Preview Mode

The Contao Managed Edition comes with an additional preview.php entry point. This entry point is either accessible via a back end login, or a valid preview link.

When this entry point is accessed with a back end login, it offers features like logging in as a front end member or showing hidden elements.

To check whether code (content element, front end module, etc.) is currently executed within the preview entry point you can check for the _preview request attribute.

class FoobarController extends AbstractContentElementController
{
    protected function getResponse(Template $template, ContentModel $model, Request $request): Response
    {
        if ($request->attributes->get('_preview')) {
            // Execute some code within the preview entry point
        }

        return $template->getResponse();
    }
}

{% if app.request.attributes._preview|default %}
    {# Show some content within the preview entry point #}
{% endif %}

This however, does not check for the actual preview mode, which is activated by selecting Unpublished: show in the preview toolbar - or by accessing the preview entry with a valid preview link that has this feature enabled. To check for this, you can use the TokenChecker service.

use Contao\CoreBundle\Security\Authentication\Token\TokenChecker;

class FoobarController extends AbstractContentElementController
{
    public function __construct(private readonly TokenChecker $tokenChecker)
    {
    }

    protected function getResponse(Template $template, ContentModel $model, Request $request): Response
    {
        if ($this->tokenChecker->isPreviewMode()) {
            // Execute some code when the preview mode is active
        }

        return $template->getResponse();
    }
}

since 5.3 This is also available via the contao global Twig variable:

{% if contao.is_preview_mode %}
    {# Show some content only available in the preview mode #}
{% endif %}