php - Extend controller - but how activate it? (Symfony 2) -

i want use code in application:

class controllerextension extends symfony\bundle\frameworkbundle\controller\controller  {     public function render($view, array $parameters = array(), response $response = null)     {          //etc.      }  } 

but put , how activate it? i'm guessing it's services.yml file. i've used event listeners, different.

from code snippet (http://justpaste.it/2caz), seems missed "return" keyword in call parent.

class controllerextension extends symfony\bundle\frameworkbundle\controller\controller  {     public function render($view, array $parameters = array(), response $response = null)     {         if($this->getrequest()->getrequestformat() == 'json') {             return new response(json_encode($parameters));         } else {             // missing 'return' in snippet             return parent::render($view, $parameters, $response);         }     }  }  class mycontroller extends controllerextension {     public function indexaction()     {         // should work         return $this->render(...);     } }