protected String changePressed() {
   if (change == null) return null;
   Properties p = new Properties();
   p.put("shell", bar.getControl().getShell()); // $NON-NLS-1$
   change.setObject(p);
   int i = change.execute();
   if (i != 0) return null;
   return p.getProperty("value"); // $NON-NLS-1$
 }
 protected Control getChangeControl(Composite parent) {
   if (bar.getControl() != null && !bar.getControl().isDisposed()) {
     return bar.getControl();
   }
   return bar.createControl(parent);
 }