Question

Scenario:

An MVC3 app that uses constructor injection to provide services for a given controller:

public class HomeController : BaseController
{
    private readonly IArticleService _articleService;

    public HomeController(IArticleService articleService)
    {
        _articleService = articleService;
    }

    public ActionResult Index()
    {
        // do stuff with services
        return View()
    }
}

Intention:

I have a UserService that fetches user principal data from Active Directory that I want usable from all my Controllers, from the base controller.

I have tried to inject this service into my BaseController like this:

public class BaseController : Controller
{
    private readonly IUserService _userService;

    public BaseController(IUserService userService)
    {
        _userService = userService;
    }
}

All by itself it looks fine, but now the constructor in my HomeController is off, as it needs a : base() initializer. The trouble is, the base initializer is not parameterless due the UserService injection.

public HomeController(IArticleService articleService) : base(IUserService userService)

The code above results in syntax errors.

Question(s):

How do I properly inject a service into my BaseController and initialize it from the child Controller classes (ex. HomeController)?

Answer 1

The user service interface must be included in the child controllers’ constructor arguments in addition to the base initializer arguments. Like this:

public class HomeController : BaseController
{
    private readonly IArticleService _articleService;

    public HomeController(IArticleService articleService, IUserService userService) : base(userService)
    {
        _articleService = articleService;
    }

    public ActionResult Index()
    {
        // do stuff with services
        return View()
    }
}

Note: in order to do anything with the base controller’s UserService from the inherited controllers, change the access modified from private to protected.