Web Api controller thinks it is duplicated

Question

I have a webforms app, that has some Web Api controllers in it for integrations. Two are working just fine. But Today I wanted to add another controller.

Should be simple enough, I add a new Web Api controller, add a little bit of code to it, and:

namespace MyApp.Web.App_Code
{
    public class AuthExportController : ApiController
    {
        public IEnumerable<string> Get()
        {
            return new string[] { "value1", "value2" };
        }
    }
 }

and when i call it at this url :

http://localhost:30978/MyApp/api/AuthExport

I get this error:

<Error>
    <Message>An error has occurred.</Message>
    <ExceptionMessage>Multiple types were found that match the controller named  
    'AuthExport'. This can happen if the route that services this request  
    ('api/{controller}/{id}') found multiple controllers defined with the same name but 
    differing namespaces, which is not supported. The request for 'AuthExport' has found 
    the following matching controllers: MyApp.Web.App_Code.AuthExportController  
    MyApp.Web.App_Code.AuthExportController</ExceptionMessage>

    <ExceptionType>System.InvalidOperationException</ExceptionType>

    <StackTrace> at  
    System.Web.Http.Dispatcher.DefaultHttpControllerSelector.SelectController(HttpRequestMessag
    e request) at   
    System.Web.Http.Dispatcher.HttpControllerDispatcher.SendAsyncInternal(HttpRequestMessage 
    request, CancellationToken cancellationToken) at 
    System.Web.Http.Dispatcher.HttpControllerDispatcher.SendAsync(HttpRequestMessage  
    request, CancellationToken cancellationToken)</StackTrace>
</Error>

As you can see, it is complaining about 2 controllers with the same name, but its the exact same controller. My other controllers work fine, just this particular one.

If it helps anything, this is my routing code in global.asax

protected void Application_Start(object sender, EventArgs e)
{
    RouteTable.Routes.MapHttpRoute(
        name: "DefaultApi",
        routeTemplate: "api/{controller}/{id}",
        defaults: new { id = System.Web.Http.RouteParameter.Optional }
    );

    GlobalConfiguration.Configuration.Formatters.Clear();
    GlobalConfiguration.Configuration.Formatters.Add(new XmlMediaTypeFormatter());
}

Driving me mad!

Update:

Ok I managed to fix it, but I don't understand why, so if someone could explain it to me. I compared my working controllers with my non working one. Exact same signatures exactly, nothing different, same using statements, same inheritance etc etc. One thing I did notice is the build action on the file. Working file has a build action of "Content" and the non working has a build action of "Compile" . I change my non working one to "Content" and it works.

So now I am even more confused :) Happy that it works, but I don't like black magic in my systems

Answer 1

TL;DR:

Delete bin folder in your project's file directory and build your project again.

Explanation:

I just encountered this error while renaming an existing project and changing namespaces for it and this is what happened:

Let's say projects' name was FirstName and I wanted to rename it to SecondName.

• I built project which compiled everything and generated bin/Debug/FirstName.dll files
• I renamed the project to SecondName
• I refactored the namespace
• Built and ran the project
• This generated bin/Debug/SecondName.dll

When project was ran, IIS Express simply took all of the .dll files and loaded them into memory, which happened to include both FirstName.dll and SecondName.dll.

As you might already understood, FirstName.dll and SecondName.dll had the same classes and methods, but with a different namespaces! Therefore, as both of DLLs were loaded into memory by IIS, WebApi routing mechanism was finding both of namespaces with same controllers and action names.

And there you have it. No voodoo magic after all :)