Name: el35337 Date: 09/30/98


(Swing 1.1b2, JDK 1.1.5, 1.1.6, 1.1.7)
Although removing an element from a JList's underlying
ListModel causes that element's representation to
disappear from the view, ListSelectionEvent listeners
are not informed despite the fact that the selection
state of the view has changed.

The following code displays a frame containing a
JList view on a small model; a button; and a text area.
The text area is fed with string equivalents of
ListSelectionEvents heard from the JList, and the button
removes the item currently selected in the list, by manipulating
the model directly. No ListSelectionEvent is
detected when the button is used - I believe this to
be a bug.

import com.sun.java.swing.*;
import com.sun.java.swing.border.*;
import com.sun.java.swing.event.*;
import java.awt.*;
import java.awt.event.*;


public class ListDeselectionDemonstrator {

static final JTextArea eventDisplay = new JTextArea(10, 40);
static final String LINE_SEPARATOR = System.getProperty("line.separator");

public static void main(String[] args) {

JFrame frame = new JFrame("List deselection by model change: event-firing bug");
Container cont = frame.getContentPane();
cont.setLayout(new BorderLayout());

final DefaultListModel model = new DefaultListModel();
model.addElement("Item zero"); // let default renderer do its job
model.addElement("Item one");
model.addElement("Item two");

final JList list = new JList(model);
list.setBorder(BorderFactory.createBevelBorder(BevelBorder.LOWERED));

list.addListSelectionListener(new ListSelectionListener() {
public void valueChanged(ListSelectionEvent lse) {
echoText(lse.toString());
}
});

eventDisplay.setBorder(BorderFactory.createBevelBorder(BevelBorder.LOWERED));

JButton removeButton = new JButton("Remove element");
removeButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
int selectedIndex = list.getSelectedIndex();
if (selectedIndex == - 1) {
echoText("Nothing selected.");
return;
}

// For this example, we're validly assuming a model/view index match.
model.removeElementAt(selectedIndex); // should fire event
}
});

cont.add(list, BorderLayout.WEST);
cont.add(new JScrollPane(eventDisplay), BorderLayout.CENTER);
cont.add(removeButton, BorderLayout.SOUTH);

frame.setSize(500,500);
frame.setVisible(true);
}

static void echoText(String message) {
eventDisplay.append(message + LINE_SEPARATOR);

// Scroll to show appended text (thanks to Eric Tavares):
try { eventDisplay.setCaretPosition(eventDisplay.getDocument().getLength()); }
catch (IllegalArgumentException e) {}
}
}
(Review ID: 39713)
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