Silex: populate form with entered data after invalid submit - twig

Question

After the user submits a (uncomplete) form, I want the form to show the already entered data + an error message.
Using this code, the form is empty after submitting the form:
$request = $app['request'];
$form = $app['form.factory']->createBuilder('form')
->add('name', 'text', array( 'label' => 'Ihre Name:'))
->add('comment', 'text', array('constraints' => new Assert\Length(array('min' => 15))))
->getForm();
$twig_context = array('form' => $form->createView());
$form->handleRequest($request);
if ($form->isValid()) {
$data = $form->getData();
return 'valid!';
// Send form...
} else {
// display the form
return $app['twig']->render('contact.html.twig', $twig_context);
}
Twig-template:
{{ form_start(form) }}
{{ form_widget(form) }}
<div>
<input type="submit" value="Send" />
</div>
{{ form_end(form) }}

Answer 1

You should create the form view last, (could be right before you render your template). In your case, the view is created before the data from Request is applied.
This:
$twig_context = array('form' => $form->createView());
$form->handleRequest($request);
Should be:
$form->handleRequest($request);
And your render method should be:
return $app['twig']->render('contact.html.twig',
array(
'form' => $form->createView()
)
);