我是黑莓开发的新手。当我单击任何列表项时，我想添加一个复选框或勾选标记。当我尝试运行时，会出现 104 错误。
public final class ListDemoScreen extends MainScreen {
private Vector _listElements;
private int LEFT_OFFSET = 10;
private int TOP_OFFSET = 10;
ListField list;
private ListField _checkList;
private MenuItem _toggleItem;
public ListDemoScreen() {
super(Manager.NO_VERTICAL_SCROLL);
// Set the displayed title of the screen
setTitle("List Demo 1");
add(new LabelField("Fruits List", LabelField.FIELD_HCENTER));
add(new SeparatorField());
_listElements = new Vector();
add(new SeparatorField());
list = new ListField();
ListCallback _callback = new ListCallback(this);
list.setCallback(_callback);
list.setSize(4);
int index = list.getSelectedIndex();
add(list);
createField();
}
protected void createField() {
String itemOne = "Apple";
String itemTwo = "Blackberry";
String itemthree = "Grapes";
String itemfour = "Banana";
_listElements.addElement(itemOne);
_listElements.addElement(itemTwo);
_listElements.addElement(itemthree);
_listElements.addElement(itemfour);
reloadList();
}
private void reloadList() {
list.setSize(_listElements.size());
}
public boolean invokeAction(int action) {
switch (action) {
case ACTION_INVOKE: // Trackball click.
int index = list.getSelectedIndex();
ChecklistData data = (ChecklistData) _listElements.elementAt(index);
data.toggleChecked();
_listElements.setElementAt(data, index);
list.invalidate(index);
return true; // We've consumed the event.
}
return super.invokeAction(action);
}
class ListCallback implements ListFieldCallback {
ListDemoScreen listDemoScreen;
public ListCallback(ListDemoScreen listDemoScreen)
{
this.listDemoScreen=listDemoScreen;
}
public void drawListRow(ListField list, Graphics g, int index, int y,
int w) {
String text = (String) _listElements.elementAt(index);
g.drawText(text, 60, y + 5, 0, w);
text = (String) _listElements.elementAt(index);
Bitmap bitm = Bitmap.getBitmapResource("bullet_arrow.png");
int xpos = LEFT_OFFSET;
int ypos = TOP_OFFSET + y;
w = bitm.getWidth();
int h = bitm.getHeight();
g.drawBitmap(xpos, ypos, w, h, bitm, 0, 0);
xpos = w + 20;
ChecklistData currentRow = (ChecklistData)this.get(list, index);
StringBuffer rowString = new StringBuffer();
// If it is checked draw the String prefixed with a checked box,
// prefix an unchecked box if it is not.
if (currentRow.isChecked()) {
rowString.append(Characters.BALLOT_BOX_WITH_CHECK);
} else {
rowString.append(Characters.BALLOT_BOX);
}
// Append a couple spaces and the row's text.
rowString.append(Characters.SPACE);
rowString.append(Characters.SPACE);
rowString.append(currentRow.getStringVal());
// Draw the text.
g.drawText(rowString.toString(), 0, y, 0, w);
}
public Object get(ListField list, int index) {
return _listElements.elementAt(index);
}
public int indexOfList(ListField list, String prefix, int string) {
return _listElements.indexOf(prefix, string);
}
public int getPreferredWidth(ListField list) {
return Display.getWidth();
}
}
private class ChecklistData {
private String _stringVal;
private boolean _checked;
/*
* ChecklistData() { _stringVal = ""; _checked = false; }
*/
ChecklistData(String stringVal, boolean checked) {
_stringVal = stringVal;
_checked = checked;
}
// Get/set methods.
private String getStringVal() {
return _stringVal;
}
private boolean isChecked() {
return _checked;
}
/*
* private void setStringVal(String stringVal) { _stringVal = stringVal;
* }
*
* private void setChecked(boolean checked) { _checked = checked; }
*/
// Toggle the checked status.
private void toggleChecked() {
_checked = !_checked;
}
}
/* (non-Javadoc)
* @see net.rim.device.api.ui.container.MainScreen#makeMenu(net.rim.device.api.ui.component.Menu, int)
*/
protected void makeMenu(Menu menu, int instance) {
// TODO Auto-generated method stub
Field focus = UiApplication.getUiApplication().getActiveScreen().getLeafFieldWithFocus();
if(focus == _checkList)
{
//The _checkList ListField instance has focus.
//Add the _toggleItem MenuItem.
menu.add(_toggleItem);
}
super.makeMenu(menu, instance);
}
}