getLooper();
        Log.i(TAG, "Background thread started");
    }

    public void reset() {
        mCurrentPage = 0;
        mFetchedPage = 0;
        mItems.clear();
    }

    public void updateItems() {
        new FetchItemsTask().execute(++mCurrentPage);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_photo_gallery, container, false);
        mItems = new ArrayList<GalleryItem>();

        mGridView = (GridView)v.findViewById(R.id.gridView);
        mGridView.setOnItemClickListener(new OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> gridView, View view,
                    int pos, long id) {
                GalleryItem item = mItems.get(pos);

                Uri photoPageUri = Uri.parse(item.getPhotoUrl());
                Intent i = new Intent(getActivity(), PhotoPageActivity.class);
                i.setData(photoPageUri);

                startActivity(i);
            }
        });
        mGridView.setOnScrollListener(new OnScrollListener() {
            int lastFirstVisibleItem = -1;

            @Override
            public void onScrollStateChanged(AbsListView view, int scrollState) {
            }

            @Override
            public void onScroll(AbsListView view, int firstVisibleItem,
                    int visibleItemCount, int totalItemCount) {
                if (visibleItemCount > 0 &&
                        firstVisibleItem + visibleItemCount == totalItemCount &&
                        mCurrentPage == mFetchedPage) {
                    updateItems();
                    Log.i(TAG, "Scrolled to end of " + totalItemCount +", fetching next page, #" + mCurrentPage);
                }

                // The adapter or view code is calling this routine after each image in the
                // grid is filled. Let's just call it once per scrolled position.
                if (firstVisibleItem == lastFirstVisibleItem || totalItemCount == 0)
                    return;
                lastFirstVisibleItem = firstVisibleItem;

                int start = firstVisibleItem + visibleItemCount;
                int end = start + 30 > mItems.size() ? mItems.size() : start + 30;
                //                int start2 = firstVisibleItem - 1;
                //                int end2 = start2 - 30 < 1 ? 1 : start2 - 30;
                //
                //                Log.i(TAG, "Prefetch: (" + start + ", " + end + ") + (" + start2 + ", " + end2 + ")");

                for (int i = start; i < end; i++) {
                    mThumbnailThread.queueThumbnail(null, mItems.get(i).getUrl());
                }
                start = firstVisibleItem - 1;
                end = start - 30 < 1 ? 1 : start - 30;
                for (int i = start; i > end; i--) {
                    mThumbnailThread.queueThumbnail(null, mItems.get(i).getUrl());
                }
            }
        });

        setupAdapter();

        return v;
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        mThumbnailThread.quit();
        Log.i(TAG, "Background thread destroyed");
    }

    @Override
    public void onDestroyView() {
        super.onDestroyView();
        mThumbnailThread.clearQueue();
    }

    private void setupSearchView(Menu menu) {
        // Pull out the SearchView
        MenuItem searchItem = menu.findItem(R.id.menu_item_search);
        SearchView searchView = (SearchView)searchItem.getActionView();

        // Get the data from our searchable.xml as a SearchableInfo
        SearchManager searchManager = (SearchManager)getActivity()
                .getSystemService(Context.SEARCH_SERVICE);
        ComponentName name = getActivity().getComponentName();
        SearchableInfo searchInfo = searchManager.getSearchableInfo(name);

        searchView.setSearchableInfo(searchInfo);
    }

    @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        super.onCreateOptionsMenu(menu, inflater);
        inflater.inflate(R.menu.fragment_photo_gallery, menu);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
            setupSearchView(menu);
        }
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        case R.id.menu_item_search:
            getActivity().onSearchRequested();
            return true;
        case R.id.menu_item_clear:
            PreferenceManager.getDefaultSharedPreferences(getActivity())
            .edit()
            .putString(FlickrFetchr.PREF_SEARCH_QUERY, null)
            .commit();
            reset();
            updateItems();
            return true;
        case R.id.menu_item_toggle_polling:
            boolean shouldStartAlarm = !PollService.isServiceAlarmOn(getActivity());
            PollService.setServiceAlarm(getActivity(), shouldStartAlarm);

            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
                getActivity().invalidateOptionsMenu();
            }

            return true;
        default:
            return super.onOptionsItemSelected(item);
        }
    }

    @Override
    public void onPrepareOptionsMenu(Menu menu) {
        super.onPrepareOptionsMenu(menu);

        MenuItem toggleItem = menu.findItem(R.id.menu_item_toggle_polling);
        if (PollService.isServiceAlarmOn(getActivity())) {
            toggleItem.setTitle(R.string.stop_polling);
        } else {
            toggleItem.setTitle(R.string.start_polling);
        }
    }

    void setupAdapter() {
        if (getActivity() == null || mGridView == null) return;

        if (mGridView.getAdapter() == null) {
            mGridView.setAdapter(new GalleryItemAdapter(mItems));
        } else {
            GalleryItemAdapter adapter = (GalleryItemAdapter)mGridView.getAdapter();
            adapter.notifyDataSetChanged();
        }
    }

    private class FetchItemsTask extends AsyncTask<Integer,Void,ArrayList<GalleryItem>> {
        @Override
        protected ArrayList<GalleryItem> doInBackground(Integer... params) {
            Activity activity = getActivity();
            if (activity == null)
                return new ArrayList<GalleryItem>();

            String query = PreferenceManager.getDefaultSharedPreferences(activity)
                    .getString(FlickrFetchr.PREF_SEARCH_QUERY, null);
            if (query != null)
                return new FlickrFetchr().search(query, params[0]);

            return new FlickrFetchr().fetchItems(params[0]);
        }

        @Override
        protected void onPostExecute(ArrayList<GalleryItem> items) {
            Log.i(TAG, "Items returned = " + items.size());
            mItems.addAll(items);
            mFetchedPage++;
            setupAdapter();
        }
    }

    private class GalleryItemAdapter extends ArrayAdapter<GalleryItem> {
        public GalleryItemAdapter(ArrayList<GalleryItem> items) {
            super(getActivity(), 0, items);
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            if (convertView == null) {
                convertView = getActivity().getLayoutInflater()
                        .inflate(R.layout.gallery_item, parent, false);
            }

            ImageView imageView = (ImageView)convertView.findViewById(R.id.gallery_item_imageView);
            imageView.setImageDrawable(null);
            //imageView.setImageResource(R.drawable.brian_up_close);
            GalleryItem item = getItem(position);
            mThumbnailThread.queueThumbnail(imageView, item.getUrl());

            return convertView;
        }

    }

}