Custom display_extender not able to use custom ajax callbacks inside options form

Question

i´m working on a custom display extender for Views.

The display extender itself works as expected, i´ve taken the code mostly from Studiogd The display extender plugin now i needed in the options form a fieldset with add more button, so i tried to implement/adapt \Drupal\form_api_example\Form\AjaxAddMore for my options form.

But i have a problem calling the submit and ajax callback.

Here is a subset of my display extender that is probalby relevant

namespace Drupal\foo\Plugin\views\display_extender;

use Drupal\views\Plugin\views\display_extender\DisplayExtenderPluginBase;
use Drupal\Core\Form\FormStateInterface;

/**
 * Foo display extender plugin.
 *
 * @ingroup views_display_extender_plugins
 *
 * @ViewsDisplayExtender(
 *   id = "foo",
 *   title = @Translation("Foo"),
 *   help = @Translation("Foo Bar."),
 *   no_ui = FALSE
 * )
 */
class Foo extends DisplayExtenderPluginBase {

  ...


  /**
   * Provide a form to edit options for this plugin.
   */
  public function buildOptionsForm(&$form, FormStateInterface $form_state) {
   
   ...

    $form['foo']['filters_fieldset']['actions']['add_filter'] = [
      '#type' => 'submit',
      '#value' => $this->t('Add an entry'),
      '#submit' => [
        '::addFilterEntry', // <---- Taken from example
      ],
      '#ajax' => [
        'callback' =>  '::filtersFieldsetCallback',
        'wrapper' => 'filters-fieldset-wrapper',
      ],
    ];

    ...
  }

  ...

  /**
   * Submit handler for the "add-one-more" button.
   *
   * Increments the max counter and causes a rebuild.
   */
  public function addFilterEntry(array &$form, FormStateInterface $form_state) {

    $filter_field = $form_state->get('num_filters');
    $add_button = $filter_field + 1;
    $form_state->set('num_filters', $add_button);

    // Since our buildForm() method relies on the value of 'num_filters' to
    // generate 'filter' form elements, we have to tell the form to rebuild. If we
    // don't do this, the form builder will not call buildForm().
    $form_state->setRebuild();
  }

  /**
   * Callback for both ajax-enabled buttons.
   *
   * Selects and returns the fieldset with the filters in it.
   */
  public function filtersFieldsetCallback(array &$form, FormStateInterface $form_state) {
    return $form['foo']['filters_fieldset'];
  }

  ...

}

Now when i click the add more button in the options form it Results in:

call_user_func_array() expects parameter 1 to be a valid callback, class 'Drupal\views_ui\Form\Ajax\Display' does not have a method 'addFilterEntry'

So I tried to specify it like:

'#submit' => [
    [$this, 'addFilterEntry'],
],

which actually lets call_user_func try to call 'addFilterEntry' on my class and i get

The specified #ajax callback is empty or not callable.

makes sense, now when I also change the ajax callback to

'#ajax' => [
   'callback' => [$this, 'filtersFieldsetCallback'],

I cant open the options form anymore resulting in a 5xx response

InvalidArgumentException: Recursion detected in Symfony\Component\HttpFoundation\JsonResponse->setData() (line 169 of /srv/www/htdocs/foo.dev/vendor/symfony/http-foundation/JsonResponse.php).

Drupal\Core\Ajax\AjaxResponseAttachmentsProcessor->processAttachments() (Line: 62)
Drupal\Core\EventSubscriber\AjaxResponseSubscriber->onResponse()
call_user_func() (Line: 142)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch() (Line: 191)
Symfony\Component\HttpKernel\HttpKernel->filterResponse() (Line: 179)
Symfony\Component\HttpKernel\HttpKernel->handleRaw() (Line: 80)
Symfony\Component\HttpKernel\HttpKernel->handle() (Line: 58)
Drupal\Core\StackMiddleware\Session->handle() (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle() (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle() (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle() (Line: 23)
Stack\StackedHttpKernel->handle() (Line: 708)
Drupal\Core\DrupalKernel->handle() (Line: 19)

i have a feeling that the difference is that the options form itself is already loaded with ajax but I have no clue how i can solve this or where to find example code

Answer 1

The plugin class is not a form class. The method buildOptionsForm is called by the parent form to get additional form elements. Callbacks referencing $this will reference an instance of the form class, not the plugin class.

You can only define static plugin callbacks

public static function filtersFieldsetCallback(array &$form, FormStateInterface $form_state) {
  return $form['foo']['filters_fieldset'];
}

referenced by the form element:

'#ajax' => [
  'callback' => [static::class, 'filtersFieldsetCallback'],

This is true for most option forms defined in plugins. Specific to this Views plugin is that form caching is disabled, so we can't use $form_state to store data between requests, only within the request. So try to count the fields in the submitted user input:

  // Gather the number of filters in the form already.
  $num_filters = $form_state->get('num_filters');

  if ($num_filters === NULL) {
    // Count the filter fields submitted. If none, start with one filter
    $input = $form_state->getUserInput();
    if (isset($input['foo']['filters_fieldset']['filter'])) {
      $num_filters = count($input['foo']['filters_fieldset']['filter']);
    }
    else {
      $num_filters = 1;          
    }
    $form_state->set('num_filters', $num_filters);
  }