Android using GridView with OnScrollListener

I am creating a gridview that contains many images, probably about 1000 ++ images. To reduce load time for gridview, I want to implement onScrollListener using AbsListView. I will limit 20 images to viewing, then when the scroll reaches the bottom, it will load another 20 images. This will be repeated until all images have been downloaded.

I was a Google search pattern, but didn't seem to find one that matches my codes. Can someone guide me how this is done? I am currently using imageloader Lazylist for my images. I also use AsyncTask.

MainGridView.class

    public class MainGridView extends SherlockActivity {

    private ProgressDialog pDialog;
    ArrayList<HashMap<String, String>> songsList;
    static final String KEY_SONG = "song"; 
    static final String KEY_ID = "id";
    static final String KEY_TITLE = "title";
    static final String KEY_ARTIST = "artist";
    static final String KEY_CAT_ARTIST = "artistcat";
    static final String KEY_DURATION = "duration";
    static final String KEY_THUMB_URL = "thumb_url";
    static final String KEY_BIG_URL = "big_url";
    static final String KEY_CAT_URL = "cat_url";
    static String IMAGE_POSITION;
    GridView grid;
    MainGridViewLazyAdapter adapter;
    String cat_url;
    String artist_url;
    private int visibleThreshold = 5;
    private int currentPage = 0;
    private int previousTotal = 0;
    private boolean loading = true;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.gridview_main);

        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        checkInternetConnection();

        grid = (GridView) findViewById(R.id.grid_view);




    grid.setOnScrollListener(new OnScrollListener() {

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem,
            int visibleItemCount, int totalItemCount) {
        // TODO Auto-generated method stub
        if (loading) {
            if (visibleItemCount > totalItemCount) {
                loading = false;
                previousTotal = totalItemCount;
                currentPage++;
            }
        }
        if (!loading && (totalItemCount - visibleItemCount) <= (firstVisibleItem + visibleThreshold)) {
            // I load the next page of gigs using a background task,
            // but you can call any function here.
            new loadGridView().execute(currentPage + 1);
            loading = true;
        }
    }

    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        // TODO Auto-generated method stub

    }
    });


}

    public class loadGridView extends AsyncTask<Integer, String, String> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(MainGridView.this);
            pDialog.setTitle("Connect to Server");
            pDialog.setMessage("This process can take a few seconds to a few minutes, depending on your Internet Connection Speed.");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(false);
            pDialog.show();
        }
        @Override
        protected String doInBackground(Integer... args) {
            // updating UI from Background Thread
                    Intent in = getIntent();
                    songsList = new ArrayList<HashMap<String, String>>();
                    cat_url = in.getStringExtra(KEY_CAT_URL);
                    artist_url = in.getStringExtra(KEY_CAT_ARTIST);


                    XMLParser parser = new XMLParser();
                    String xml = parser.getXmlFromUrl(cat_url); // getting XML from URL
                    Document doc = parser.getDomElement(xml); // getting DOM element

                    NodeList nl = doc.getElementsByTagName(KEY_SONG);
                    // looping through all song nodes <song>
                    for (int i = 0; i < nl.getLength(); i++) {
                        // creating new HashMap
                        HashMap<String, String> map = new HashMap<String, String>();
                        Element e = (Element) nl.item(i);
                        // adding each child node to HashMap key => value
                        map.put(KEY_ID, parser.getValue(e, KEY_ID));
                        map.put(KEY_TITLE, parser.getValue(e, KEY_TITLE));
                        map.put(KEY_ARTIST, parser.getValue(e, KEY_ARTIST));
                        map.put(KEY_DURATION, parser.getValue(e, KEY_DURATION));
                        map.put(KEY_THUMB_URL, parser.getValue(e, KEY_THUMB_URL));
                        map.put(KEY_BIG_URL, parser.getValue(e, KEY_BIG_URL));
                        // adding HashList to ArrayList
                        songsList.add(map);

                    }
                    return null;
                }   


        @Override
        protected void onPostExecute(String args) {
            ActionBar   ab = getSupportActionBar();
                        ab.setTitle(artist_url);

            adapter=new MainGridViewLazyAdapter(MainGridView.this, songsList);   
            grid.setAdapter(adapter);
            pDialog.dismiss();
            }
        }