如何选择我在列表字段中添加的下拉菜单？

Question

朋友在我的BlackBerry应用程序中我使用列表字段，并在此列表字段我添加一个下拉列表。现在我的问题是如何选择我在列表Field.Now上添加的下拉列表我只选择列表字段而不是下拉列表但我的要求是首先我应该选择下拉列表然后列出字段。我在这里包含了我的代码，请检查一下。

public class TaskListField extends ListField implements ListFieldCallback, KeypadListener {
   private Vector rows;
   private Bitmap p1;
   private Bitmap p2;
   public LoginPage objLoginPage;

   public String[] data={"Call","Visit"};

   public String strIndex = null;
   public int tempIndex = 0;
   public int intvalue;
   public int id;
   public int value;
   public boolean hasFocus = false;
   public static String[] arrOutletName = { "Dosa Store", "Benfish Bhawan",
      "Nalban Park", "Korunamoyee", "206 Bus Stop", "aaaaaaaa",
      "bbbbbbbb", "ccccccccc", "dddddddd", "eeeeeee" };


   public ObjectChoiceField ocf;

   public TaskListField() {
      super(0, ListField.MULTI_SELECT);
      setRowHeight(80);
      setEmptyString("Hooray, no tasks here!", DrawStyle.HCENTER);
      setCallback(this);

      p1 = Bitmap.getBitmapResource("name.png");
      p2 = Bitmap.getBitmapResource("name.png");

      rows = new Vector();

      for (int x = 0; x < XmlHander.vectSrno.size(); x++) {
         TableRowManager row = new TableRowManager();

         strIndex = String.valueOf(x);
         String strVectno = XmlHander.vectSrno.elementAt(x).toString();
         String strSLADate = XmlHander.vectSldate.elementAt(x).toString();

         if (x % 2 == 0) {
            row.add(new BitmapField(null));
         }
         else {
            row.add(new BitmapField(null));
         }


         LabelField task = new LabelField(" ");

         if (x % 15 == 0) {
            task.setFont(Font.getDefault().derive(Font.BOLD | Font.UNDERLINED));
         } else {
            task.setFont(Font.getDefault().derive(Font.BOLD));
         }
         row.add(task);

         row.add(new LabelField(strVectno, DrawStyle.ELLIPSIS) {
            protected void paint(Graphics graphics) {
               graphics.setColor(0x00878787);
               // graphics.setColor(Color.PINK);
               super.paint(graphics);
            }
         });

         row.add(ocf=new ObjectChoiceField("",data){

            protected void paint(Graphics graphics){

               graphics.setColor(0x00878787);
               super.paint(graphics);
            }
         });

         ocf.setChangeListener(new FieldChangeListener(){

            public void fieldChanged(Field field, int context) {
               if(context != PROGRAMMATIC)
                  Dialog.alert(data[ocf.getSelectedIndex()]);
            }
         });

         rows.addElement(row);

      }
      setSize(rows.size());
   }


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

      rowManager.drawRow(g, 0, y, width, list.getRowHeight());
   }

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

      public void drawRow(Graphics g, int x, int y, int width, int height) {

         layout(width, height);

         setPosition(x, y);

         g.pushRegion(getExtent());

         subpaint(g);

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

         g.popContext();
      }

      protected void sublayout(int width, int height) {

         int fontHeight = Font.getDefault().getHeight();
         int preferredWidth = getPreferredWidth();

         Field field = getField(0);
         layoutChild(field, 32, 32);
         setPositionChild(field, 0, 0);

         field = getField(1);
         layoutChild(field, preferredWidth - 16, fontHeight + 1);
         setPositionChild(field, 34, 3);

         field = getField(2);
         layoutChild(field, 150, fontHeight + 1);
         setPositionChild(field, 34, fontHeight + 6);

         field = getField(3);
         layoutChild(field, 150, fontHeight + 1);
         setPositionChild(field, preferredWidth - 152, fontHeight + 6);

         setExtent(preferredWidth, getPreferredHeight());
      }

      public int getPreferredWidth() {
         return Graphics.getScreenWidth();
      }

      public int getPreferredHeight() {
         return getRowHeight();
      }
   }

   public Object get(ListField listField, int index) {

      return null;
   }

   public int getPreferredWidth(ListField listField) {

      return 0;
   }

   public int indexOfList(ListField listField, String prefix, int start) {

      return 0;
   }

   protected boolean navigationClick(int status, int time) {
      final int index;
      index = this.getFieldWithFocusIndex() - 1;

      UiApplication.getUiApplication().invokeLater(new Runnable() {
         public void run() {

            UiApplication.getUiApplication().pushScreen(new Details(id));
         }
      });

      return false;
   }

   public int moveFocus(int amount, int status, int time) {

      invalidate(getSelectedIndex());
      id = this.getSelectedIndex();
      invalidate();

      return super.moveFocus(amount, status, time);
   }

   public void onFocus(int direction) {

      hasFocus = true;
      super.onFocus(direction);
      System.out.println("direction==" + direction);
      invalidate();
   }

   public void onUnfocus() {

      updateLayout();
      super.onUnfocus();
      invalidate();
   }

   private int getFieldWithFocusIndex() {
      return 0;
   }

}