Why does the check box untick itself?

Question

I have a program which has a GUI control that I designed. It consists of several check boxes inside a panel, the user can tick one or more of them. There are various methods to get all the selections, untick boxes in code etc. In one place in my software, I need a dialog box to appear when the user ticks a box. So I got my control to raise a property change event whenever one of the check boxes is ticked or unticked. I then catch this in another part of the code, and cause a dialog to appear which asks the user for further options.
My problem is this: for some strange reason, when the dialog appears, it is causing the check box to be unticked again immediately after it is ticked. I have prepared a simplified version of the problem code, below. If you comment out the call to ticking(), then it works ok (but the dialog doesn't appear obviously). Has anyone got any ideas, please?
import java.awt.GridLayout;
import java.awt.event.*;
import java.beans.*;
import java.util.HashSet;
import javax.swing.*;
public class Testing {
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            @Override public void run() {                 
                Testing testing = new Testing();
    public Testing() {
        JFrame fmMain = new JFrame();
        CheckBoxes cb = new CheckBoxes("one", "two", "three");
        cb.addPropertyChangeListener(new PropertyChangeListener() {    
            @Override public void propertyChange(PropertyChangeEvent pce) {
                String category = (String) pce.getPropertyName();
                if(category.equals("ticking")) {            
                    ticking();  //commenting this out means the boxes are ticked ok
        fmMain.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
        fmMain.add(cb);
        fmMain.pack();
        fmMain.setVisible(true);
    private void ticking() {
        final JDialog dlg = new JDialog();
        JButton okbutton = new JButton("OK");
        okbutton.addActionListener(new ActionListener() {
            @Override public void actionPerformed(ActionEvent ae) {
                dlg.dispose();
        dlg.add(okbutton);
        dlg.setModal(true);
        dlg.pack();
        dlg.setVisible(true); 
    class CheckBoxes extends JScrollPane {
        public CheckBoxes(Object... arr) {
            super();
            GridLayout gl = new GridLayout();
            gl.setColumns(1);
            JPanel panel = new JPanel();
            setViewportView(panel);
            gl.setRows(arr.length);
            panel.setLayout(gl);
            ItemListener cl = new ItemListener() {
                @Override public void itemStateChanged(ItemEvent ie) {
                    JCheckBox cbi = (JCheckBox) ie.getSource();
                    String propertyName = cbi.isSelected() ? "ticking" : "unticking";     
                    System.out.println("Item event: "+propertyName);
                    CheckBoxes.this.firePropertyChange(propertyName, null, cbi.getText());
            HashSet data = new HashSet();
            for(Object o: arr) {
                if(!data.contains(o)) {
                    JCheckBox candidate = new JCheckBox(o.toString());
                    panel.add(candidate);
                    candidate.addItemListener(cl);
                    data.add(o);
}

Answer 1

Thanks Malcolm, I used the different thread as you suggested and it works fine :).
import java.awt.EventQueue;
import java.awt.GridLayout;
import java.awt.event.*;
import java.beans.*;
import java.util.HashSet;
import javax.swing.*;
public class Testing {
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            @Override public void run() {                 
                Testing testing = new Testing();
    public Testing() {
        JFrame fmMain = new JFrame();
        CheckBoxes cb = new CheckBoxes("one", "two", "three");
        cb.addPropertyChangeListener(new PropertyChangeListener() {    
            @Override public void propertyChange(PropertyChangeEvent pce) {
                String category = (String) pce.getPropertyName();
                if(category.equals("ticking")) {   
                    ShowDlg sd = new ShowDlg();
                    EventQueue.invokeLater(sd);
        fmMain.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
        fmMain.add(cb);
        fmMain.pack();
        fmMain.setVisible(true);
    class CheckBoxes extends JScrollPane {
        public CheckBoxes(Object... arr) {
            super();
            GridLayout gl = new GridLayout();
            gl.setColumns(1);
            JPanel panel = new JPanel();
            setViewportView(panel);
            gl.setRows(arr.length);
            panel.setLayout(gl);
            ItemListener cl = new ItemListener() {
                @Override public void itemStateChanged(ItemEvent ie) {
                    JCheckBox cbi = (JCheckBox) ie.getSource();
                    String propertyName = cbi.isSelected() ? "ticking" : "unticking";     
                    System.out.println("Item event: "+propertyName);
                    CheckBoxes.this.firePropertyChange(propertyName, null, cbi.getText());
            HashSet data = new HashSet();
            for(Object o: arr) {
                if(!data.contains(o)) {
                    JCheckBox candidate = new JCheckBox(o.toString());
                    panel.add(candidate);
                    candidate.addItemListener(cl);
                    data.add(o);
    class ShowDlg implements Runnable {
        @Override public void run() {
            final JDialog dlg = new JDialog();
            JButton okbutton = new JButton("OK");
            okbutton.addActionListener(new ActionListener() {
                @Override public void actionPerformed(ActionEvent ae) {
                    dlg.dispose();
            dlg.add(okbutton);
            dlg.setModal(true);
            dlg.pack();
            dlg.setVisible(true); 
}Edited by: 892190 on 19-Oct-2011 08:02