Ninject constructor argument

Question

I have this interface:

public interface IUserProfileService
{
    // stuff
}

Implemented by:

public class UserProfileService : IUserProfileService
{
    private readonly string m_userName;

    public UserProfileService(string userName)
    {
        m_userName = userName;
    }
}

I need this injected into a controller like this:

public class ProfilesController : BaseController
{
    private readonly IUserProfileService m_profileService;

    public ProfilesController(IUserProfileService profileService)
    {
        m_profileService = profileService;
    }
}

I don't know how I can register this interface and its implementation into Ninject container so that userName param is passed in when the Ninject inits an instance of this service.

Any ideas how I can achieve this?

I'm in general agreement with what Mike described. For a bit more detail and explanation I'd recommend reading Ruben Bartelink's answer here: http://stackoverflow.com/questions/2227548/creating-an-instance-using-ninject-with-additional-parameters-in-the-constructor. This is a very thorough answer for what you're looking to achieve. — Khepri, Jun 12 '11 at 16:33

score 5 · Answer 1 · answered Jun 14 '11 at 12:30

The technical ninject answer is to use constructor arguments like so:

Bind<IUserProfileService>().To<UserProfileService>().WithConstructorArgument("userName", "karl");

Of course you need to figure out where "karl" comes from. It really depends on your app. Maybe its a web app and it's on the HttpContex? I don't know. If it gets rather complicated then you might want to write a IProvider rather than doing a regular binding.

score 3 · Accepted Answer · answered Jun 12 '11 at 16:27

3

One alternative is to inject a factory and create your dependency using Create(string userName).

public class UserProfileServiceFactory
{
    public IUserProfileService Create(string userName)
    {
        return new UserProfileService(userName);
    }
}

It might seem off to have to create another class but the benefits mostly comes when UserProfileService takes in additional dependencies.

answered Jun 12 '11 at 16:27

Mike

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Would the ProfilesController constructor then take a UserProfileServiceFactory and a userName? – JDawg Jan 23 '15 at 22:07

Steven · Answer 3 · 2011-06-14T12:31:08.833

The trick is to not inject the username in that class. You call this class a service so it would probably work transparantly with multiple users. I see two solutions:

Inject an abstraction into the service that represents the current user:

public class UserProfileService : IUserProfileService
{
    private readonly IPrincipal currentUser;

    public UserProfileService(IPrincipal currentUser)
    {
        this.currentUser = currentUser;
    }

    void IUserProfileService.SomeOperation()
    {
        var user = this.currentUser;

        // Do some nice stuff with user
    }
}

Create an implementation that is specific to the technology you are working with, for instance:

public class AspNetUserProfileService : IUserProfileService
{
    public AspNetUserProfileService()
    {
    }

    void IUserProfileService.SomeOperation()
    {
        var user = this.CurrentUser;

        // Do some nice stuff with user
    }

    private IPrincipal CurrentUser
    {
        get { return HttpContext.Current.User; }
    }
}

If you can, go with option one.

On option one, assuming IPrincipal's concrete constructor takes a userName argument, how does this option help? — JDawg, Jan 23 '15 at 21:55

Ninject constructor argument

3 Answers3