Inject WebAPI UrlHelper into service using Autofac

Question

I have a service used by a few controllers in my WebAPI project. The service needs to generate URLs, so ideally it would get a UrlHelper via a constructor parameter

Answer 1

Best I can think of is make your service implement IAutofacActionFilter like so

public class MyService : IAutofacActionFilter
    {
        private UrlHelper _urlHelper;

        public void DoSomething()
        {
            var link = Url.Link("SomeRoute", new {});
        }

        private UrlHelper Url
        {
            get
            {
                if(_urlHelper == null)
                    throw new InvalidOperationException();

                return _urlHelper;
            }
        }

        public void OnActionExecuted(System.Web.Http.Filters.HttpActionExecutedContext actionExecutedContext)
        {            
        }

        public void OnActionExecuting(System.Web.Http.Controllers.HttpActionContext actionContext)
        {
            this._urlHelper = actionContext.Request.GetUrlHelper();
        }
    }

and then use something like the following Autofac config

builder.RegisterType()
                 .AsWebApiActionFilterFor()
                 .AsSelf()
                 .InstancePerApiRequest();