paragraphs_views/src/Plugin/Field/FieldFormatter/ViewsFormatter.php

<?php

namespace Drupal\paragraphs_views\Plugin\Field\FieldFormatter;

use Drupal\Component\Utility\Html;
use Drupal\Core\Field\FieldItemInterface;
use Drupal\Core\Field\FieldItemListInterface;
use Drupal\Core\Field\FormatterBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\views\Element\View;
use Drupal\views\Views;

/**
 * Plugin implementation of the 'paragraphs_views_formatter' formatter.
 *
 * @FieldFormatter(
 *   id = "paragraphs_views_formatter",
 *   label = @Translation("Views formatter"),
 *   field_types = {
 *     "entity_reference"
 *   }
 * )
 */
class ViewsFormatter extends FormatterBase {
  const DISPLAY = 'display';

  /**
   * {@inheritdoc}
   */
  public static function defaultSettings() {
    return array(
      'display' => NULL,
    ) + parent::defaultSettings();
  }

  /**
   * {@inheritdoc}
   */
  public function settingsForm(array $form, FormStateInterface $form_state) {
    $elements = [];
    $elements['display'] = array(
      '#type' => 'textfield',
      '#title' => t('Name of View display'),
      '#default_value' => $this->getSetting('display'),
      '#description' => t('The machine name of the display to use for when executing the view'),
      '#required' => FALSE
    );

    return $elements + parent::settingsForm($form, $form_state);
  }

  /**
   * {@inheritdoc}
   */
  public function settingsSummary() {
    $summary = [];
    $display = $this->getSetting('display');
    $summary[] = t('Display: @display', array('@display' => $display ?: t('(default)')));

    return $summary;
  }

  /**
   * {@inheritdoc}
   */
  public function viewElements(FieldItemListInterface $items, $langcode) {
    $elements = [];
    $display = $this->getSetting(static::DISPLAY) ?? 'default';

    /**
     * @var \Drupal\Core\Field\Plugin\Field\FieldType\EntityReferenceItem $item
     */
    foreach ($items as $delta => $item) {
      $target = $item->getValue()['target_id'];
      $view = \Drupal\views\Entity\View::load($target);
      $exec = $view->getExecutable();
      $elements[$delta] = ['view' => $exec->preview($display)];
    }

    $elements['#cache'] = [
      'max-age' => 0,
    ];
    return $elements;
  }

  /**
   * Generate the output appropriate for one field item.
   *
   * @param \Drupal\Core\Field\FieldItemInterface $item
   *   One field item.
   *
   * @return string
   *   The textual output generated.
   */
  protected function viewValue(FieldItemInterface $item) {
    // The text value has no text format assigned to it, so the user input
    // should equal the output, including newlines.
    return nl2br(Html::escape($item->value));
  }

}