moodle-hooks-api

Moodle Hooks API

Overview

Moodle 4.4 introduced a typed Hooks API (core\hook\manager) replacing the unmaintainable jungle of magic callback functions like <plugin>_extend_navigation, <plugin>_before_http_headers, <plugin>_extend_settings_navigation, etc. Hooks are real classes with typed payloads, dispatched through \core\di::get(\core\hook\manager::class). Plugins register interest via db/hooks.php.

When to Use

• Adding cross-cutting behavior triggered by core (navigation, page output, user login, course events) without monkey-patching
• Migrating a plugin off legacy magic callbacks (deprecated 4.4+, will be removed)
• Authoring a hook class in core or in a plugin that other plugins can listen to
• Writing tests for hook listeners

Skip when: the event you care about is a \core\event\* (Events 2 API — different system, used for audit/logging). Hooks are for modifying behavior; Events are for reacting to facts.

Core concepts

Concept	Where it lives	Purpose
Hook class	classes/hook/<name>.php	Typed payload, optional setters for listeners to mutate
Listener registration	db/hooks.php	Maps hook class -> callback (Class::method) + priority
Dispatcher call	Core or plugin code	\core\di::get(\core\hook\manager::class)->dispatch(new \plugin\hook\thing(...));
Listener method	Any class	Static or instance method taking the hook instance

Listening to a core hook

db/hooks.php:

<?php
defined('MOODLE_INTERNAL') || die();

$callbacks = [
    [
        'hook'     => \core\hook\output\before_standard_top_of_body_html_generation::class,
        'callback' => \local_example\hook_listener::class . '::inject_banner',
        'priority' => 100, // higher runs first
    ],
];

classes/hook_listener.php:

<?php
namespace local_example;

use core\hook\output\before_standard_top_of_body_html_generation as hook;

class hook_listener {
    public static function inject_banner(hook $hook): void {
        global $USER;
        if (isguestuser() || !isloggedin()) {
            return;
        }
        $hook->add_html('<div class="alert alert-info">Hello, ' . s($USER->firstname) . '</div>');
    }
}

After adding or changing db/hooks.php, purge caches: php admin/cli/purge_caches.php.

Authoring your own hook

classes/hook/before_widget_render.php:

<?php
namespace local_example\hook;

use core\hook\described_hook_interface;
use core\hook\stoppable_event_interface;

class before_widget_render implements described_hook_interface, stoppable_event_interface {
    private bool $stopped = false;
    private string $html = '';

    public function __construct(public readonly int $widgetid, public readonly \context $context) {}

    public static function get_hook_description(): string {
        return 'Dispatched before a widget renders. Listeners may append HTML or veto rendering.';
    }

    public static function get_hook_tags(): array {
        return ['output', 'widget'];
    }

    public function add_html(string $html): void { $this->html .= $html; }
    public function get_html(): string { return $this->html; }

    public function stop(): void { $this->stopped = true; }
    public function isPropagationStopped(): bool { return $this->stopped; }
}

Dispatch:

$hook = new \local_example\hook\before_widget_render($widgetid, $context);
\core\di::get(\core\hook\manager::class)->dispatch($hook);
if ($hook->isPropagationStopped()) {
    return ''; // veto
}
echo $hook->get_html();

Migrating magic callbacks

Legacy callback	Replacement hook
<plugin>_extend_navigation	\core\hook\navigation\primary_extend (4.5+) — check core for current name
<plugin>_before_http_headers	\core\hook\output\before_http_headers
<plugin>_before_standard_top_of_body_html	\core\hook\output\before_standard_top_of_body_html_generation
<plugin>_before_footer	\core\hook\output\before_footer_html_generation
<plugin>_after_config	\core\hook\after_config
<plugin>_extend_settings_navigation	check \core\hook\navigation\* for current name

Migration steps:

1. Search for legacy callbacks: grep -rn "function.*_extend_navigation\|_before_http_headers\|_after_config" .
2. For each, find the matching hook class in lib/classes/hook/ of your Moodle install.
3. Create db/hooks.php mapping; move the callback body into a listener class.
4. Delete the legacy function from lib.php.
5. Bump version.php, purge caches, run tests.

Testing hook listeners

<?php
namespace local_example;

defined('MOODLE_INTERNAL') || die();

final class hook_listener_test extends \advanced_testcase {
    /** @covers \local_example\hook_listener::inject_banner */
    public function test_banner_injected_for_logged_in_user(): void {
        $this->resetAfterTest();
        $this->setUser($this->getDataGenerator()->create_user());

        $hook = new \core\hook\output\before_standard_top_of_body_html_generation();
        \core\di::get(\core\hook\manager::class)->dispatch($hook);

        $this->assertStringContainsString('Hello,', $hook->get_output());
    }

    public function test_skipped_for_guest(): void {
        $this->resetAfterTest();
        $this->setGuestUser();

        $hook = new \core\hook\output\before_standard_top_of_body_html_generation();
        \core\di::get(\core\hook\manager::class)->dispatch($hook);

        $this->assertStringNotContainsString('Hello,', $hook->get_output());
    }
}

CLI: list registered hooks

php admin/cli/hooks_list.php          # all hooks + listeners
php admin/cli/hooks_list.php --hook=core\\hook\\output\\before_http_headers

Gotchas

• Purge caches after any db/hooks.php change. Listener registration is cached.
• Priority is a hint — order between equal priorities is undefined. Don't rely on it for correctness.
• Stoppable hooks: only implement stoppable_event_interface if vetoing is meaningful. Most output hooks are not stoppable.
• Don't dispatch hooks from constructors or setUp() — they can have side effects.
• DI container: always resolve manager via \core\di::get(...). Don't new it.
• Backporting: pre-4.4 plugins still need legacy callbacks. Either keep both with a version check, or drop pre-4.4 support and bump requires in version.php.

Checklist

• db/hooks.php exists with correct hook class FQCN
• Listener class is autoloadable (under classes/ with PSR-4)
• Caches purged after edit
• Tests cover both the action and the no-op branch
• Legacy callback removed (or version-gated) after migration
• version.php bumped