Php Symfony/Silex表单生成器从未提交

我有一个细枝页面，用于呈现控制器中定义的表单：

$app->post('/thepath', function(Request $request) use ($app) {
    $app['request'] = $request;

    $token = $app['security.token_storage']->getToken();
    if (null !== $token) {
        $user = $token->getUser();


        $form = $app['form.factory']->createBuilder(FormType::class)
        ->add('firstname', TextType::class, [
            'required' => true,
        ])
        ->getForm();



        $form->handleRequest($request);

        if($form->isSubmitted() && $form->isValid()) {
            $data = $form->getData();

            // The code I want to run.
        }


        return $app['twig']->render('file.twig', [
            'form' => $form->createView(),
        ]);

    }

})->bind('thepath');

但是当我提交表格的时候

{{ form_start(form) }}
        {{ form_label(form.firstname) }}<br />
        {{ form_widget(form.firstname) }}<br />
        {{ form_errors(form.firstname) }}

    <input type="submit" value="Valider" />
{{ form_end(form) }}

if($form->isSubmitted()) { // is true
if($form->isValid()) { // is false