Drupal 8 \Drupal calls should be avoided in classes, use | | dependency injection instead

Question

I used Drupal 8 and written a module. in my form page I called.

\Drupal::service('library.discovery')->clearCachedDefinitions();
$cache = \Drupal::cache('discovery');
      $cache->delete('block_plugins');

It's worked, but I always see the warning.

\Drupal calls should be avoided in classes, use | | dependency injection instead

I have the similar with File::load(), too. I used:

use Drupal\file\Entity\file;
class BXBlock extends BlockBase {
public function build() {
...
$file = File::load($value);
...
}
}

Anybody can help me, please? Thanks so much.

Answer 1

You can check how the dependency injection works in general in this documentation. https://www.drupal.org/docs/8/api/services-and-dependency-injection/dependency-injection-for-a-form

The parts that you need are:

Use statement -

 use Symfony\Component\DependencyInjection\ContainerInterface;

Class property - here we are going to store the whole \Drupal::service('current_user') object.

 protected $account;

The __construct magic method. This is called upon instantiating the class. The dependency injection bit here is providing all the data required in a later stage as input.

function __construct(AccountInterface $account) {

Built in method that has a dependency injection create(ContainerInterface $container)

return new static(
  // Load the service required to construct this class.
  $container->get('current_user')
);

Eventually we are using the whole construction like that:

$uid = $this->account->id();

where $this->account is the same like \Drupal::service('current_user');