I use the code snippet from: render a drupal 8 entity in a string

$node = \Drupal::entityManager()->getStorage('node')->load($nodeid);
$view_builder = \Drupal::entityManager()->getViewBuilder('node');
$renderarray = $view_builder->view($node, 'full');
$html = \Drupal::service('renderer')->renderRoot($renderarray);

It works in a normal controller class without problems. But I did not get it to work in an Ajax Callback in a Custom Form.

The $html = \Drupal::service('renderer')->renderPlain($build); returns nothing.

Where ist the problem? Here is the reduced code of my test form:


namespace Drupal\mymodule\Form;

use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;

class SearchApiPageBlockForm extends FormBase {

  public function getFormId() {
    return 'search_api_page_block_form';

  public function buildForm(array $form, FormStateInterface $form_state, $args = array()) {

    $form['form']['actions'] = array('#type' => 'actions',);
    $form['form']['actions']['submit'] = array(
      '#type' => 'submit',
      '#value' => $this->t('TESTBUTTON!'),
      '#ajax' => array(
        'callback' => '::myAjaxCallback',

    return $form;

  public function submitForm(array &$form, FormStateInterface $form_state) {

  public function myAjaxCallback(array &$form, FormStateInterface $form_state) {

    $view_builder = \Drupal::entityTypeManager()->getViewBuilder('comment');
    $storage = \Drupal::entityTypeManager()->getStorage('comment');
    $node = $storage->load(103); //cid 103 already exists
    $build = $view_builder->view($node);

    dpm('before rendering'); // -> dpm output is: 'before rendering' 

    $html = \Drupal::service('renderer')->renderPlain($build);  

    dpm($html);// -> dpm has no output 
    dpm('after rendering');// -> dpm has no output



My goal is, to return the html of an entity via the

$response->addCommand(new HtmlCommand('#testtmp_message', $output));

UPDATE: Content of build: dpm(build)

enter image description here

  • The code seems to work, on a first quick look. Are you getting any errors (webserver longs or Drupal logger entries) ? Jan 30, 2017 at 9:41
  • Normally you don't need to render, did you try to use the build array for the ajax command? $response->addCommand(new HtmlCommand('#testtmp_message', $build));
    – 4uk4
    Jan 30, 2017 at 9:48
  • @Stefanos Petrakis I have enabled Home > Administration > Configuration > Development "All messages, with backtrace information" and added error_reporting(E_ALL); ini_set('display_errors', TRUE); ini_set('display_startup_errors', TRUE); in my settings.php but there were no errors reported.
    – userpixel
    Jan 30, 2017 at 12:28
  • @4k4 I tried to return the $build directly but nothing changes: $response->addCommand(new HtmlCommand('#testtmp_message', $build)); I tried a normal return array with success: $build = ['#type' => 'html_tag', '#tag' => 'p', '#value' => 'HERE',];
    – userpixel
    Jan 30, 2017 at 12:30
  • @userpixel, what is in $build? - btw. for reporting errors, often you don't see the error on screen when it is an ajax reponse, check the content of the response in the browser debugging tools.
    – 4uk4
    Jan 30, 2017 at 12:52

1 Answer 1


The code in my question is OK. The problem was caused by a conflict by calling the form from hook_preprocess_field(). I changed the hook, and I am calling the form from template_preprocess_block() and the AJAX callback of the entity gets fine.

4k4 put me on the right track. Thank you.

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