@Override
        public void propertyChange(PropertyChangeEvent evt) {
          if (ContentImpl.PROP_CONTENT_MANAGER.equals(evt.getPropertyName())) {
            ContentManager oldValue = (ContentManager)evt.getOldValue();
            ContentManager newValue = (ContentManager)evt.getNewValue();
            if (oldValue != null) oldValue.removeContentManagerListener(BaseContentCloseListener.this);
            if (newValue != null) newValue.addContentManagerListener(BaseContentCloseListener.this);
          }
        }
@Override
        public void propertyChange(PropertyChangeEvent evt)