materio-d8/web/modules/custom/materio_sapi/src/Form/MaterioSapiSearchForm.php

<?php

namespace Drupal\materio_sapi\Form;

use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;

/**
 * Class MaterioSapiSearchForm.
 */
class MaterioSapiSearchForm extends FormBase {


  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return 'materio_sapi_search_form';
  }

  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $form['search'] = [
      '#type' => 'textfield',
      // '#title' => $this->t('Search'),
      '#maxlength' => 64,
      '#size' => 25,
      '#weight' => '0',
      '#attributes' => [
        "placeholder" => $this->t('Search'),
      ],
      '#autocomplete_route_name' => 'materio_sapi.search_autocomplete',
    ];
    $form['submit'] = [
      '#type' => 'submit',
      '#value' => $this->t('Search'),
    ];

    return $form;
  }

  /**
   * {@inheritdoc}
   */
  public function validateForm(array &$form, FormStateInterface $form_state) {
    parent::validateForm($form, $form_state);
  }

  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    // Display result.
    foreach ($form_state->getValues() as $key => $value) {
      drupal_set_message($key . ': ' . $value);
    }

  }

}