How to pass query parameter in form submit?

Question

I have a form :

function buildForm(array $form, FormStateInterface $form_state) {
    $form['edit'] = array(
          '#type' => 'textfield',
    );
    $form['submit'] = array(
          '#type' => 'submit',
          '#value' => t('Go'),
          //'#markup' => "<div><a href='?word=1'>Go</a></div>",
        );
    return $form;
}

Now I want is; when I submit form,$form_state->getValue('edit'); should get appended as a query parameter in form route.

Let's say my form route is:

mymodule.admin_page:
  path: '/mypage'
  defaults:
    _form: '\Drupal\mymodule\Form\myform'

And when I hit submit button of form, the route should get changed to /mypage?word=$form_state->getValue('edit').

I tried below approach, but it is throwing error:

Created 1 more route with a parameter:

mymodule.word:
  path: '/mypage/{word}'
  defaults:
    _controller: '\Drupal\mymodule\Controller\AdminController::myfunction'

And in my form submit function,

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

    $data = $form_state->getValue('edit');
    $url = Url::fromRoute('mymodule.word',['word'=>$data]);
    $form_state->setRedirectUrl($url);
   }

But when I hit submit button, it is giving me error,

Uncaught PHP Exception Symfony\Component\Routing\Exception\MissingMandatoryParametersException: "Some mandatory parameters are missing"

Answer 1

Stick with your original route definition:

mymodule.word:
  path: '/mypage'
  defaults:
    _controller: '\Drupal\mymodule\Controller\AdminController::myfunction'

Then set your submit handler to this:

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

  $data = $form_state->getValue('edit');
  $url = Url::fromRoute('mymodule.word', [], ['query' => ['word' => $data]]);
  $form_state->setRedirectUrl($url);
}