ArticleSettingsForm.php

<?php

namespace Drupal\article_queue\Form;

use Drupal\Core\Form\ConfigFormBase;
use Drupal\Core\Form\FormStateInterface;

/**
 * Class ArticleSettingsForm.
 */
class ArticleSettingsForm extends ConfigFormBase {

  /**
   * {@inheritdoc}
   */
  protected function getEditableConfigNames() {
    return [
      'article_queue.articlesettings',
    ];
  }

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

  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $config = $this->config('article_queue.articlesettings');
    $form['site_url'] = [
      '#type' => 'textfield',
      '#title' => $this->t('Site URL'),
      '#description' => $this->t('Enter Connector Site URL'),
      '#maxlength' => 64,
      '#size' => 64,
      '#default_value' => $config->get('site_url'),
    ];
    $form['username'] = [
      '#type' => 'textfield',
      '#title' => $this->t('Username'),
      '#description' => $this->t('Enter Connector Site User Name'),
      '#maxlength' => 64,
      '#size' => 64,
      '#default_value' => $config->get('username'),
    ];
    $form['password'] = [
      '#type' => 'textfield',
      '#title' => $this->t('Password'),
      '#description' => $this->t('Enter Connector Site Password'),
      '#maxlength' => 64,
      '#size' => 64,
      '#default_value' => $config->get('password'),
    ];
    return parent::buildForm($form, $form_state);
  }

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

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

    $this->config('article_queue.articlesettings')
      ->set('site_url', $form_state->getValue('site_url'))
      ->set('username', $form_state->getValue('username'))
      ->set('password', $form_state->getValue('password'))
      ->save();
  }
}