.NET MVC - where to use dependency injection?

Question

I'm currently injecting dependencies into controllers using a IoC container (Castle). This is possible because you need to create a custom controller factory which enables the dependency injection.

What are other examples of dependency injection? At which point in an MVC application would you use it, and where does a 'factory' come into play?

If you use Castle, I would suggest that code.google.com/p/sutekishop, personally, I feel it's a very good example to follow regarding how to use IOC — J.W.
– J.W., Commented Feb 12, 2011 at 19:54
I'm looking at Sutekishop but cannot download the latest source code? — Ropstah
– Ropstah, Commented Feb 13, 2011 at 13:41

LukLed · Accepted Answer · 2011-02-12 20:10:12Z

3

I am using Ninject. At my project:

Service layer objects are injected into controllers (using constructor).
Repositories are injected into service layer objects (using constructor).
ObjectContext is injected into repositories (using constructor).
web.config setting are encapsulated into a class, which implements IAppSettings interface, which is then injected into service layer.
NinjectActionInvoker is injected as IActionInvoker. It takes care of injecting services into ActionFilters.
I have my own implementation of IPrincipal interface, which is injected into service layer, instead of referring to HttpContext.Current.User.

Example using Ninject:

public class UserService : GenericService<User>, IUserService
{
    public ISettingService SettingService { get; set; }
    public ICTEmailSender CTEmailSender { get; set; }
    public ICTSettings CTSettings { get; set; }
    public ICTPrincipal User { get; set; }
}

Ninject rules:

Bind<ICTPrincipal>().ToMethod(c => (ICTPrincipal)HttpContext.Current.User).OnlyIf(a => HttpContext.Current.User is ICTPrincipal);
Bind<ICTEmailSender>().To<CTEmailSender>();
Bind<ICTSettings>().To<CTSettings>();

Not only service is injected into controller, but parts of service are injected into it. It makes service more testable. I am sure it can be easily ported into Castle.

edited Feb 12, 2011 at 20:10

answered Feb 12, 2011 at 17:33

LukLed

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15 Comments

Steven Over a year ago

In other words: Dependency Injection all the way ;-)

J.W. Over a year ago

Pretty interesting, any example that we can follow

Ropstah Over a year ago

Yes this should port easily. I was a bit off track focusing on a factory that needed to be applied, however this is not the case. You can also inject methods and other objects without a factory.

Ropstah Over a year ago

Is it typical for different components (like: Controllers, Services, Repositories) to be 'installed' using separate configurations (e.g. IWindsorInstaller in Windsor)? I'm deducting from documentation that this is indeed the case. However it's also allowing for only one 'binding' per dependency. What if two components depend on the same object, where (in which installer) would you configure or install this binding?

LukLed Over a year ago

@Ropstah: I am not an expert in Windsor, but from what I see in documentation, you should have it in installer related to this object's class. If this object is Repository, you should place it in RepositoryInstaller.

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