How to display a form in controller method

Question

I have a form defined in mymodule/src/Form/myForm.php

namespace Drupal\mymodule\Form;

use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;

class myForm extends FormBase {

/**
 * Specify the form ID.
 */
public function getFormId() {
  return 'mymodule_myform';
}

  /**
   * Build the actual form.
   */
  public function buildForm(array $form, FormStateInterface $form_state) {

    // Form API code here...

Originally, this routing worked fine and the form displayed at the correct path:

mymodule.single_tab:
  path: '/node/{node}/edit/performance'
  defaults:
    _form: '\Drupal\mymodule\Form\myForm'
    _title: 'Add performance'

Then I needed to add a custom access check, restricting to a specific content type:

mymodule.single_tab:
  path: '/node/{node}/edit/performance'
  defaults:
    _title: 'Add performance'
    _controller: '\Drupal\mymodule\Controller\mymoduleController::content'
  requirements:
    _custom_access: '\Drupal\mymodule\Controller\mymoduleController::checkAccess'

The access check works fine. Now I think I have to display my form in the controller:

namespace Drupal\mymodule\Controller;

use Drupal\Core\Controller\ControllerBase;
use Drupal\Core\Form\FormBuilderInterface;
use Drupal\Core\Access\AccessResult;
use Drupal\node\Entity\Node;

/**
 * Controller for Add Performance single tab.
 */
class mymoduleController extends ControllerBase {

  /**
   * Returns the add single performance form.
   */
  public function content() {
    $form = $this->formBuilder->getForm('Drupal\mymodule\Form\myForm');
        return [
          '#type' => 'markup',
          '#markup' => $form
        ];
  }

This fails to display the form, and I get:

Call to a member function getForm() on null

I tried defining my form builder class inside the controller instead, but same result. What am I doing wrong?

Answer 1

Thanks to Kevin's comment, I realised that I can just return the form AND still use the custom access check reference to a controller method:

mymodule.single_tab:
  path: '/node/{node}/edit/performance'
  defaults:
    _form: '\Drupal\add_performance\Form\myForm'
    _title: 'Add performance'
  requirements:
    _custom_access: '\Drupal\add_performance\Controller\mymoduleController::checkAccess'
  options: