FooController.php

 class FooController
 {
     public function viewArticleAction($articleId)
     {
         $article = $this->articleRepository->getById($articleId);
         $parameters = array(
             'article' => $article,
         );

         // beginner
         return $this->handle($parameters, 'FooBundle:Foo:view.twig');

         // advanced
         $view = $this->view;
         $view->setParameters($parameters);
         $view->setTemplate('FooBundle:Foo:view.twig');
         return $view->handle($this->request);
     }
 }

 Example custom handler, note this could also be defined by extending the DefaultView class:

 class FooController
 {
     public function rssFeedAction()
     {
         // Could be done via DIC config
         $this->view->registerHandler('rss', array($this, 'handleRss'));

         $data = array('news' => $this->newsRepository->getLatestNews());

         // Could be done in the route
         $this->request->setRequestFormat('rss');

         $this->view->setParameters($data);
         return $this->view->handle($this->request);
     }

     public function handleRss($view, $request, $response)
     {
         $data = $view->getParameters();

         foreach ($data['news'] as $news) {
             // build feed content
         }

         $response->headers->set('Content-Type', 'text/xml');
         $response->setContent($feed);
         return $response;
     }
 }