6. Showing image previews

This is a full working example of one way to add image previews to your create and edit views in SonataAdmin.

6.1. Pre-requisites

• you have already got the image files on a server somewhere and have a helper method to retrieve a publicly visible URL for that image, in this example that method is called Image::getWebPath()

• you have already set up an Admin to edit the object that contains the images, now you want to add the previews. In this example that class is called ImageAdmin

Note

There is a separate cookbook recipe to demonstrate how to upload images (and other files) using SonataAdmin.

6.2. The recipe

You can use Symfony ‘help’ and ‘help_html’ options to put raw HTML into any given form field. We are going to use this functionality to embed an image tag when an image exists.

To do this we need to:

• get access to the Image instance from within ImageAdmin

• create an image tag based on the Image’s URL

• add a ‘help’ and ‘help_html’ option to a field on the Image form to display the image tag

For the sake of this example we will use some basic CSS to restrict the size of the preview image (we are not going to generate and save special thumbnails).

6.2.1. Basic example - for single layer Admins

If we are working directly with our ImageAdmin class then getting hold of the Image instance can be done by calling $this->getSubject(). Since we are manipulating form fields we do this from within ImageAdmin::configureFormFields():

final class ImageAdmin extends AbstractAdmin
{
    protected function configureFormFields(FormMapper $form): void
    {
        // get the current Image instance
        $image = $this->getSubject();

        // use $fileFormOptions so we can add other options to the field
        $fileFormOptions = ['required' => false];
        if ($image && ($webPath = $image->getWebPath())) {
            // get the request so the full path to the image can be set
            $request = $this->getRequest();
            $fullPath = $request->getBasePath().'/'.$webPath;

            // add a 'help' option containing the preview's img tag
            $fileFormOptions['help'] = '<img src="'.$fullPath.'" class="admin-preview"/>';
            $fileFormOptions['help_html'] = true;
        }

        $form
            ->add('file', 'file', $fileFormOptions)
        ;
    }
}

We then use CSS to restrict the max size of the image:

img.admin-preview {
    max-height: 200px;
    max-width: 200px;
}

And that is all there is to it!

However, this method does not work when the ImageAdmin can be embedded in other Admins using the Sonata\\AdminBundle\\Form\\Type\\AdminType field type. For that we need…

6.2.2. Advanced example - works with embedded Admins

When one Admin is embedded in another Admin, $this->getSubject() does not return the instance under management by the embedded Admin. Instead we need to detect that our Admin class is embedded and use a different method:

final class ImageAdmin extends AbstractAdmin
{
    protected function configureFormFields(FormMapper $form): void
    {
        if($this->hasParentFieldDescription()) { // this Admin is embedded
            // $getter will be something like 'getlogoImage'
            $getter = 'get' . $this->getParentFieldDescription()->getFieldName();

            // get hold of the parent object
            $parent = $this->getParentFieldDescription()->getAdmin()->getSubject();
            if ($parent) {
                $image = $parent->$getter();
            } else {
                $image = null;
            }
        } else {
            $image = $this->getSubject();
        }

        // use $fileFormOptions so we can add other options to the field
        $fileFormOptions = ['required' => false];
        if ($image && ($webPath = $image->getWebPath())) {
            // add a 'help' option containing the preview's img tag
            $fileFormOptions['help'] = '<img src="'.$webPath.'" class="admin-preview"/>';
            $fileFormOptions['help_html'] = true;
        }

        $form
            ->add('file', 'file', $fileFormOptions)
        ;
    }
}

As you can see, the only change is how we retrieve set $image to the relevant Image instance. When our ImageAdmin is embedded we need to get the parent object first then use a getter to retrieve the Image. From there on, everything else is the same.

6.3. Notes

If you have more than one level of embedding Admins this will (probably) not work. If you know of a more generic solution, please fork and update this recipe on GitHub. Similarly, if there are any errors or typos (or a much better way to do this) get involved and share your insights for the benefit of everyone.