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'));
    }

}