Tutorials - Drupal

This is due to file/folder permission. so drupal cant write twig tempory files.

This is due to trusted host configuration of the serveur. It can produce when you change the domain name or 'trusted_host_patterns'. To resolve the probleme, add your new domain to the DRUPAL_ROOT/sites/SITE_FOLDER/settings.php (Ex: sites/defaults/settings.php)

To set configuration at the module installation

Exemple:
$site_name = \Drupal::config('system.site')->get('name');
// Set the site name.
\Drupal::configFactory()->getEditable('system.site')->set('name', 'My site')->save();

You can do that using Symfony JsonResponse.

Exemple 1.
return new \Symfony\Component\HttpFoundation\JsonResponse($array);

As the solution depend on your error, first of all, you must find why drupal crash.

1. First thing is, You must check the serveur error log.
# tail -f /var/log/apache2/error.log

Exemple:

Here an exemple : Module name : mymodule

Here an example to get the current page path programmatically in Drupal 8

    $current_url = Url::fromRoute('<current>');
    $path = $current_url->toString();

Exemple : Field 'username'

Store data on session.

Example:

$session = new \Symfony\Component\HttpFoundation\Session\Session();
$session->set('var_name', $session->get('var_name',0) + 1);
drupal_set_message($session->get('var_name'));