public function onRoute(MvcEvent $event)
    {
        /* @var \Zend\Http\PhpEnvironment\Request $request */
        $request = $event->getRequest();
        $ajax = $request->getQuery()->get('ajax');

        if (!$request->isXmlHttpRequest() || !$ajax) {
            /* no ajax request or required parameter not present */
            return;
        }

        /* @var \Zend\Http\PhpEnvironment\Response $response */
        /* @var AjaxEvent $ajaxEvent */
        $response = $event->getResponse();
        
        $ajaxEvent = $this->ajaxEventManager->getEvent($ajax, $this);
        $ajaxEvent->setRequest($request);
        $ajaxEvent->setResponse($response);

        $results = $this->ajaxEventManager->triggerEventUntil(function ($r) {
            return null !== $r;
        }, $ajaxEvent);
        $result  = $results->last() ?: $ajaxEvent->getResult();

        if (!$result) {
            throw new \UnexpectedValueException('No listener returned anything. Do not know what to do...');
        }

        /* Convert arrays or traversable objects to JSON string. */
        if (is_array($result) || $result instanceof \Traversable) {
            $result = Json::encode($result, true, ['enableJsonExprFinder' => true]);
        }

        $contentType = $ajaxEvent->getContentType();

        $response->getHeaders()->addHeaderLine('Content-Type', $contentType);
        $response->setContent($result);

        return $response;
    }