Symfony\Component\Form\Extension\Core\Type\FileType::buildForm PHP Method

    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        if ($options['multiple']) {
            $builder->addEventListener(FormEvents::PRE_SUBMIT, function (FormEvent $event) {
                $form = $event->getForm();
                $data = $event->getData();

                // submitted data for an input file (not required) without choosing any file
                if (array(null) === $data) {
                    $emptyData = $form->getConfig()->getEmptyData();

                    $data = is_callable($emptyData) ? call_user_func($emptyData, $form, $data) : $emptyData;
                    $event->setData($data);
                }
            });
        }
    }

 /**
  * {@inheritdoc}
  */
 public function buildForm(FormBuilderInterface $builder, array $options)
 {
     parent::buildForm($builder, $options);
     $builder->setAttribute('uploadtype', $options['uploadtype']);
     $builder->setAttribute('placeholdWidth', $options['placeholdWidth']);
     $builder->setAttribute('placeholdHeight', $options['placeholdHeight']);
     $builder->setAttribute('placeholdText', $options['placeholdText']);
     $builder->setAttribute('ratio', $options['ratio']);
     $builder->setAttribute('pattern', $options['pattern']);
 }