How to clear field value with Symfony2 forms

Question

I'm writing my own CAPTCHA class and when the form doesn't validate, I don't want to pre-populate the captcha input with the previous answer, for obvious reasons. I just want to the clear the input before it's rendered.

I've discovered the data option is only for the default value, which is overwritten by what the user enters. I tried the following code:

$form->get('captcha')->setData(null);

.. After the request is bound with the form, but an AlreadyBoundException is thrown. I have actually managed to get it working with:

if (isset($formView->children['captcha'])) {
    $formView->children['captcha']->vars['value'] = null;
}

But that just looks wrong, and definitely not up to Symfony standards. I've looked through the other options you can provide when building the form, but I can't see anything of note.

Does anyone have any idea?

By the way, I half expect Symfony2 comes packaged with a CAPTCHA solution, this is mainly a learning exercise while I get used to the framework.

Answer 1

I think you want to handle this form field like Symfony handles a password field: it won't get populated. Let's take a look at the PasswordType:

namespace Symfony\Component\Form\Extension\Core\Type;

class PasswordType extends AbstractType
{
    public function buildView(FormView $view, FormInterface $form, array $options)
    {
        if ($options['always_empty'] || !$form->isSubmitted()) {
            $view->vars['value'] = '';
        }
    }

    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults(array(
            'always_empty' => true,
            'trim' => false,
        ));
    }

    //...
}

So, it's pretty simple: just add $view->vars['value'] = '' in the buildView method of your FormType (i.e. CaptchaType). That means the data of the field is not being cleared, but it won't be passed to the Twig template. Different approach, but the result is the same: the password field stays empty after validation failed.

If you are really lazy, you can use the PasswordType, but since the input of that field will be masked (*****), will that make an annoying captcha field even worse.

Your Form Type maybe look like this:

class CaptchaType extends AbstractType
{
    /**
     * {@inheritdoc}
     */
    public function buildView(FormView $view, FormInterface $form, array $options)
    {
        $view->vars['value'] = '';
    }

    /**
     * {@inheritdoc}
     */
    public function getParent()
    {
        return __NAMESPACE__.'\TextType';
    }

    /**
     * {@inheritdoc}
     */
    public function getName()
    {
        return $this->getBlockPrefix();
    }

    /**
     * {@inheritdoc}
     */
    public function getBlockPrefix()
    {
        return 'captcha';
    }
}

Edit: Just found that CaptchaBundle took the same approach.