How to call a controller method whose name is in a variable?

Question

Yii

Yii2. The bottom line is that I want to get the names of the controllers from the database and call one method from them. I try:

public function actionIndex()
{
    $plugin = 'FilesController';
    $data['files'] = $plugin::thumbnail();
    return $this->render('index', ['data' => $data]);
}

I get: Class 'FilesController' not found .
Although:

public function actionIndex()
{
    $data['files'] = FilesController::thumbnail();
    return $this->render('index', ['data' => $data]);
}

works. What am I doing wrong?
upd: Of course, I solved the problem by specifying the class name along with the namespace, but I feel that this is not the true way

$plugin = 'app\modules\cabinet\controllers\FilesController';
    $data['files'] = $plugin::thumbnail();

Answer 1

Why not do so?

$plugin = __NAMESPACE__ . '/FilesController';
$data['files'] = $plugin::thumbnail();

Or

$plugin = __NAMESPACE__ . '/FilesController';
$data['files'] = call_user_func([$plugin, 'thumbnail']);