Using Custom IHttpActionInvoker in WebAPI for Exception Handling

Question

I'm trying to add a custom IHttpActionInvoker to my WebAPI application in order to prevent the need for lots of repeated exception handling code in my action methods.

There really doesn't seem to be much out there about how to do this other than this article. After writing my IHttpActionInvoker as per the article I added this code:

GlobalConfiguration.Configuration.Services.Remove(typeof(IHttpActionInvoker),
GlobalConfiguration.Configuration.Services.GetActionInvoker());

GlobalConfiguration.Configuration.Services.Add(typeof(IHttpActionInvoker),
new MyApiControllerActionInvoker());

Into a method within my Global.asax file. Now when executing a call to my API I get the following exception raised at the Remove() method:

The service type IHttpActionInvoker is not supported

I guess I have two questions.

1. Considering there doesn't seen to be an awful lot out there about writing custom IHttpActionInvoker classes is this considered a good approach to solve exception handling in WebAPI applications?

2. Does anyone know why I would get such an exception when executing the Remove() method and how best to fix this particular issue?

Answer 1

I suffered the same error you describe when attempting to remove the service.

I discovered I didn't need to remove anything from the global config, as it appears if you've registered the interface in your container then it will resolve this first.

For example, I'm using SimpleInjector and in my global.asax I have this:

container.Register<IHttpActionInvoker , MyApiControllerActionInvoker >();
// Register the dependency resolver.
GlobalConfiguration.Configuration.DependencyResolver =
   new SimpleInjectorWebApiDependencyResolver(container);

At runtime, it is resolving MyApiControllerActionInvoker dependency when required.

You can then perform exception handling in your customer ActionInvoker and any dependencies set in your constructor will be wired up correctly. The reason I was looking at the ActionInvoker was to get the constructor injection, since injecting into Attributes appears to require property injection.

Also rather than the remove/insert, replace seems to work. (in Global.asax)

GlobalConfiguration.Configuration.Services.Replace(typeof(IHttpActionInvoker), new MyApiControllerActionInvoker(fooService));

Answer 2

Have you considered registering an exception filter instead? Here's some documentation about that:

http://www.asp.net/web-api/overview/web-api-routing-and-actions/exception-handling

You shouldn't have to fall down to the action invoker layer if all you want to do is handle some exceptions in a particular way.