SinglePageAttachment.php

<?php

namespace Drupal\dc_search\Plugin\views\display;

use Drupal\Core\Form\FormStateInterface;
use Drupal\views\Plugin\views\display\Attachment;
use Drupal\views\ViewExecutable;

/**
 * The plugin that handles a single-page attachment display.
 *
 * @ingroup views_display_plugins
 * @see \Drupal\views\Plugin\views\display\Attachment
 *
 * @ViewsDisplay(
 *   id = "dc_single_page_attachment",
 *   title = @Translation("Single page attachment"),
 *   help = @Translation("Attachments added to other displays to achieve multiple views in the same view."),
 *   theme = "views_view",
 *   contextual_links_locations = {""}
 * )
 */
class SinglePageAttachment extends Attachment {

  /**
   * {@inheritdoc}
   */
  protected function defineOptions() {
    $options = parent::defineOptions();

    $options['display_on_page'] = ['default' => '0'];

    return $options;
  }

  /**
   * Provide the summary for attachment options in the views UI.
   *
   * This output is returned as an array.
   */
  public function optionsSummary(&$categories, &$options) {
    // It is very important to call the parent function here:
    parent::optionsSummary($categories, $options);

    $options['display_on_page'] = array(
      'category' => 'attachment',
      'title' => $this->t('Display on page'),
      'value' => empty($this->getOption('display_on_page')) ? $this->t('every page') : $this->getOption('display_on_page'),
    );
  }

  /**
   * Provide the default form for setting options.
   */
  public function buildOptionsForm(&$form, FormStateInterface $form_state) {
    // It is very important to call the parent function here:
    parent::buildOptionsForm($form, $form_state);

    switch ($form_state->get('section')) {
      case 'display_on_page':
        $form['#title'] .= $this->t('Display on selected page');
        $form['display_on_page'] = [
          '#type' => 'number',
          '#title' => $this->t('Page'),
          '#description' => $this->t('Enter the page number on which the display should be attached. Leave empty or set to 0 for all pages'),
          '#default_value' => $this->getOption('display_on_page'),
          '#min' => 0,
        ];
        break;
    }
  }

  /**
   * Perform any necessary changes to the form values prior to storage.
   * There is no need for this function to actually store the data.
   */
  public function submitOptionsForm(&$form, FormStateInterface $form_state) {
    // It is very important to call the parent function here:
    parent::submitOptionsForm($form, $form_state);
    $section = $form_state->get('section');
    switch ($section) {
      case 'display_on_page':
        $this->setOption($section, $form_state->getValue($section));
        break;
    }
  }

  /**
   * {@inheritdoc}
   */
  public function attachTo(ViewExecutable $view, $display_id, array &$build) {
    if (!$this->view->displayHandlers->get($display_id)->usesPager() || empty($this->getOption('display_on_page'))) {
      // No pager used or attach to every page.
      parent::attachTo($view, $display_id, $build);
      return;
    }

    $pager = $this->view->pager;
    if ($pager && ($this->getOption('display_on_page') - 1) === $pager->current_page) {
      // Attach to current page.
      parent::attachTo($view, $display_id, $build);
      return;
    }
  }

}