I have the following routes in module_name.routing.yml.

  path: 'module_name/usergroup/delete/{arg1}'
    _form: '\Drupal\module_name\Form\DeleteUserGroup'
    _title: 'Delete User group'
    _permission: 'access admin menus'

This is the code in module_name/src/Form/DeleteUserGroup.php.

namespace Drupal\module_name\Form;

use Drupal\Core\Form\ConfigFormBase;
use Drupal\Core\Form\FormStateInterface;

class DeleteUserGroup extends ConfigFormBase {

  public function getFormId() {
    return 'delete_user_group';
 * General form for switching all nodes from one user to another.
  public function buildForm(array $form, FormStateInterface $form_state,$product_code) {
  $form['_product'] = array(
        '#type' => 'value',
        '#value' => $product_code,);
//get the user group and username to display the confirmation message 
$result = db_query('select field_p_group_name_value from {content_type_usergroup} ctu'       
        . ' where vid=%d',$product_code);      
    while ($row = $result->fetchObject()) {
      $user_group = $row->field_p_group_name_value;

return confirm_form($form,t('Are you sure you want to delete "' .$user_group. '" User Group?'),
        isset($_GET['destination']) ? $_GET['destination'] : "function_name",t('This action cannot be undone.'),t('Delete'),t('Cancel'));

 * #submit callback for node_adoption_transfer_form().
  public function submitForm(array &$form, FormStateInterface $form_state) {
    $form_values = $form_state->getValues();
  //if ($form_state['values']['confirm']) {
    $param = $form_state->getValue('_product');
    drupal_set_message(t('Group ' .$param.' will get deleted.'));               
    db_query('DELETE FROM {content_type_usergroup} WHERE vid = %d', $param);
    //delete the users of the usergroup too
    db_query('DELETE FROM {usergroup_user_map} WHERE group_id=%d', $param);
    drupal_set_message(t('usergroup has been deleted.'));

  protected function getEditableConfigNames() {
    return "delete_user_group";


I am getting the following error:

DeleteUserGroup::buildForm() must be compatible with Drupal\Core\Form\FormInterface::buildForm(array $form, Drupal\Core\Form\FormStateInterface $form_state)


  • Can anyone explain how this equates when using the WebForm module? I have no module specifically for the form I have built using the module, so what would the point '_form' to within the routing.yml file ? – John Cogan Nov 6 '17 at 13:40

The parameter has to have the same name in routing.yml and build method. And when using parameters in forms you have to set a null value in the parameter list:

public function buildForm(array $form, FormStateInterface $form_state, $arg1 = NULL) {
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  • Ah yes! The additional parameters always have to be NULL to be compatible with Drupal\Core\Form\FormInterface::buildForm.💡 – leymannx Mar 17 at 22:13

First create a routing.yml file

  path: '/example_module/form/{arg}'
    _form: '\Drupal\example_module\Form\ExampleForm'
    _permission: 'access content'

Then create a .php file under folder structure /src/Form/ExampleForm.php .Then build a form

public function buildForm(array $form, FormStateInterface $form_state,$arg = NULL) {

             $form['example_note'] = array(
            '#type' => 'textarea',
            '#title' => t('Block contents'),
            '#description' => t('This text will appear in the example block.'),
            '#default_value' => $arg,
       $form['actions'] = ['#type' => 'actions'];
        $form['actions']['delete'] = array(
            '#type' => 'submit',
            '#value' => $this->t('Delete'),

return $form;
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