How to configure Web Api 2 to look for Controllers in a separate project? (just like I used to do in Web Api)

I used to place my controllers into a separate Class Library project in Mvc Web Api. I used to add the following line in my web api project's global.asax to look for controllers in the separate project:

ControllerBuilder.Current.DefaultNamespaces.Add("MyClassLibraryProject.Controllers");

I never had to do any other configuration, except for adding the above line. This has always worked fine for me.

However I am unable to use the above method to do the same in WebApi2. It just doesn't work. The WebApi2 project still tries to find the controllers in its own project's controllers folder.

-- Giving little summary update after 2 months (As I started bounty on this):

I have created a WebApiOne solution, it has 2 projects, the first one is WebApi project, and the second is a class library for controllers. If I add the reference to the controllers class library project into the WebApi project, all works as expected. i.e. if i go to http://mydevdomain.com/api/values i can see the correct output.

I have now create a second project called WebApiTwo, it has 2 projects, the first one is WebApi2 project, and the second is a class library for controllers. If I add the reference to the controllers class library project to the WebApi2 project, it doest NOT work as expected. i.e. if i go to http://mydevdomain.com/api/values i get "No type was found that matches the controller named 'values'."

for the first project i am not doing any custom settings at all, i do NOT have:

ControllerBuilder.Current.DefaultNamespaces.Add("MyClassLibraryProject.Controllers");

in my global.asax, and i have not implemented any custom solutions proposed by StrathWeb in two of his blog posts, as i think its not applicable any more; because all works just by adding the reference of the controller project to the WebApi project.

So i would expect all to work same for WebApi2 ... but its not. Has anyone really tried doing this in WebAPi2 ?

I have just confirmed that this works fine. Things to check:

References: Does your main Web API project reference the external class library?

Routing: Have you set up any routes that might interfere with the external controllers?

Protection Level: Are the controllers in the external library public?

Inheritance: Do the controllers in the external library inherit from ApiController?

Versioning: Are both your Web API project and class library using the same version of the Web API libraries?

If it helps, I can package up my test solution and make it available to you. Also, as a point to note, you don't need to tell Web API to find the controllers with the line you added to Global.asax, the system finds the controllers automatically provided you have them referenced.

It should work as is. Checklist

• Inherit ApiController
• End controller name with Controller. E.g. ValuesController
• Make sure WebApi project and class library project reference same WebApi assemblies
• Try to force routes using attribute routing
• Clean the solution, manually remove bin folders and rebuild
• Delete Temporary ASP.NET Files folders. WebApi and MVC cache controller lookup result
• Call `config.MapHttpAttributeRoutes(); to ensure framework takes attribute routes into consideration
• Make sure that the method you are calling is made to handle correct HTTP Verb (if it is a GET web method, you can call via browser URL, if it is POST you have to otherwise craft a web request)

This controller:

[RoutePrefix("MyValues")]
public class AbcController : ApiController
{
    [HttpGet]
    [Route("Get")]
    public string Get()
    {
        return "Ok!";
    }
}

matches this url:

http://localhost/MyValues/Get (note there is no /api/ in route because it wasn't specified in RoutePrefix.

Controller lookup caching: This is default controller resolver. You will see in the source code that it caches lookup result.

/// <summary>
/// Returns a list of controllers available for the application.
/// </summary>
/// <returns>An <see cref="ICollection{Type}" /> of controllers.</returns>
public override ICollection<Type> GetControllerTypes(IAssembliesResolver assembliesResolver)
{
    HttpControllerTypeCacheSerializer serializer = new HttpControllerTypeCacheSerializer();

    // First, try reading from the cache on disk
    List<Type> matchingTypes = ReadTypesFromCache(TypeCacheName, IsControllerTypePredicate, serializer);
    if (matchingTypes != null)
    {
        return matchingTypes;
    }
...
}