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The plugin class has not changed in any significant manner apart from the fact that it can now be namespaced and have any name you please as we learned in the previous two sections. It still extends from \Joomla\CMS\Plugin\CMSPlugin or one of its subclasses.

The biggest difference is that since Joomla 4.0 you can implement the \Joomla\Event\SubscriberInterface in your plugin class to handle modern events instead of registering plugin event callbacks, as we already discussed.

The other big change starting with Joomla 4.2 is that you no longer need to declare an $app property to magically get access to the Joomla application object or a $db property to magically get access to the database driver object. Instead, you need to set up these features through your service provider.

Accessing the Joomla application object

Modify your provider's return line to read something like the following:

// Create the plugin
$plugin = Example($subject, $config);
// Push the application object
$plugin->setApplication(\Joomla\CMS\Factory::getApplication());

return $plugin;

In your plugin's code you can now get the Joomla application object by doing

$app = $this->getApplication();

Accessing the Joomla database driver object

Accessing the Joomla database driver object is slightly more complicated.

First of all, your plugin class must have the \Joomla\Database\DatabaseAwareInterface in its implements list and use the \Joomla\Database\DatabaseAwareTrait. For example:

class Example extends \Joomla\CMS\Plugin\CMSPlugin
implements \Joomla\Database\DatabaseAwareInterface
{
    use \Joomla\Database\DatabaseAwareTrait;

    // The rest of the plugin class goes here.
}

Your service provider must have the following line before the return $plugin; line:

$plugin->setDatabase($container->get('DatabaseDriver'));

Inside your plugin's class you can now access the database driver object like this:

$db = $this->getDatabase();