Error on run with simple ActionFilterAttribute

Question

Started writing a simple filter to pull some stuff from request on each action load, copied some code from other stackoverflows that looks like so:

public class TestKeyAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(HttpActionContext context)
    {
        if (context.Request.Properties.ContainsKey("test"))
        {
        // do stuff
        }
    }
}

Then added the attribute with the rest:

public static void RegisterGlobalFilters(GlobalFilterCollection filters)
{
    GlobalConfiguration.Configuration.Filters.Add(new ElmahHandledErrorLoggerFilter());
    filters.Add(new HandleErrorAttribute());
    filters.Add(new TestKeyAttribute());
}

On run, results in this error:

The given filter instance must implement one or more of the following filter
interfaces: IAuthorizationFilter, IActionFilter, IResultFilter, IExceptionFilter.

Most of the links I've found relate to MVC 3, and this seems to work; I am however using MVC 4 and using Web API - is there some other way I need to register the attribute now?

Just a note: I don't want the filter attached to Web API controllers (adding it to GlobalConfiguration.Configuration.Filters does work, though), but rather the normal web controllers.

Edit: I know I can get this working by inheriting from IActionFilter instead and using OnActionExecuting, I'm just curious why this approach doesn't work, since a bunch of tutorials seem to say it should.

Answer 1

I had the same error and was puzzled as ElmahHandledErrorLoggerFilter does implement IExceptionFilter.

After investigation, I kicked myself, I'd added the filters.Add(new ElmahHandledErrorLoggerFilter()); to the MVC site config under the FilterConfig class. Adding config.Filters.Add(new ElmahHandleErrorApiAttribute()); instead to the WebApiConfig class works.

Note: I'm using WebAPi v1 here but I've configured a v2 project in the same way.