Handler

abstract class Handler
{
	protected $form;

	protected $formFactory;

	protected $data;

	protected $request;

	protected $router;

	protected $twig;

	protected $flashBag;

	public function __construct(Form $form, Request $request, FormFactory $formFactory, RouterInterface $router, Environment $twig, FlashBagInterface $flashBag)
	{
		$this->form = $form;
		$this->formFactory = $formFactory;
		$this->request = $request;
		$this->router = $router;
		$this->twig =$twig;
		$this->flashBag =$flashBag;

	}

	public function onCreate(): FormInterface
	{
		$this->form = $this->formFactory->create($this->getFormType(), $this->data, $this->getFormOptions());
		return $this->form;
	}

	public function handle($data = null, $request)
	{
		$this->data = $data;
		$this->request = $request;

		$this->onCreate()->handleRequest($request);

		if ($this->form->isSubmitted() && $this->form->isValid()) {

			return true;
		}

		return false;

	}

	public function getFormOptions(): array
	{
		return [];
	}

	public abstract static function getFormType(): string;

TaskController

public function createTask(
        Request $request,
        Security $security,
        FormFactory $formFactory,
        Session $session,
        RouterInterface $router,
		TaskHandler $taskHandler
    ): Response {

		$taskHandler->handle(new Task(), $request);

        // On récupère l 'utilisateur de la session
        $user = $security->getUser();

		if ($taskHandler->onSuccess()){

            // On attribut le 'username' de la session  à la tache créée
            //$task->setUser($user);

            $session->getFlashBag()->add('success', 'La tâche a été bien été ajoutée.');
            return new RedirectResponse($router->generate('task_list'));
        }

        return new Response($this->twig->render(
            'task/create.html.twig',
            ['form' => $taskHandler->onCreate()->createView()]
        ));
    }

TaskHandler

class TaskHandler extends Handler
{

	private $entityManager;

	public function __construct(
		Form $form,
		Request $request,
		FormFactory $formFactory,
		RouterInterface $router,
		Environment $twig,
		FlashBagInterface $flashBag,
		EntityManager $entityManager
	) {
		parent::__construct($form, $request, $formFactory, $router, $twig, $flashBag);
		$this->entityManager = $entityManager;
	}


	public static function getFormType(): string
	{
		return TaskType::class;
	}


	public function onSuccess(): Response
	{
		$task = $this->form->getData();
		$this->entityManager->persist($task);
		$this->entityManager->flush();
	}