Unity Attribute Interception with ASP.NET Web Api

Question

I'm trying to use Unity to apply a call handler via an attribute against my ApiController method, but the call handler is never invoked.

Attribute:

public class LogAttribute : HandlerAttribute
{
    private readonly int _order;

    public LogAttribute(int order)
    {
        _order = order;
    }

    public override ICallHandler CreateHandler(Microsoft.Practices.Unity.IUnityContainer container)
    {
        return new LoggingCallHandler
        { 
            Order = _order
        };
    }
}

The call handler:

  public class LoggingCallHandler : ICallHandler
    {
        public IMethodReturn Invoke(IMethodInvocation input, GetNextHandlerDelegate getNext)
        {
          //.....stuff   
        }
    }

Registration:

container.AddNewExtension<Interception>();
container.RegisterType<IMyApiController>();
container.Configure<Interception>()
     .SetInterceptorFor<IMyApiController>(new InterfaceInterceptor());

Dependency Resolver (using WebActiviatorEx):

public static class UnityWebApiActivator
{
    public static void Start() 
    {            
        var resolver = new UnityDependencyResolver(UnityConfig.GetConfiguredContainer());

        GlobalConfiguration.Configuration.DependencyResolver = resolver;
    }
}

Answer 1

The Web API system will use the dependency resolver to resolve the controller class (eg MyApiController ), not the interface that such controller class implements (eg IMyApiController ). I don't know of a way to make the Web API system request the interface instead (and I doubt that there is a way to do that).

One solution is to intercept the controller it self ( MyApiController ) but since it is a class, you cannot use the interface interceptor ( InterfaceInterceptor ) and instead you have to use the virtual method interceptor like this:

container.Configure<Interception>()
     .SetInterceptorFor<MyApiController>(new VirtualMethodInterceptor());

This will require that you make the action methods that you want to intercept virtual .

Please note that you can still intercept other dependencies injected to your controllers (that are defined as interfaces) via InterfaceInterceptor . This is because the Web API system will ask the container to resolve them as interfaces, not as classes.