abstract class AreaPluginBase

DisplayPluginBase.php in drupal/core/modules/views/lib/Drupal/views/Plugin/views/display/DisplayPluginBase.php

Contains Drupal\views\Plugin\views\display\DisplayPluginBase.

ListingEmpty.php in drupal/core/modules/node/lib/Drupal/node/Plugin/views/area/ListingEmpty.php

Contains \Drupal\node\Plugin\views\area\ListingEmpty.

TestExample.php in drupal/core/modules/views/tests/views_test_data/lib/Drupal/views_test_data/Plugin/views/area/TestExample.php

Definition of Drupal\views_test_data\Plugin\views\area\TestExample

abstract class AreaPluginBase extends HandlerBase {

  /**
   * The type of this area handler, i.e. 'header', 'footer', or 'empty'.
   *
   * @var string
   */
  public $areaType;

  /**
   * Overrides Drupal\views\Plugin\views\HandlerBase::init().
   *
   * Make sure that no result area handlers are set to be shown when the result
   * is empty.
   */
  public function init(ViewExecutable $view, DisplayPluginBase $display, array &$options = NULL) {
    parent::init($view, $display, $options);
    if ($this->areaType == 'empty') {
      $this->options['empty'] = TRUE;
    }
  }
  protected function defineOptions() {
    $options = parent::defineOptions();
    $this->definition['field'] = !empty($this->definition['field']) ? $this->definition['field'] : '';
    $label = !empty($this->definition['label']) ? $this->definition['label'] : $this->definition['field'];
    $options['admin_label']['default'] = $label;
    $options['empty'] = array(
      'default' => FALSE,
      'bool' => TRUE,
    );
    return $options;
  }

  /**
   * Provide extra data to the administration form
   */
  public function adminSummary() {
    return $this
      ->adminLabel();
  }

  /**
   * Default options form that provides the label widget that all fields
   * should have.
   */
  public function buildOptionsForm(&$form, &$form_state) {
    parent::buildOptionsForm($form, $form_state);
    if ($form_state['type'] != 'empty') {
      $form['empty'] = array(
        '#type' => 'checkbox',
        '#title' => t('Display even if view has no result'),
        '#default_value' => isset($this->options['empty']) ? $this->options['empty'] : 0,
      );
    }
  }

  /**
   * Don't run a query
   */
  public function query() {
  }

  /**
   * Performs any operations needed before full rendering.
   *
   * @param array $results
   *  The results of the view.
   */
  public function preRender(array $results) {
  }

  /**
   * Render the area.
   *
   * @param bool $empty
   *   (optional) Indicator if view result is empty or not. Defaults to FALSE.
   *
   * @return array
   *   In any case we need a valid Drupal render array to return.
   */
  public abstract function render($empty = FALSE);

  /**
   * Area handlers shouldn't have groupby.
   */
  public function usesGroupBy() {
    return FALSE;
  }

}