Java 从url显示图像的自定义列表字段

我正在显示一个自定义列表字段，右侧为文本，左侧为图像。图像动态地来自URL。最初，我在列表字段左侧放置一个空白图像，然后调用URLBitmapField类的setURL方法，它实际处理并将处理后的图像放在空白图像的顶部。图像显示在列表字段上，但要查看处理后的图像，我需要按任意键或单击列表字段项。我希望处理后的图像在列表字段中自动显示。有人能告诉我哪里出错了吗

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 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;
    }

}

import java.util.Vector；
导入net.rim.device.api.system.Bitmap；
导入net.rim.device.api.system.Display；
导入net.rim.device.api.ui.ContextMenu；
导入net.rim.device.api.ui.DrawStyle；
导入net.rim.device.api.ui.Field；
导入net.rim.device.api.ui.Font；
导入net.rim.device.api.ui.Graphics；
导入net.rim.device.api.ui.Manager；
导入net.rim.device.api.ui.MenuItem；
导入net.rim.device.api.ui.ui应用程序；
导入net.rim.device.api.ui.component.BitmapField；
导入net.rim.device.api.ui.component.Dialog；
导入net.rim.device.api.ui.component.LabelField；
导入net.rim.device.api.ui.component.ListField；
导入net.rim.device.api.ui.component.ListFieldCallback；
导入net.rim.device.api.ui.component.NullField；
导入net.rim.device.api.ui.container.FullScreen；
导入net.rim.device.api.ui.container.main屏幕；
导入net.rim.device.api.ui.container.VerticalFieldManager；
导入net.rim.device.api.util.array；
导入net.rim.device.api.ui.component.ListField；
公共类TaskListField扩展了UiApplication{
//静力学
// ------------------------------------------------------------------
公共静态void main（字符串[]args）{
TaskListField theApp=新建TaskListField（）；
theApp.enterEventDispatcher（）；
}
公共任务列表字段（）{
推屏（新任务列表（））；
}
}
类TaskList扩展MainScreen实现ListFieldCallback{
专用向量行；
私有位图p1；
私有位图p2；
私有位图p3；
字符串任务；
ListField listnew=新ListField（）；
私有VerticalFieldManager元数据vfm；
TableRowManager行；
公共任务列表（）{
超级（）；
URLBitmapField ArtistingField；
listnew.setRowHeight（80）；
setCallback（this）；
行=新向量（）；
对于（int x=0；x尝试调用字段的validate（）方法。
我在要添加它的管理器上调用了invalidate方法，即rowmanager.invalidate（）.但这并没有什么成效
谢谢你的回答，但我有一个疑问，我是否应该在现场调用validate或invalidate方法？可能是hello arunabha的复制品，这方面运气好吗？