Symfony 2 ajax

<?
//Controller:

 if ($this->getRequest()->isXmlHttpRequest())
        {
            $response = new JsonResponse();
            $response->setData(array(
                'title' => $title,
                'data' => $this->render('AcmeMainBundle:Default:index.html.twig'
                )
            ));

            return new JsonResponse(array(
                'title' => $title,
                'data' => $this->render('AcmeMainBundle:Default:index.html.twig'
                )));
            //return $response;
        }
 return $this->render('SothysMainBundle:Default:index.html.twig');

//Twig:

{% extends app.request.xmlHttpRequest
? 'AcmeMainBundle:Default:ajax-layout.html.twig'
: 'AcmeMainBundle:Default:layout.html.twig' %}