/**
     * Function called when an audio device is plugged or unplugged.
     *
     * @param event The property change event which may concern the audio device.
     */
    public void propertyChange(PropertyChangeEvent event) {
      if (DeviceConfiguration.PROP_AUDIO_SYSTEM_DEVICES.equals(event.getPropertyName())) {
        NotificationService notificationService = getNotificationService();

        if (notificationService != null) {
          // Registers only once to the  popup message notification
          // handler.
          if (!isRegisteredToPopupMessageListener) {
            isRegisteredToPopupMessageListener = true;
            managePopupMessageListenerRegistration(true);
          }

          // Fires the popup notification.
          ResourceManagementService resources = NeomediaActivator.getResources();
          Map<String, Object> extras = new HashMap<String, Object>();

          extras.put(NotificationData.POPUP_MESSAGE_HANDLER_TAG_EXTRA, this);
          notificationService.fireNotification(
              DEVICE_CONFIGURATION_HAS_CHANGED,
              resources.getI18NString("impl.media.configform" + ".AUDIO_DEVICE_CONFIG_CHANGED"),
              resources.getI18NString(
                  "impl.media.configform" + ".AUDIO_DEVICE_CONFIG_MANAGMENT_CLICK"),
              null,
              extras);
        }
      }
    }
  /**
   * Returns the <tt>NotificationService</tt> obtained from the bundle context.
   *
   * @return The <tt>NotificationService</tt> obtained from the bundle context.
   */
  public static NotificationService getNotificationService() {
    if (notificationService == null) {
      // Get the notification service implementation
      ServiceReference notifReference =
          bundleContext.getServiceReference(NotificationService.class.getName());

      notificationService = (NotificationService) bundleContext.getService(notifReference);

      if (notificationService != null) {
        // Register a popup message for a device configuration changed
        // notification.
        notificationService.registerDefaultNotificationForEvent(
            DEVICE_CONFIGURATION_HAS_CHANGED,
            net.java.sip.communicator.service.notification.NotificationAction.ACTION_POPUP_MESSAGE,
            "Device onfiguration has changed",
            null);
      }
    }

    return notificationService;
  }