ErrorPageLoadedEvent example

$page = ErrorPage::createFrom($page);

        /** @var CmsPageCollection $pages */
        $pages = $this->cmsPageLoader->load($request, new Criteria([$cmsErrorLayoutId]), $context)->getEntities();

        if (!$pages->has($cmsErrorLayoutId)) {
            throw new PageNotFoundException($cmsErrorLayoutId);
        }

        $page->setCmsPage($pages->get($cmsErrorLayoutId));

        $this->eventDispatcher->dispatch(new ErrorPageLoadedEvent($page, $context, $request));

        return $page;
    }
}