Web Api Start up Exceptions with IDependencyResolver implementation

I was running in to the same issue using Unity with WebApi and OWIN/Katana.

The solution for me was to use the UnityDependencyResolver defined in the Unity.WebApi Nuget package instead of my own custom implementation (like @Omar Alani above)

Install-Package Unity.WebAPI

Note that the package will try and add a file named UnityConfig.cs in App_Start (the filename I used myself).

In that UnityConfig.cs file the package will add code to register the container against the GlobalConfiguration.Configuration.DependencyResolver which is not what we want with OWIN.

So instead of using:

GlobalConfiguration.Configuration.DependencyResolver = new UnityDependencyResolver(container);

Change to use:

config.DependencyResolver = new UnityDependencyResolver(container);

For completeness:

My UnityConfig.cs

public static class UnityConfig
{
    public static void Register(HttpConfiguration config)
    {
        var container = new UnityContainer();

        // Your mappings here

        config.DependencyResolver = new UnityDependencyResolver(container);
    }
}

My Startup.cs

[assembly: OwinStartup(typeof(UnityTest.BusinessLayer.Api.ApiStartup))]
namespace UnityTest.BusinessLayer.Api
{
    public partial class ApiStartup
    {
        public void Configuration(IAppBuilder app)
        {

            app.UseCors(Microsoft.Owin.Cors.CorsOptions.AllowAll);

            HttpConfiguration httpConfig = new HttpConfiguration();

            UnityConfig.Register(httpConfig);

            ConfigureAuth(app); //In App_Start ->Startup.Auth

            WebApiConfig.Register(httpConfig);

            app.UseWebApi(httpConfig);
    }
  }
}