class PluginTypeExampleController

class PluginTypeExampleController extends ControllerBase {
  
  /**
   * The sandwich plugin manager.
   *
   * We use this to get all of the sandwich plugins.
   *
   * @var \Drupal\plugin_type_example\SandwichPluginManager
   */
  protected $sandwichManager;
  
  /**
   * Constructor.
   *
   * @param \Drupal\plugin_type_example\SandwichPluginManager $sandwich_manager
   *   The sandwich plugin manager service. We're injecting this service so that
   *   we can use it to access the sandwich plugins.
   */
  public function __construct(SandwichPluginManager $sandwich_manager) {
    $this->sandwichManager = $sandwich_manager;
  }
  
  /**
   * Displays a page with an overview of our plugin type and plugins.
   *
   * Lists all the Sandwich plugin definitions by using methods on the
   * \Drupal\plugin_type_example\SandwichPluginManager class. Lists out the
   * description for each plugin found by invoking methods defined on the
   * plugins themselves. You can find the plugins we have defined in the
   * \Drupal\plugin_type_example\Plugin\Sandwich namespace.
   *
   * @return array
   *   Render API array with content for the page at
   *   /examples/plugin_type_example.
   */
  public function description() {
    $build = [];
    $build['intro'] = [
      '#markup' => $this->t("This page lists the sandwich plugins we've created. The sandwich plugin type is defined in Drupal\\plugin_type_example\\SandwichPluginManager. The various plugins are defined in the Drupal\\plugin_type_example\\Plugin\\Sandwich namespace."),
    ];
    // Get the list of all the sandwich plugins defined on the system from the
    // plugin manager. Note that at this point, what we have is *definitions* of
    // plugins, not the plugins themselves.
    $sandwich_plugin_definitions = $this->sandwichManager
      ->getDefinitions();
    // Let's output a list of the plugin definitions we now have.
    $items = [];
    foreach ($sandwich_plugin_definitions as $sandwich_plugin_definition) {
      // Here we use various properties from the plugin definition. These values
      // are defined in the annotation at the top of the plugin class: see
      // \Drupal\plugin_type_example\Plugin\Sandwich\ExampleHamSandwich.
      $items[] = $this->t("@id (calories: @calories, description: @description )", [
        '@id' => $sandwich_plugin_definition['id'],
        '@calories' => $sandwich_plugin_definition['calories'],
        '@description' => $sandwich_plugin_definition['description'],
      ]);
    }
    // Add our list to the render array.
    $build['plugin_definitions'] = [
      '#theme' => 'item_list',
      '#title' => 'Sandwich plugin definitions',
      '#items' => $items,
    ];
    // If we want just a single plugin definition, we can use getDefinition().
    // This requires us to know the ID of the plugin we want. This is set in the
    // annotation on the plugin class: see
    // \Drupal\plugin_type_example\Plugin\Sandwich\ExampleHamSandwich.
    $ham_sandwich_plugin_definition = $this->sandwichManager
      ->getDefinition('meatball_sandwich');
    // To get an instance of a plugin, we call createInstance() on the plugin
    // manager, passing the ID of the plugin we want to load. Let's output a
    // list of the plugins by loading an instance of each plugin definition and
    // collecting the description from each.
    $items = [];
    // The array of plugin definitions is keyed by plugin id, so we can just use
    // that to load our plugin instances.
    foreach ($sandwich_plugin_definitions as $plugin_id => $sandwich_plugin_definition) {
      // We now have a plugin instance. From here on it can be treated just as
      // any other object; have its properties examined, methods called, etc.
      $plugin = $this->sandwichManager
        ->createInstance($plugin_id, [
        'of' => 'configuration values',
      ]);
      $items[] = $plugin->description();
    }
    $build['plugins'] = [
      '#theme' => 'item_list',
      '#title' => 'Sandwich plugins',
      '#items' => $items,
    ];
    return $build;
  }
  
  /**
   * {@inheritdoc}
   *
   * Override the parent method so that we can inject our sandwich plugin
   * manager service into the controller.
   *
   * For more about how dependency injection works read
   * https://www.drupal.org/node/2133171
   *
   * @see container
   */
  public static function create(ContainerInterface $container) {
    // Inject the plugin.manager.sandwich service that represents our plugin
    // manager as defined in the plugin_type_example.services.yml file.
    return new static($container->get('plugin.manager.sandwich'));
  }

}