Eu estou construindo um gridview que contém muitas imagens provavelmente em torno de 1000 imagens ++. Para reduzir o tempo de carregamento para o gridview, eu quero implementar um onScrollListener usando AbsListView. Vou limitar 20 imagens por visualização e, quando a rolagem chegar ao fundo, irá carregar outras 20 imagens. Isso será repetido até que todas as imagens tenham sido carregadas.

Eu tenho googling amostras, mas parece não encontrar um que se adapte aos meus códigos. Alguém poderia me orientar como é feito? Atualmente estou usando o imagyloader Lazylist para minhas imagens. Também estou usando o 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();
            }
        }