Joomla Developer Manual

Dependency Injection

Introduction¶

Dependency injection (DI) is a software development technique that provides a class with its dependencies from outside, instead of creating them internally. It improves code flexibility, maintainability and testability. However, it is difficult to understand!

There is an explanation of DI and Dependency Injection Containers in the Joomla Framework DI documentation. There is also an Overview of its use.

The explanations in the Dependency Injection section of the Joomla! Programmers Documentation are not so easy to understand!

Examples¶

If your aim is to get going with building an extension the following examples taken from the Joomla core extensions may help.

The dependency injection code is located in services/provider.php but the exact location of that file is dependent on the extension type.

Component Example¶

The full path to the services/provider.php file is administrator/components/com_example/services/provider.php. This example is com_tags, which does not use categories. If your component uses categories take a look at the services/provider.php code for com_content. You will need several Category related statements.

<?php

/**
 * @package     Joomla.Administrator
 * @subpackage  com_tags
 *
 * @copyright   (C) 2018 Open Source Matters, Inc. <https://www.joomla.org>
 * @license     GNU General Public License version 2 or later; see LICENSE.txt
 */

\defined('_JEXEC') or die;

use Joomla\CMS\Component\Router\RouterFactoryInterface;
use Joomla\CMS\Dispatcher\ComponentDispatcherFactoryInterface;
use Joomla\CMS\Extension\ComponentInterface;
use Joomla\CMS\Extension\Service\Provider\ComponentDispatcherFactory;
use Joomla\CMS\Extension\Service\Provider\MVCFactory;
use Joomla\CMS\Extension\Service\Provider\RouterFactory;
use Joomla\CMS\MVC\Factory\MVCFactoryInterface;
use Joomla\Component\Tags\Administrator\Extension\TagsComponent;
use Joomla\DI\Container;
use Joomla\DI\ServiceProviderInterface;

/**
 * The tags service provider.
 *
 * @since  4.0.0
 */
return new class () implements ServiceProviderInterface {
    /**
     * Registers the service provider with a DI container.
     *
     * @param   Container  $container  The DI container.
     *
     * @return  void
     *
     * @since   4.0.0
     */
    public function register(Container $container)
    {
        $container->registerServiceProvider(new MVCFactory('\\Joomla\\Component\\Tags'));
        $container->registerServiceProvider(new ComponentDispatcherFactory('\\Joomla\\Component\\Tags'));
        $container->registerServiceProvider(new RouterFactory('\\Joomla\\Component\\Tags'));
        $container->set(
            ComponentInterface::class,
            function (Container $container) {
                $component = new TagsComponent($container->get(ComponentDispatcherFactoryInterface::class));
                $component->setMVCFactory($container->get(MVCFactoryInterface::class));
                $component->setRouterFactory($container->get(RouterFactoryInterface::class));

                return $component;
            }
        );
    }
};

Module Example¶

This is the Version module that shows the Joomla Version in the title bar of Administrator pages. The code is in administrator/modules/mod_version/services/provider.php

<?php

/**
 * @package     Joomla.Administrator
 * @subpackage  mod_version
 *
 * @copyright   (C) 2024 Open Source Matters, Inc. <https://www.joomla.org>
 * @license     GNU General Public License version 2 or later; see LICENSE.txt
 */

\defined('_JEXEC') or die;

use Joomla\CMS\Extension\Service\Provider\HelperFactory;
use Joomla\CMS\Extension\Service\Provider\Module;
use Joomla\CMS\Extension\Service\Provider\ModuleDispatcherFactory;
use Joomla\DI\Container;
use Joomla\DI\ServiceProviderInterface;

return new class () implements ServiceProviderInterface {
    /**
     * Registers the service provider with a DI container.
     *
     * @param   Container  $container  The DI container.
     *
     * @return  void
     *
     * @since   5.1.0
     */
    public function register(Container $container)
    {
        $container->registerServiceProvider(new ModuleDispatcherFactory('\\Joomla\\Module\\Version'));
        $container->registerServiceProvider(new HelperFactory('\\Joomla\\Module\\Version\\Administrator\\Helper'));

        $container->registerServiceProvider(new Module());
    }
};

Plugin Example¶

This is the plugin that provides contact information in content pages. The code is located in plugins/content/contact/services/provider.php

<?php

/**
 * @package     Joomla.Plugin
 * @subpackage  Content.contact
 *
 * @copyright   (C) 2022 Open Source Matters, Inc. <https://www.joomla.org>
 * @license     GNU General Public License version 2 or later; see LICENSE.txt
 */

\defined('_JEXEC') or die;

use Joomla\CMS\Extension\PluginInterface;
use Joomla\CMS\Factory;
use Joomla\CMS\Plugin\PluginHelper;
use Joomla\Database\DatabaseInterface;
use Joomla\DI\Container;
use Joomla\DI\ServiceProviderInterface;
use Joomla\Event\DispatcherInterface;
use Joomla\Plugin\Content\Contact\Extension\Contact;

return new class () implements ServiceProviderInterface {
    /**
     * Registers the service provider with a DI container.
     *
     * @param   Container  $container  The DI container.
     *
     * @return  void
     *
     * @since   4.3.0
     */
    public function register(Container $container)
    {
        $container->set(
            PluginInterface::class,
            function (Container $container) {
                $plugin     = new Contact(
                    $container->get(DispatcherInterface::class),
                    (array) PluginHelper::getPlugin('content', 'contact')
                );
                $plugin->setApplication(Factory::getApplication());
                $plugin->setDatabase($container->get(DatabaseInterface::class));

                return $plugin;
            }
        );
    }
};

Introduction
Examples