Symfony 4会议正在服务中

Question

I'm trying to use session variables in my custom service.

I already set add the following lines to services.yaml

MySession:
    class: App\Services\SessionTest
    arguments: ['@session', '@service_container']

And my SessionTest looks like this

namespace App\Services;

use Symfony\Component\HttpFoundation\Session\SessionInterface;
use Symfony\Component\HttpFoundation\Request;

class SessionTest
{
    public $session;

    public function __construct()
    {

    }
    public function index()
    {
        echo "<pre>";
        var_dump($this->session);
        echo "</pre>";
    }
}

And receive this error: Too few arguments to function App\Services\SessionTest::__construct(), 0 passed in /var/www/app.dev/src/Controller/OrdersController.php on line 33 and exactly 1 expected