当我在方法中放置Rout标记时，为什么httpOptions方法不起作用

Question

我有一个问题，我不知道为什么会出现问题。

我想要的是在我的web api中调用一个方法，httpOptions动词应该返回一个HttpOkStatus，但它会返回404错误。只有在我贴上标签时才会发生这种情况  [Route("MyRoute")]，否则效果很好。

我的问题是，当我把标签放在上面时，为什么它不起作用？。

我有这段代码

[Authorize]
    [RoutePrefix("api/MergedSchemas")]
    public class MergedSchemasController : ApiController
    {


        [HttpGet]
        [Route("Schemas")]
        public HttpResponseMessage GetSchemas(string formName)
        {
          //Some code
        }
}

在Global.asax中我有这段代码：

public class WebApiApplication : System.Web.HttpApplication
    {
        protected void Application_Start()
        {
            AreaRegistration.RegisterAllAreas();
            GlobalConfiguration.Configure(WebApiConfig.Register);
            GlobalConfiguration.Configuration.MessageHandlers.Add(new OptionsHttpMessageHandler());
            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            RouteConfig.RegisterRoutes(RouteTable.Routes);
            BundleConfig.RegisterBundles(BundleTable.Bundles);
        }
    }

    public class OptionsHttpMessageHandler : DelegatingHandler
    {
        protected override Task<HttpResponseMessage> SendAsync(
        HttpRequestMessage request, CancellationToken cancellationToken)
        {
            if (request.Method == HttpMethod.Options)
            {
                var apiExplorer = 
                GlobalConfiguration.Configuration.Services.GetApiExplorer();

                var controllerRequested = request.GetRouteData().Values["controller"] as string;
                var supportedMethods = apiExplorer.ApiDescriptions.Where(d =>
                {
                    var controller = d.ActionDescriptor.ControllerDescriptor.ControllerName;
                    return string.Equals(
                        controller, controllerRequested, StringComparison.OrdinalIgnoreCase);
                })
                .Select(d => d.HttpMethod.Method)
                .Distinct();

                if (!supportedMethods.Any())
                    return Task.Factory.StartNew(
                        () => request.CreateResponse(HttpStatusCode.NotFound));

                return Task.Factory.StartNew(() =>
                {
                    var resp = new HttpResponseMessage(HttpStatusCode.OK);
                    resp.Headers.Add("Access-Control-Allow-Methods", string.Join(",", supportedMethods));
                    return resp;
                });
            }

            return base.SendAsync(request, cancellationToken);

        }
    }

我打电话的是：/api/MergedSchemas/Schemas?formName=frmBCOSEG

谢谢！