class InputRequired

class InputRequired extends ExposedFormPluginBase {
    protected function defineOptions() {
        $options = parent::defineOptions();
        $options['text_input_required'] = [
            'default' => $this->t('Select any filter and click on Apply to see results'),
        ];
        $options['text_input_required_format'] = [
            'default' => NULL,
        ];
        return $options;
    }
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        parent::buildOptionsForm($form, $form_state);
        $form['text_input_required'] = [
            '#type' => 'text_format',
            '#title' => $this->t('Text on demand'),
            '#description' => $this->t('Text to display instead of results until the user selects and applies an exposed filter.'),
            '#default_value' => $this->options['text_input_required'],
            '#format' => isset($this->options['text_input_required_format']) ? $this->options['text_input_required_format'] : filter_default_format(),
            '#editor' => FALSE,
        ];
    }
    public function submitOptionsForm(&$form, FormStateInterface $form_state) {
        $exposed_form_options = $form_state->getValue('exposed_form_options');
        $form_state->setValue([
            'exposed_form_options',
            'text_input_required_format',
        ], $exposed_form_options['text_input_required']['format']);
        $form_state->setValue([
            'exposed_form_options',
            'text_input_required',
        ], $exposed_form_options['text_input_required']['value']);
        parent::submitOptionsForm($form, $form_state);
    }
    protected function exposedFilterApplied() {
        static $cache = NULL;
        if (!isset($cache)) {
            $view = $this->view;
            if (is_array($view->filter) && count($view->filter)) {
                foreach ($view->filter as $filter) {
                    if ($filter->isExposed()) {
                        $identifier = $filter->options['expose']['identifier'];
                        if (isset($view->getExposedInput()[$identifier])) {
                            $cache = TRUE;
                            return $cache;
                        }
                    }
                }
            }
            $cache = FALSE;
        }
        return $cache;
    }
    public function preRender($values) {
        // Display the "text on demand" if needed. This is a site builder-defined
        // text to display instead of results until the user selects and applies
        // an exposed filter.
        if (!$this->exposedFilterApplied()) {
            $options = [
                'id' => 'area',
                'table' => 'views',
                'field' => 'area',
                'label' => '',
                'relationship' => 'none',
                'group_type' => 'group',
                // We need to set the "Display even if view has no result" option to
                // TRUE as the input required exposed form plugin will always force an
                // empty result if no exposed filters are applied.
'empty' => TRUE,
                'content' => [
                    // @see \Drupal\views\Plugin\views\area\Text::render()
'value' => $this->options['text_input_required'],
                    'format' => $this->options['text_input_required_format'],
                ],
            ];
            $handler = Views::handlerManager('area')->getHandler($options);
            $handler->init($this->view, $this->displayHandler, $options);
            $this->displayHandler->handlers['empty'] = [
                'area' => $handler,
            ];
            // Override the existing empty result message (if applicable).
            $this->displayHandler
                ->setOption('empty', [
                'text' => $options,
            ]);
        }
    }
    public function query() {
        if (!$this->exposedFilterApplied()) {
            // We return with no query; this will force the empty text.
            $this->view->built = TRUE;
            $this->view->executed = TRUE;
            $this->view->result = [];
        }
        else {
            parent::query();
        }
    }

}