DrupalTutorial/themes/bootstrap/docs/plugins/Form.md

@BootstrapForm

• Create a plugin
• Rebuild the cache

---

Create a plugin

We'll use SearchBlockForm implemented by this base theme as an example of how to remove #input_group_button from search_block_form.

Replace all following instances of THEMENAME with the actual machine name of your sub-theme.

Create a file at ./themes/THEMENAME/src/Plugin/Form/SearchBlockForm.php with the following contents:

<?php

namespace Drupal\THEMENAME\Plugin\Form;

use Drupal\bootstrap\Plugin\Form\SearchBlockForm as BootstrapSearchBlockForm;
use Drupal\bootstrap\Utility\Element;
use Drupal\Core\Form\FormStateInterface;

/**
 * Implements hook_form_FORM_ID_alter().
 *
 * @ingroup plugins_form
 *
 * @BootstrapForm("search_block_form")
 */
class SearchBlockForm extends BootstrapSearchBlockForm {

  /**
   * {@inheritdoc}
   */
  public function alterForm(array &$form, FormStateInterface $form_state, $form_id = NULL) {
    // Call the parent method from the base theme, if applicable (which it is
    // in this case because Bootstrap actually implements this alter).
    parent::alterForm($form, $form_state, $form_id);

    // Disable #input_group_button the normal way:
    $form['keys']['#input_group_button'] = FALSE;
  }

  /**
   * {@inheritdoc}
   */
  public function alterFormElement(Element $form, FormStateInterface $form_state, $form_id = NULL) {
    // This method is the same as above, except the the $form argument passed is
    // an instance of \Drupal\bootstrap\Utility\Element for easier manipulation.
    // Using this method is preferable and considered "Best Practice".
    //
    // Disable #input_group_button using the $form Element object:
    // $form->keys->setProperty('input_group_button', FALSE);.
  }

  /**
   * {@inheritdoc}
   */
  public static function submitForm(array &$form, FormStateInterface $form_state) {
    // This method is automatically called when the form is submitted.
  }

  /**
   * {@inheritdoc}
   */
  public static function submitFormElement(Element $form, FormStateInterface $form_state) {
    // This method is the same as above, except the the $form argument passed is
    // an instance of \Drupal\bootstrap\Utility\Element for easier manipulation.
    // Using this method is preferable and considered "Best Practice".
  }

  /**
   * {@inheritdoc}
   */
  public static function validateForm(array &$form, FormStateInterface $form_state) {
    // This method is automatically called when the form is validated.
  }

  /**
   * {@inheritdoc}
   */
  public static function validateFormElement(Element $form, FormStateInterface $form_state) {
    // This method is the same as above, except the the $form argument passed is
    // an instance of \Drupal\bootstrap\Utility\Element for easier manipulation.
    // Using this method is preferable and considered "Best Practice".
  }

}
?>

Rebuild the cache

Once you have saved, you must rebuild your cache for this new plugin to be discovered. This must happen anytime you make a change to the actual file name or the information inside the @BootstrapForm annotation.

To rebuild your cache, navigate to admin/config/development/performance and click the Clear all caches button. Or if you prefer, run drush cr from the command line.

Voilà! After this, you should have a fully functional @BootstrapForm plugin!