Render login Form

Question

I would like to call the user login form in my theme but I can't.

In Drupal 7 I did this.

$elements = drupal_get_form("user_login"); 
$form = drupal_render($elements);    
echo utf8_decode($form);

How I can do this with Drupal 8?

I tried this.

Drupal::formBuilder()->getForm(Drupal\user\Form\UserLoginForm::class) 

How do I render this?

With the following code, I can show the login form, but I can't log in with it. What should I add to make it work?

$form = Drupal::formBuilder()->getForm(Drupal\user\Form\UserLoginForm::class) ; 
$render = Drupal::service('renderer');
$render->renderPlain($form); 

Answer 1

The code seems to be working fine. If it doesn't work for some reason, make sure that there is nothing else in the theme or modules that might interfere with this.

Here's how to provide a rendered login form through preprocess function. (This code would go to YOUR_THEME.theme file.)

function YOUR_THEME_preprocess_page(&$variables) {
  // You will most likely want to show and render the form for anonymous users.
  $variables['login_form'] = FALSE;
  if (!\Drupal::currentUser()->id()) {
    $form = Drupal::formBuilder()->getForm(Drupal\user\Form\UserLoginForm::class) ; 
    $render = Drupal::service('renderer');
    $variables['login_form'] = $render->renderPlain($form);
  }
}

Then in the page.html.twig template, you can render it (and use it) with the following code.

{{ login_form }}

Answer 2

You should use \Drupal::service('renderer')->renderRoot() instead of drupal_render() which is deprecated in Drupal 8, e.g.

$output = \Drupal::service('renderer')->renderRoot($form);

Answer 3

In D8 you create render Arrays in Controllers (extends Drupal\Core\Controller\ControllerBase). For your need you could do it like with the following code.

$fb = $this->formBuilder();
return $fb->getForm("Drupal\user\Form\UserLoginForm");