class AreaPluginBase

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;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function usesGroupBy() {
        return FALSE;
    }
    
    /**
     * {@inheritdoc}
     */
    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'] = [
            'default' => FALSE,
        ];
        return $options;
    }
    
    /**
     * {@inheritdoc}
     */
    public function adminSummary() {
        return $this->adminLabel();
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        parent::buildOptionsForm($form, $form_state);
        if ($form_state->get('type') != 'empty') {
            $form['empty'] = [
                '#type' => 'checkbox',
                '#title' => $this->t('Display even if view has no result'),
                '#default_value' => isset($this->options['empty']) ? $this->options['empty'] : 0,
            ];
        }
    }
    
    /**
     * 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);
    
    /**
     * Does that area have nothing to show.
     *
     * This method should be overridden by more complex handlers where the output
     * is not static and maybe itself be empty if it's rendered.
     *
     * @return bool
     *   Return TRUE if the area is empty, else FALSE.
     */
    public function isEmpty() {
        return empty($this->options['empty']);
    }

}