A list and a detail view

Could you, please, tell me how to do this:

https:///categories/ - a list of categories.

https:///categories/?id=1 - details about each category.

I've done:

class CategoriesController extends Controller 
{
    public function actionIndex($id=null)
    {
        if ($id) 
        {
           $category = Category::findOne($id);
           return $this->render("detail", compact("category"));
        } else
        {
           $categories = Category::find()->all();
            return $this->render("index", compact("categories"));        
        }
    }
}

The problem is that if I'm not mistaken in Yii world there exists a tradition to call a view after an action id. But here I have two views.

Could you tell how should it be done? If this code is ugly, how to do it better?

When using pretty URL's you need to make ID as part of path, so your second URL should be https://example.com/categories/1. Then you would map it into different controller actions. Please see documentation