Dependency Injection in Blocks

When to Use

Your block plugin needs access to Drupal services (database, config, entity manager, custom services).

Steps

Implement ContainerFactoryPluginInterface

use Drupal\Core\Plugin\ContainerFactoryPluginInterface;

class MyBlock extends BlockBase implements ContainerFactoryPluginInterface {

Add static create() method

public static function create(
  ContainerInterface $container,
  array $configuration,
  $plugin_id,
  $plugin_definition
) {
  return new static(
    $configuration,
    $plugin_id,
    $plugin_definition,
    $container->get('entity_type.manager'),
    $container->get('current_user')
  );
}

Add constructor with services

public function __construct(
  array $configuration,
  $plugin_id,
  $plugin_definition,
  protected EntityTypeManagerInterface $entityTypeManager,
  protected AccountInterface $currentUser,
) {
  parent::__construct($configuration, $plugin_id, $plugin_definition);
}

Use services in your methods

public function build() {
  $nodes = $this->entityTypeManager
    ->getStorage('node')
    ->loadByProperties(['type' => 'article']);
  // Build render array
}

Decision Points

At this step...	If...	Then...
Step 1 (interface)	Need any services	Always implement `ContainerFactoryPluginInterface`
Step 2 (create)	Many services	Use promoted properties (PHP 8.0+) for brevity
Step 3 (constructor)	Parent constructor needed	Always call `parent::__construct()` first
Step 4 (usage)	Service might not exist	Handle exceptions or check service exists

Pattern

Complete dependency injection example:

namespace Drupal\mymodule\Plugin\Block;

use Drupal\Core\Block\Attribute\Block;
use Drupal\Core\Block\BlockBase;
use Drupal\Core\Config\ConfigFactoryInterface;
use Drupal\Core\Entity\EntityTypeManagerInterface;
use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
use Drupal\Core\Session\AccountInterface;
use Drupal\Core\StringTranslation\TranslatableMarkup;
use Symfony\Component\DependencyInjection\ContainerInterface;

#[Block(
  id: "recent_articles",
  admin_label: new TranslatableMarkup("Recent Articles"),
)]
class RecentArticlesBlock extends BlockBase implements ContainerFactoryPluginInterface {

  public function __construct(
    array $configuration,
    $plugin_id,
    $plugin_definition,
    protected EntityTypeManagerInterface $entityTypeManager,
    protected AccountInterface $currentUser,
    protected ConfigFactoryInterface $configFactory,
  ) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
  }

  public static function create(
    ContainerInterface $container,
    array $configuration,
    $plugin_id,
    $plugin_definition
  ) {
    return new static(
      $configuration,
      $plugin_id,
      $plugin_definition,
      $container->get('entity_type.manager'),
      $container->get('current_user'),
      $container->get('config.factory')
    );
  }

  public function build() {
    $limit = $this->configFactory->get('mymodule.settings')->get('article_limit');

    $storage = $this->entityTypeManager->getStorage('node');
    $query = $storage->getQuery()
      ->condition('type', 'article')
      ->condition('status', 1)
      ->sort('created', 'DESC')
      ->range(0, $limit)
      ->accessCheck(TRUE);

    $nids = $query->execute();
    $nodes = $storage->loadMultiple($nids);

    $view_builder = $this->entityTypeManager->getViewBuilder('node');
    $build = [];
    foreach ($nodes as $node) {
      $build[] = $view_builder->view($node, 'teaser');
    }

    return $build;
  }

  public function getCacheTags() {
    return ['node_list'];
  }
}

Reference: core/modules/system/src/Plugin/Block/SystemBrandingBlock.php (lines 28-55), core/modules/user/src/Plugin/Block/UserLoginBlock.php (lines 41-80)

Common Mistakes

Using \Drupal::service() in block plugins → Use dependency injection; it's testable and follows best practices
Not implementing ContainerFactoryPluginInterface → Required for DI; without it services can't be injected
Wrong parameter order in __construct() → Must match parent: ($configuration, $plugin_id, $plugin_definition, ...services)
Forgetting to call parent::__construct() → BlockBase needs to initialize; always call parent
Injecting too many services → If you need >5 services, consider refactoring logic into a custom service
Not type-hinting services → Use interfaces (e.g., EntityTypeManagerInterface) not classes for flexibility