Show form message only on initial load, but not after submit

Question

I'm often using Drupal::messenger() to show status/warning messages before I submit the form. But those messages are usually counter-intuitive once the form has been submitted. How can I add a message to a form that is only rendered before the form has been submitted.

My typical code looks like this:

function buildForm() {
  /**
   * ...build form...
   */
  $showWarning = $this->doSomeChecks();

  /**
   * tried to use isSubmitted() to prevent the message after submitting, but does not work
   */
  if ($showWarning  && !$form_state->isSubmitted()) {
    $this->messenger()->addWarning('Some info you should know before submitting this form.');
  }
}

function submitForm(array &$form, FormStateInterface $form_state) {
  /**
   * ...do stuff...
   */
  $this->messenger()->addMessage('Successfully done something');

  /**
   * tried to use deleteByType() to remove message from buildForm after submitting, but does not work
   */
  $this->messenger()->deleteByType($this->messenger()::TYPE_WARNING);
}

I know I could use $form_state->setRedirect($customPage) in submitForm(), but I don't want the overhead of creating a new page just to hide a simple warning message.

Is there no simple way to show a message only once on the initial form load, but not after submit?

Answer 1

Try

if (empty($form_state->getUserInput())) {
  $this->messenger()->addWarning('Some info you should know before submitting this form.');  
}

See the discussions here: Avoid repetitive API calling in form rebuild while submitting

Answer 2

This is my current version working for my simple usecase. Since buildForm() is triggered multiple times during a single submit request, the combined check empty($form_state->getUserInput()) && !$form_state->isRebuilding() allowed me to detect if the form was initially loaded/not submitted yet.

class MyConfirmForm extends ContentEntityConfirmFormBase {

  public function getQuestion() {
    return $this->t('Do you want to do stuff?');
  }

  function buildForm(array $form, FormStateInterface $form_state) {
    $form = parent::buildForm($form, $form_state);

    $showWarning = $this->doSomeChecks();

    if ($showWarning && empty($form_state->getUserInput()) && !$form_state->isRebuilding()) {
      $this->messenger()->addWarning('Some info you should know before submitting this form.');
    }

    return $form;
  }

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

    $result = $this->doStuff();

    if ($result) {
      $this->messenger()->addMessage('Successfully done something');
      $form_state->setRebuild(TRUE);
    }
  }
}

I'm leaving the question open though, because @4k4 indicated in comments above that using $form_state->setRebuild() inside submitForm() is not a good practice.

Answer 3

You can try

$request = \Drupal::request()->server;
$http_referer = $request->get('HTTP_REFERER');
$showWarning = TRUE;
if ($http_referer) {
  $host = $request->get('HTTP_HOST');
  $request_scheme = $request->get('REQUEST_SCHEME');
  $current_url = str_replace($request_scheme . '://' . $host, '', $http_referer);
  $url_object = \Drupal::service('path.validator')->getUrlIfValid($current_url);
  $route_name = $url_object->getRouteName();
  if ($route_name === 'custom.router') {
    $showWarning = FALSE;
  }
}

if ($showWarning &&  $this->doSomeChecks()) {
  this->messenger()->addWarning('Some info you should know before submitting this form.');
}