ListField display image from URL

I am displaying a customized list field with text on the right side and image on the left side.The image comes from a URL dynamically. Initially i am placing a blank image on the left of the list field,then call URLBitmapField class's setURL method,which actually does the processing and places the processed image on top of the blank image.The image gets displayed on the list field,but to see that processed image i need to click on the list field image.I want the processed image to be displayed automatically in the list field after the processing.Can anyone tell me where i am getting wrong?I have been asking for help,but no one seems to figure out the problem.Any productive suggestions would be appreciated

import java.util.Vector;
import net.rim.device.api.system.Bitmap;
import net.rim.device.api.system.Display;
import net.rim.device.api.ui.ContextMenu;
import net.rim.device.api.ui.DrawStyle;
import net.rim.device.api.ui.Field;
import net.rim.device.api.ui.Font;
import net.rim.device.api.ui.Graphics;
import net.rim.device.api.ui.Manager;
import net.rim.device.api.ui.MenuItem;
import net.rim.device.api.ui.UiApplication;
import net.rim.device.api.ui.component.BitmapField;
import net.rim.device.api.ui.component.Dialog;
import net.rim.device.api.ui.component.LabelField;
import net.rim.device.api.ui.component.ListField;
import net.rim.device.api.ui.component.ListFieldCallback;
import net.rim.device.api.ui.component.NullField;
import net.rim.device.api.ui.container.FullScreen;
import net.rim.device.api.ui.container.MainScreen;
import net.rim.device.api.ui.container.VerticalFieldManager;
import net.rim.device.api.util.Arrays;
import net.rim.device.api.ui.component.ListField;

public class开发者_如何学Go TaskListField extends UiApplication {
    // statics
    // ------------------------------------------------------------------
    public static void main(String[] args) {
        TaskListField theApp = new TaskListField();
        theApp.enterEventDispatcher();
    }

    public TaskListField() {
        pushScreen(new TaskList());
    }

}

class TaskList extends MainScreen implements ListFieldCallback {
    private Vector rows;
    private Bitmap p1;
    private Bitmap p2;
    private Bitmap p3;
    String Task;
    ListField listnew = new ListField();
    private VerticalFieldManager metadataVFM;
    TableRowManager row;



    public TaskList() {
        super();
        URLBitmapField artistImgField;
        listnew.setRowHeight(80);
        listnew.setCallback(this);
        rows = new Vector();
        for (int x = 0; x <3; x++) {

               row = new TableRowManager();

            artistImgField = new URLBitmapField(Bitmap
                    .getBitmapResource("res/images/bg.jpg"));

            row.add(artistImgField);

            String photoURL = "someimagefrmurl.jpg";
            Log.info(photoURL);

            // strip white spaces in the url, which is causing the
            // images to not display properly
            for (int i = 0; i < photoURL.length(); i++) {
                if (photoURL.charAt(i) == ' ') {
                    photoURL = photoURL.substring(0, i) + "%20"
                            + photoURL.substring(i + 1,    photoURL.length());
                }
            }
            Log.info("Processed URL: " + photoURL);
            artistImgField.setURL(photoURL);



            LabelField task = new LabelField("Display");

            row.add(task);

            LabelField task1 = new LabelField(
                    "Now Playing" + String.valueOf(x));


            Font myFont = Font.getDefault().derive(Font.PLAIN, 12);
            task1.setFont(myFont);

            row.add(task1);


            rows.addElement(row);
        }
        listnew.setSize(rows.size());


        this.add(listnew);
         //listnew.invalidate();
    }

    // ListFieldCallback Implementation
    public void drawListRow(ListField listField, Graphics g, int index, int y,
            int width) {
        TableRowManager rowManager = (TableRowManager) rows.elementAt(index);

        rowManager.drawRow(g, 0, y, width, listnew.getRowHeight());
    }
    protected void drawFocus(Graphics graphics, boolean on) {
    }



    private class TableRowManager extends Manager {
        public TableRowManager() {
            super(0);

        }

        // Causes the fields within this row manager to be layed out then
        // painted.
        public void drawRow(Graphics g, int x, int y, int width, int height) {
            // Arrange the cell fields within this row manager.
            layout(width, height);

            // Place this row manager within its enclosing list.
            setPosition(x, y);

            // Apply a translating/clipping transformation to the graphics
            // context so that this row paints in the right area.
            g.pushRegion(getExtent());

            // Paint this manager's controlled fields.
            subpaint(g);

            g.setColor(0x00CACACA);
            g.drawLine(0, 0, getPreferredWidth(), 0);

            // Restore the graphics context.
            g.popContext();

        }

        // Arrages this manager's controlled fields from left to right within
        // the enclosing table's columns.
        protected void sublayout(int width, int height) {
            // set the size and position of each field.
            int fontHeight = Font.getDefault().getHeight();
            int preferredWidth = getPreferredWidth();

            // start with the Bitmap Field of the priority icon
            Field field = getField(0);
            layoutChild(field, 146,80);
            setPositionChild(field, 0, 0);

            // set the task name label field
            field = getField(1);
            layoutChild(field, preferredWidth - 16, fontHeight + 1);
            setPositionChild(field, 149, 3);

            // set the list name label field
            field = getField(2);
            layoutChild(field, 150, fontHeight + 1);
            setPositionChild(field, 149, fontHeight + 6);


            setExtent(360, 480);

        }

        // The preferred width of a row is defined by the list renderer.
        public int getPreferredWidth() {
            return listnew.getWidth();
        }

        // The preferred height of a row is the "row height" as defined in the
        // enclosing list.
        public int getPreferredHeight() {
            return listnew.getRowHeight();
        }
    }

    public Object get(ListField listField, int index) {
        // TODO Auto-generated method stub
        return null;
    }

    public int getPreferredWidth(ListField listField) {

    return 0;
    }

    public int indexOfList(ListField listField, String prefix, int start) {
        // TODO Auto-generated method stub
        return 0;
    }

}

Finally i solved it of my own. This worked:

UiApplication.getUiApplication().invokeLater(
    new Runnable() {
        public void run() {
            listnew.invalidate();
        }
    },500,true);