Symfony Event Listener to send html mail using SwiftMailer and Twig

ContractController.php

<?php

namespace Acme\Bundle\ContractBundle\Controller;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;

class ContractController extends Controller
{
    public function eventAction(Contract $contract)
    {
        $event = new ContractEvent($contract);

        $dispatcher = $this->get('event_dispatcher');
        $dispatcher->dispatch(
            ContractEvents::CONTRACT_CREATED,
            $event
        );

        return $this->render('AcmeContractBundle:Contract:index.html.twig', array(
            'contract' => $contract
        ));
    }
}

ContractEvent.php

<?php

namespace Acme\Bundle\ContractBundle\Event;

use Symfony\Component\EventDispatcher\Event;
use Acme\Bundle\ContractBundle\Entity\Contract;

class ContractEvent extends Event
{
    protected $contract;

    public function __construct(Contract $contract)
    {
        $this->contract = $contract;
    }

    public function getContract()
    {
        return $this->contract;
    }
}

ContractEvents.php

<?php

namespace Acme\Bundle\ContractBundle;

final class ContractEvents
{
    const CONTRACT_CREATED = 'contract.created';
}

ContractListener.php

<?php

namespace Acme\Bundle\ContractBundle\Event;

use Acme\Bundle\ContractBundle\Event\ContractEvent;

class ContractListener
{
    protected $twig;
    protected $mailer;

    public function __construct(\Twig_Environment $twig, \Swift_Mailer $mailer)
    {
        $this->twig = $twig;
        $this->mailer = $mailer;
    }

    public function onContractCreated(ContractEvent $event)
    {
        $contract = $event->getContract();

        $body = $this->renderTemplate($contract);

        $projectManager = $contract->getProjectManager();

        $message = \Swift_Message::newInstance()
            ->setSubject('Contract ' . $contract->getId() . ' created')
            ->setFrom('[email protected]')
            ->setTo('[email protected]')
            ->setBody($body)
        ;
        $this->mailer->send($message);
    }

    public function renderTemplate($contract)
    {
        return $this->twig->render(
            'AcmeContractBundle:Contract:mailer.html.twig',
            array(
                'contract' => $contract
            )
        );
    }
}

services.yml

services:
    contract_bundle.listener.contract:
        class: Acme\Bundle\ContractBundle\Event\ContractListener
        arguments:
            templating: "@twig"
            mailer: "@mailer"            
        tags:
            - { name: kernel.event_listener, event: contract.approved, method: onCommentEvent }