rendering symfony/form in non-symfony application - php

Question

I'm trying to rewrite a "custom framework" application to the Symfony, but I can not do everything at once, so I've divided the process into steps.
From important notes - I've already implemented the symfony/templating component and the symfony/twig-bridge component.
That's how I want to output the form in the template:
<?php echo $view['form']->form($form) ?>
As I'm doing so the following error is thrown:
Symfony\Component\Form\Exception\LogicException
No block "form" found while rendering the form.
/var/www/html/vendor/symfony/form/FormRenderer.php on line 98
To render the templates I'm using the DelegatingEngine which uses the PhpEngine and the TwigEngine.
Setting up the Twig with the \Symfony\Bridge\Twig\Extension\FormExtension is well documented, but what I'm missing is the php setup. This is how I'm doing this:
new \Symfony\Component\Form\Extension\Templating\TemplatingExtension($phpEngine, $this->csrfManager());
Could you point me what am I missing or what's wrong with my setup?

Answer 1

I think the simplest way would have been to install the Symfony 3.3 standard edition next to your app (pending the release of Symfony Flex).
After this, find a way to use the router of Symfony with the router of your application.
So you could have the full Symfony framework, create your form type in it and let Symfony render it :
With an ajax call
With a new Symfony Kernel in your legacy app

Answer 2

I've found the answer:
I was using the wrong FormRendererEngineInterface. Instead of relying on the \Symfony\Component\Form\Extension\Templating\TemplatingExtension class I've registered the form helper by myself:
$phpEngine = new PhpEngine(new TemplateNameParser(), new FilesystemLoader(realpath(__DIR__.'/../Template').'/%name%'));
$twigEngine = new TwigEngine($this->twig(), new TemplateNameParser());
$this->TemplateEngine = new DelegatingEngine(array(
$phpEngine,
$twigEngine,
));
$phpEngine->addHelpers(array(
new FormHelper(new FormRenderer($this->twigFormRendererEngine())),
));
As you can see in the TemplatingEngine:
public function __construct(PhpEngine $engine, CsrfTokenManagerInterface $csrfTokenManager = null, array $defaultThemes = array())
{
$engine->addHelpers(array(
new FormHelper(new FormRenderer(new TemplatingRendererEngine($engine, $defaultThemes), $csrfTokenManager)),
));
}
It relies on the TemplatingRendererEngine while I need the TwigRendererEngine instance, as the form templates are the twig files.
Correct me if my explanation is wrong, but the solution is working.