Issue #3268008 by RenatoG: Create the formValidate and formSubmit to SettingsForm

    return $form;

  }

  /**

   * Validate the maxlength field.

   */

  public function validateForm(array &$form, FormStateInterface $form_state) {

    parent::validateForm($form, $form_state);

    // Get the maxlength_block_class_field field.

    $maxlength_block_class_field = $form_state->getValue('maxlength_block_class_field');

    // Verify if is a positive value.

    if ($maxlength_block_class_field < 1) {

      $form_state->setErrorByName('maxlength_block_class_field', $this->t('The maxlength should be an positive value'));

    }

  }

  /**

   * {@inheritdoc}

   */

  public function submitForm(array &$form, FormStateInterface $form_state) {

    // Get the maxlength_block_class_field field.

    $maxlength_block_class_field = $form_state->getValue('maxlength_block_class_field');

    // Get the config object.

    $config = $this->config('block_class.settings');

    // Set the value.

    $config->set('maxlength_block_class_field', $maxlength_block_class_field);

    // Save that.

    $config->save();

    parent::submitForm($form, $form_state);

  }

}