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In Back-Office, migrated pages are powered by Symfony. The powerful Symfony Event Dispatcher has been chosen to replace, in the long term, hooks. However, in order to preserve backward compatibility, both systems coexist.
It is important that modules which subscribe to a hook are correctly notified no matter where the hook is dispatched from, be it in legacy code or modern code.
In legacy code, hooks are dispatched using Hook::exec().
In Symfony-powered code, two services work together to achieve this:
Hook class and Symfony.First, on setup, LegacyHookSubscriber will retrieve all legacy hooks using Hook::getHooks().
Then it will create as many event subscriptions as there are hooks, following a naming convention based on database IDs.
For example, if module with id_module 267 has subscribed to hook with id_hook 82, LegacyHookSubscriber will create a subscription call_82_267.
In Symfony-powered pages, to dispatch hook one must use the HookDispatcher:
$this->hookDispatcher->dispatchWithParameters("actionModifyForm", ['form_builder' => $formBuilder]);
The HookDispatcher will act as standard dispatcher and call the eligible event listeners and subscribers, including LegacyHookSubscriber.
Using a dedicated magic method __call(), the LegacyHookSubscriber will parse the called method (ex: call_82_267) to retrieve the appropriate hook and module (using their respective IDs) and trigger the related Hook::exec() call with the appropriate parameters.
When a hook is dispatched inside Symfony-powered controllers, HookDispatcher dispatches the hook similarly to a regular Symfony event; this event is being listened to by LegacyHookSubscriber who will then trigger the related Hook::exec() call.