Is there any LazyLoader for images to load image in ListField in BlackBerry?

Question

I am new to BlackBerry development. But good about android.

I want to load Images coming from the server in ListField.

I have implement like below code but not getting success:

   package mypackage;


public class TempScreen extends MainScreen implements ListFieldCallback{
    Bitmap[] images=null;
    private ListField mylist;
    private static Bitmap _bitmap;
    private ImageDownloader downloader;
    int size = 0;
    String[] urls={
            "http://www.kentnews.co.uk/polopoly_fs/damian_lewis_at_port_lympne_wild_animal_park_c_taf_1_1738362!image/2626063106.jpg_gen/derivatives/landscape_225/2626063106.jpg",
            "http://www.kentnews.co.uk/polopoly_fs/damian_lewis_at_port_lympne_wild_animal_park_c_taf_1_1738362!image/2626063106.jpg_gen/derivatives/landscape_225/2626063106.jpg",
            "http://www.kentnews.co.uk/polopoly_fs/damian_lewis_at_port_lympne_wild_animal_park_c_taf_1_1738362!image/2626063106.jpg_gen/derivatives/landscape_225/2626063106.jpg",
            "http://www.kentnews.co.uk/polopoly_fs/damian_lewis_at_port_lympne_wild_animal_park_c_taf_1_1738362!image/2626063106.jpg_gen/derivatives/landscape_225/2626063106.jpg"};
    public TempScreen()
    {


        images=new Bitmap[urls.length];
        size = urls.length;
        mylist = new ListField();
        mylist.setCallback(this);
        mylist.setSize(4);
        mylist.setRowHeight(getFont().getHeight() * 3);
        add(mylist);
        Thread downloader=new Thread(new ImageDownloader());
        downloader.start();

    }


    public void drawListRow(ListField listField, Graphics graphics, int index,
            int y, int width) {

        if(images[index]==null)
         {
             //Load placeholder image
            _bitmap = Bitmap.getBitmapResource("close_btn.png");// load some bitmap
            // of your choice
            // here
         }
         else
             //Load Bitmap
            _bitmap = images[index]; 

        graphics.drawText("row details", 100, y + 30);
        //graphics.drawBitmap(0, y, _bitmap.getWidth(), _bitmap.getHeight(),_bitmap, 0, 0);
        mylist.invalidate(index);
    }

    public class ImageDownloader implements Runnable
    {
        public void run()
        { 
            for(int i=0; i<size;i++)
            { 
                 if(images[i]==null) 
                 { 
                      images[i]=connectServerForImage(urls[i].toString());//replace downloadImage method to whatever method       you have to download the bitmap from url 
                      UiApplication.getUiApplication().invokeLater(new Runnable(){
                          public void run()
                          {
                              mylist.invalidate();
                          }
                      });
                  }
             }
        }
    }
    public Object get(ListField listField, int index) {
        // TODO Auto-generated method stub
        return null;
    }
    public int getPreferredWidth(ListField listField) {
        // TODO Auto-generated method stub
        return 0;
    }
    public int indexOfList(ListField listField, String prefix, int start) {
        // TODO Auto-generated method stub
        return 0;
    }
    public static Bitmap connectServerForImage(String url) {
        HttpConnection httpConnection = null;
        DataOutputStream httpDataOutput = null;
        InputStream httpInput = null;
        int rc;
        Bitmap bitmp = null;
        try {
            // httpConnection = (HttpConnection)
            // Connector.open(url+";interface=wifi");
            httpConnection = (HttpConnection) Connector.open(url);
            rc = httpConnection.getResponseCode();
            // System.out.println("===============================");
            Dialog.alert("beore if condition");
            if (rc == HttpConnection.HTTP_OK) {

                System.out.println(" ============= IN FUNCTION. . . . .");
                httpInput = httpConnection.openInputStream();
                InputStream inp = httpInput;
                byte[] b = IOUtilities.streamToBytes(inp);
                EncodedImage hai = EncodedImage.createEncodedImage(b, 0,
                        b.length);
                bitmp = hai.getBitmap();
            } else {
                throw new IOException("HTTP response code: " + rc);
            }
        } catch (Exception ex) {
            System.out.println("URL Bitmap Error........" + ex.getMessage());
        } finally {
            try {
                if (httpInput != null)
                    httpInput.close();
                if (httpDataOutput != null)
                    httpDataOutput.close();
                if (httpConnection != null)
                    httpConnection.close();

            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return bitmp;
    }
}

Dont know where i am wrong. Please can any budy help me for the same.

Answer 1

You can try using this link : http://www.coderholic.com/blackberry-webbitmapfield/

You have to create a separate class named as WebBitmapField as suggested in above link.

How to use that class in your list field image objects:

• For every image url create WebBitmapField object

• photoList_vector is the vector through which populate elements in list field

  WebBitmapField web = new WebBitmapField("http://www.image1.png"); 
  
  photoList_vector.addElement(web);
  
  web = new WebBitmapField("http://www.image2.png"); 
  
  photoList_vector.addElement(web);
  

Now use this vector to work on your list field......

In the above lines we try to ensure that when we simultaneously send multiple requests to get the images then each image corresponds to a particular WebBitmapField Object.

Each object is then added to vector so that it can be added to the list field.

Each url send is tied to an object of WebBitmapField.

So though request is send in a separate thread it gets tied to its associated object only

Hope it helps :)