A service locator is an object that knows how to provide all sorts of services (or components) that an application might need. Within a service locator, each component exists as only a single instance, uniquely identified by an ID. You use the ID to retrieve a component from the service locator.
In Yii, a service locator is simply an instance of yii\di\ServiceLocator or a child class.
The most commonly used service locator in Yii is the application object, which can be accessed through \Yii::$app. The services it provides are called application components, such as the request, response, and urlManager components. You may configure these components, or even replace them with your own implementations, easily through functionality provided by the service locator.
Besides the application object, each module object is also a service locator. Modules implement tree traversal.
To use a service locator, the first step is to register components with it. A component can be registered via yii\di\ServiceLocator::set(). The following code shows different ways of registering components :
use yii\di\ServiceLocator;
use yii\caching\FileCache;
$locator = new ServiceLocator;
// register "cache" using a class name that can be used to create a component
$locator->set('cache', 'yii\caching\ApcCache');
// register "db" using a configuration array that can be used to create a component
$locator->set('db', [
'class' => 'yii\db\Connection',
'dsn' => 'mysql:host=localhost;dbname=demo',
'username' => 'root',
'password' => '',
]);
// register "search" using an anonymous function that builds a component
$locator->set('search', function () {
return new app\components\SolrService;
});
// register "pageCache" using a component
$locator->set('pageCache', new FileCache);
Once a component has been registered, you can access it using its ID, in one of the two following ways :
$cache = $locator->get('cache');
// or alternatively
$cache = $locator->cache;
