class Hook

Attribute for defining a class method as a hook implementation.

Hook implementations in classes need to be marked with this attribute, using one of the following techniques:

• On a method, use this attribute with the hook name:

  #[Hook('user_cancel')]
  public method userCancel(...)
  

• On a class, specifying the method name:

  #[Hook('user_cancel', method: 'userCancel')]
  class Hooks {
    method userCancel(...) {}
  }
  

• On a class with an __invoke method, which is taken to be the hook implementation:

  #[Hook('user_cancel')]
  class Hooks {
    method __invoke(...) {}
  }
  

Ordering hook implementations can be done by specifying the 'priority' on the attribute, or by manipulating the kernel listeners in service alter providers. See \Drupal\Core\Hook\HookOrder for details.

Classes that use this annotation on the class or on their methods are automatically registered as autowired services with the class name as the service ID. If autowire does not suffice, they can be registered manually as well.

Implementing a hook on behalf of another module can be done by by specifying the 'module' parameter in the attribute.

Multiple implementations

Multiple implementations are allowed on multiple axes:

• One method can implement multiple hooks by adding a Hook attribute for each method.
• One module can implement a particular hook multiple times in multiple classes, although see below for some exceptions. This allows, for example, adding hook_form_alter() implementations firing on other conditions than form ID without modifying any existing implementations.

The following hooks may not have multiple implementations by a single module:

• hook_library_build_info()
• hook_mail()
• hook_help()
• hook_node_update_index()

Procedural hooks

The following hooks can only have procedural hook implementations:

Legacy meta hooks:

• hook_hook_info()
• hook_module_implements_alter()

Install hooks:

• hook_cache_flush()
• hook_install()
• hook_module_preinstall()
• hook_module_preuninstall()
• hook_modules_installed()
• hook_modules_uninstalled()
• hook_post_update_NAME()
• hook_schema()
• hook_uninstall()
• hook_update_last_removed()
• hook_update_N()

Theme hooks:

• hook_preprocess_HOOK()
• hook_process_HOOK()

Backwards-compatibility

To allow hook implementations to work on older versions of Drupal as well, add both an attribute-based hook implementation and a procedural hook implementation, with the \Drupal\Core\Hook\Attribute\LegacyHook attribute on the procedural hook implementations.

See \Drupal\Core\Hook\Attribute\LegacyHook for additional information.

Hierarchy

• class \Drupal\Core\Hook\Attribute\Hook

Expanded class hierarchy of Hook

File

core/lib/Drupal/Core/Hook/Attribute/Hook.php, line 95

Namespace

class Hook {
    
    /**
     * Constructs a Hook attribute object.
     *
     * @param string $hook
     *   The short hook name, without the 'hook_' prefix.
     * @param string $method
     *   (optional) The method name. If this attribute is on a method, this
     *   parameter is not required. If this attribute is on a class and this
     *   parameter is omitted, the class must have an __invoke() method, which is
     *   taken as the hook implementation.
     * @param int|null $priority
     *   (optional) The priority of this implementation relative to other
     *   implementations of this hook. Hook implementations with higher priority
     *   are executed first. If omitted, the module order is used to order the
     *   hook implementations.
     * @param string|null $module
     *   (optional) The module this implementation is for. This allows one module to
     *   implement a hook on behalf of another module. Defaults to the module the
     *   implementation is in.
     */
    public function __construct(string $hook, string $method = '', ?int $priority = NULL, ?string $module = NULL) {
    }
    
    /**
     * Set the method the hook should apply to.
     *
     * @param string $method
     *   The method that the hook attribute applies to.
     *   This only needs to be set when the attribute is on the class.
     */
    public function setMethod(string $method) : static {
        $this->method = $method;
        return $this;
    }

}

Members