I have a simple custom form that works until I try to add a custom parameter for my module called "forms_admin".

These are the contents of my forms_admin.routing.yml

  path: 'admin/config/system/forms/{arg1}'
    _form: '\Drupal\forms_admin\Form\FormSettings'
    _title: 'Forms Settings'
    _permission: 'access content'

This is a relevant part of my FormSettings.php file (Currently do not have any custom Validation or Submit actions)

public function buildForm(array $form, FormStateInterface $form_state, $arg1 = NULL) {
    $form['title'] = array(
      '#type' => 'textfield',
      '#title' => t('Title'),
      '#required' => TRUE,

    $form['submit'] = array(
      '#type' => 'submit',
      '#value' => t('Submit'),

return $form;

And my third file is: forms_admin.links.menu.yml

  title: Forms
  route_name: forms_admin.settings
  parent: system.admin_config_system
  description: 'Forms settings'
  weight: 0

The moment that I add {arg1} to my forms_admin.routing.yml and , $arg1 = NULL to my FormSettings.php file, I am unable to acces the website.

I receive a white page with the error that states:

The website encountered an unexpected error. Please try again later.

After removing arg1 from my two files and going to the Recent Log messages, this is the error I receive:

Symfony\Component\Routing\Exception\MissingMandatoryParametersException: Some mandatory parameters are missing ("arg1") to generate a URL for route "forms_admin.settings". in Drupal\Core\Routing\UrlGenerator->doGenerate() (line 182 of /var/www/test_site/docroot/core/lib/Drupal/Core/Routing/UrlGenerator.php).

I have tried changing arg1 to other names, not making $arg1 = NULL, etc. and I receive an error every time.

What am I missing?

  • 1
    It looks good to me - the parameter is named the same and is optional. The error indicates something's trying to generate a URL from the route without a parameter (which obviously can't work). I'm not sure the error's coming directly from a mistake in the code you've posted (it just manifests when you have a required parameter). If you have for example a menu link tied to the route you should provide a default parameter so it can generate the URL IIUC. See optional parameters from the routing docs.
    – Andy
    Jul 27, 2018 at 11:03
  • @Andy The menu link was the issue! Thank you for catching that! How do I modify it to provide a default parameter? Jul 27, 2018 at 16:16
  • It's not the link itself that you need to modify, it's the route: see the link in my previous comment and look under optional parameters. For example in ban.routing.yml there are two routes with parameters, but only ban.admin_page specifies a default for its parameter.
    – Andy
    Jul 28, 2018 at 9:58

1 Answer 1


The problem is that your FormSettings class is not the controller in this case. It's the controller method which is where the routing system expects $arg_1.

I think you need to define your own controller which accepts the request and passes the argument to the form. Extending the core Drupal\Core\Controller\FormController class is probably the simplest way forward.

  • I don't think you need a custom controller to pass on arguments. See eg. ban.delete in ban.routing.yml and Drupal\ban\Form\BanDelete::buildForm().
    – Andy
    Jul 27, 2018 at 10:52
  • I stand corrected. How odd that your code doesn't work, then. Jul 27, 2018 at 10:57
  • 1
    Is there a reference to "forms_admin.settings" anywhere else? Seems like it's the default (without arg) that's being objected to. Maybe try adding a default entry for it in routing.yml? Jul 27, 2018 at 11:01
  • Just posted the same, didn't notice your reply - that's my guess, yeah.
    – Andy
    Jul 27, 2018 at 11:04
  • Thank you for all of your comments and thoughts! The issue ended up being in my .links.menu.yml file. Jul 27, 2018 at 16:16

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