ViewsFormMainForm::validateForm

public ViewsFormMainForm::validateForm(array &$form, FormStateInterface $form_state)

public function validateForm(array &$form, FormStateInterface $form_state) {
  $view = $form_state->getBuildInfo()['args'][0];

  // Call the validation method on every field handler that has it.
  foreach ($view->field as $field) {
    if (method_exists($field, 'viewsFormValidate')) {
      $field->viewsFormValidate($form, $form_state);
    }
  }

  // Call the validate method on every area handler that has it.
  foreach (array('header', 'footer') as $area) {
    foreach ($view->{$area} as $area_handler) {
      if (method_exists($area_handler, 'viewsFormValidate')) {
        $area_handler->viewsFormValidate($form, $form_state);
      }
    }
  }
}