Symfony 4- VichUploader -如何删除编辑表单中的图像预览？

use Vich\UploaderBundle\Mapping\Annotation as Vich;

/**
 * @Vich\Uploadable
 */
class YourEntity
{
    /**
     * @Vich\UploadableField(mapping="your_mapping_name", fileNameProperty="imageName")
     *
     * @var File|null
     */
    private $imageFile;

    // ...
}

{{ form_start(form) }}

{% if form.imageFile.vars.value %}
    <img src="{{ vich_uploader_asset(form.imageFile.vars.value, 'your_mapping_name') }}" alt="Preview" />
    <label>{{ form.imageFile.vars.label }}</label>
    {{ form_widget(form.imageFile) }}
    <input type="checkbox" name="{{ form.imageFile.vars.full_name }}[delete]" /> Delete
{% else %}
    {{ form_row(form.imageFile) }}
{% endif %}

{{ form_end(form) }}

public function edit(Request $request, YourEntity $entity)
{
    $form = $this->createForm(YourEntityType::class, $entity);
    $form->handleRequest($request);

    if ($form->isSubmitted() && $form->isValid()) {
        // 删除图像
        if ($form->get('imageFile')->get('delete')->getData()) {
            $entity->setImageFile(null);
        }

        // 保存实体
        $entityManager = $this->getDoctrine()->getManager();
        $entityManager->persist($entity);
        $entityManager->flush();

        return $this->redirectToRoute('your_route');
    }

    return $this->render('your_template.html.twig', [
        'form' => $form->createView(),
    ]);
}