Plugin discovery is the process by which Drupal finds plugins of a given type. A discovery method must be set for every plugin type (explained in the plugin manager documentation).
The discovery component of plugins implements a DiscoveryInterface that defines the methods any discovery class must have.
<?php
/**
* @file
* Contains \Drupal\Component\Plugin\Discovery\DiscoveryInterface.
*/
namespace Drupal\Component\Plugin\Discovery;
/**
* Defines the plugin discovery interface.
*/
interface DiscoveryInterface {
/**
* Gets a specific plugin definition.
*
* @param string $plugin_id
* A plugin id.
*
* @return array
* A plugin definition.
*/
public function getPluginDefinition($plugin_id);
/**
* Gets the definition of all plugins for this type.
*
* @return array
* An array of configuration definitions.
*/
public function getPluginDefinitions();
}
?>There are three different core discovery types.
- StaticDiscovery
StaticDiscovery allows for direct registration of plugins within the discovery class itself. A protected variable (
$definitions) in the class holds all plugin definitions that are registered with it through the public methodsetDefinition(). Any plugin defined through this method can then be invoked as outlined in the plugin manager documentation. - HookDiscovery
The HookDiscovery class allows Drupal's
hook_component_info()/hook_component_info_alter()pattern to be used for plugin discovery. With this discovery, the plugin manager will invoke info hooks to retrieve a list of available plugins. - AnnotatedClassDiscovery
The AnnotatedClassDiscovery class uses name of the annotations that contains the plugin definition, e.g.,
@Plugin,@EntityType, in plugin docblocks to discover plugins, minimizing memory usage during the discovery phase. The AnnotatedClassDiscovery class takes two arguments in its constructor,$ownerand$type. The$owneris the module that owns the plugins type, and$typeis the plugin type. The AnnotatedClassDiscovery class scans PSR-0 classes inside Plugin folders to find plugins.