Redirect to Different URl on validation errors in form builder

Question

I am using drupal 8 fapi and i have user case as below

I have a form on https://example.com/landing-page and I submit the form and there are validation errors .the page should reload as https://example.com/landing-page#lead-form.

Is there any hack we can implement?

I came with logic

if validation has error set form redirect page to example.com/landing-page#lead-form

if($form_state->getErrors() ) {
  $response = new TrustedRedirectResponse('example.com/landing-page#lead-form');
  $form_state->setResponse($response);
}

some how its not working.

Is there any way we can change the url to example.com/landing-page#lead-form and show the validation error at same time .

Answer 1

You can use like

For Internal:

global $base_url;
$response = new TrustedRedirectResponse($base_url.'/landing-page#lead-form');
// You can use any one of these below to show error message.
$form_state->setError($element, $message);
$form_state->setErrorByName($element, $message);
$form_state->setResponse($response);

For External: Use full link

$response = new TrustedRedirectResponse('https://facebook.com');
// You can use any one of these below to show error message.
$form_state->setError($element, $message);
$form_state->setErrorByName($element, $message);
$form_state->setResponse($response);

Answer 2

You can use EnforcedResponseException to terminate form processing and redirect:

$response = new RedirectResponse(Url::fromRoute('user.login', [], ['absolute' => TRUE])->toString());
throw new \Drupal\Core\Form\EnforcedResponseException($response);

For external urls use TrustedRedirectResponse not RedirectResponse:

$response = TrustedRedirectResponse('http://www.google.com');
throw new \Drupal\Core\Form\EnforcedResponseException($response);