How do I render a form?

Question

What is the alternative to drupal_get_form('user_login'). in Drupal 8?

I am using the following code in theme_name.theme, but it doesn't work.

// Include namespace for userLoginForm.
use \Drupal\Core\core\modules\user\src\Form;

function MYTHEMENAME_preprocess_page(&$variables) {
  $form = UserLoginForm::create();
} 

Answer 1

drupal_get_form() has been replaced by the form builder service, e.g.:

$form = \Drupal::formBuilder()->getForm(\Drupal\user\Form\UserLoginForm::class);

See the Change Record for more details.

Actually, don't - that change record is incorrect. It'll tell you to pass the form ID, when in fact you need to pass the class string.

Answer 2

You can create a form under form folder . And then you can call your form anywhere and pass the paramater as shown.

Drupal 7 : $form = drupal_get_form('form_id',$parameter);

Drupal 8 : $form = \Drupal::formBuilder()->getForm('Drupal\custom_module\Form\CustomModuleForm',$parameter);

Answer 3

There are two options to return(D8) or render(D7) a form. These are \Drupal::formBuilder()->getForm and Drupal::formBuilder()->buildForm. I use \Drupal::formBuilder()->getForm as below.

Use this if you are not passing a parameter:

$form = \Drupal::formBuilder()->getForm('\Drupal\example\Form\ExampleForm');
return $form;

Use this if you are passing a parameter:

$parameter = "your_parameter";
$form = \Drupal::formBuilder()->getForm('\Drupal\example\Form\ExampleForm', $parameter);
return $form;
//pass to formbuild function
public function buildForm(array $form, FormStateInterface $form_state, $parameter = NULL){//form code}

---

Drupal 7 Equivalent of the above:

$parameter = 'your_parameter';
$form = drupal_get_form('form_id', $parameter);
print drupal_render($form);
//pass to form function
function form_id ($form, &$form_state, $parameter){//form code}

Cheers. Let me know if it helps.

Answer 4

The documentation does allow an instance of the class as well. So

$formObj = new \Drupal\demo\Form\MyForm();
$form = \Drupal::formBuilder()->getForm($formObj);

is also correct.

Answer 5

Ok if all else fails here is a sneaky trick by setting a new form state object.

use Drupal\Core\Form\FormState;
...

$form_state = new FormState();
$form_state->set('name', $name);
$form_state->set('user', $user);
$render_array = \Drupal::formBuilder()->buildForm('\Drupal\mod\Form\MyForm', $form_state);
...
// Example render.
$response = new AjaxResponse();
// Show a dialog box.
$dialogText['#attached']['library'][] = 'core/drupal.dialog.ajax';
$response->addCommand(new OpenModalDialogCommand("Dialog Title", $render_array, ['width' => '300']));
return $response;

... then in your form method buildForm you can then...

 // Get form state.
 $name = $form_state->get('name');
 if (!empty($name)) {
    $form['name'] = [
      '#type' => 'item',
      '#markup' => $name,
    ];
  }

Answer 6

Assuming the below is your form class

namespace Drupal\demo\Form;
use \Drupal\Core\Form\FormBase;
class MyForm extends FormBase {
}

You have to create a new instance from your form class first, and pass it to formBuilder's getForm.

$form_obj = new \Drupal\demo\Form\MyForm();
$form = \Drupal::formBuilder()->getForm($form_obj);