ASP.NET Web API Dependency Injection

Question

I would like to know if it is possible to do dependency injection (custom constructor) in a ASP.NET Web API without the use of third party libraries such as Unity or StructureMap and without Entity Framework.

What I would like to achieve is have a controller with a constructor such as:

public Controller(IDatabaseConnector connector) { ... }

I know for MVC you can make a custom ControllerFactory by inheriting from DefaultControllerFactory and then overriding the GetControllerInstance function. So I am sure there is an alternative for Web API.

Read up on IDependencyResolver for web api. Make sure it is for Web API as MVC has its own with the same name. — Nkosi
– Nkosi, Commented May 22, 2017 at 23:10
I ended up inheriting from IHttpControllerActivator and that did the trick for me. — Tyrone
– Tyrone, Commented May 22, 2017 at 23:23
When i was trying out asp core it had dependency injection in their sample page msdn.microsoft.com/en-us/magazine/mt703433.aspx — David Lee
– David Lee, Commented May 22, 2017 at 23:25
Dependency Injection doesn't require a DI Container at all. Hand-wiring your Dependency in the Composition Root is a common practice called Pure DI. As you already noticed, you need to implement a custom IHttpControllerActivator for this. — Steven
– Steven, Commented May 23, 2017 at 9:34

Francesco Bonizzi · Accepted Answer · 2017-05-23 13:35:22Z

4

At first you should define your own IHttpControllerActivator:

public class CustomControllerActivator : IHttpControllerActivator
{
    public IHttpController Create(
        HttpRequestMessage request,
        HttpControllerDescriptor controllerDescriptor,
        Type controllerType)
    {
        // Your logic to return an IHttpController
        // You can use a DI Container or you custom logic
    }
}

Then you should replace the default activator in the Global.asax:

protected void Application_Start()
{
    // ...

    GlobalConfiguration.Configuration.Services.Replace(
        typeof(IHttpControllerActivator),
        new CustomControllerActivator());
}

Now you can use your rich Controller constructor:

public class UserController
{
    public UserController(
        IMapper mapper,
        ILogger logger,
        IUsersRepository usersRepository)
    {
        // ...
    }

    // ...
}

answered May 23, 2017 at 13:35

Francesco Bonizzi

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1 Comment

Tyrone Over a year ago

I already did this as you could see in my comment on my post, but still thanks for the help! +1

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