Web API 2：如何启用OPTIONS请求方法

Question

到目前为止，我正在尝试在API中允许Options请求方法

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        // Web API configuration and services
        var cors = new EnableCorsAttribute("*", "*", "*");
        var json = config.Formatters.JsonFormatter;
        json.SerializerSettings.PreserveReferencesHandling = Newtonsoft.Json.PreserveReferencesHandling.Objects;
        config.Formatters.Remove(config.Formatters.XmlFormatter);

        config.EnableCors(cors);

        // Web API routes
        config.MapHttpAttributeRoutes();

        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "api/{controller}/{action}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );
    }

    public static void Application_BeginRequest(object sender, EventArgs e)
    {
        if (HttpContext.Current.Request.HttpMethod == "OPTIONS")
        {
            //These headers are handling the "pre-flight" OPTIONS call sent by the browser
            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Origin", "*");
            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Methods", "GET, POST, PUT, PATCH, DELETE, OPTIONS");
            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Headers", "X-PINGOTHER, Content-Type, Authorization, Content-Length, X-Requested-With");
            HttpContext.Current.Response.AddHeader("Access-Control-Allow‌​-Credentials", "true");
            HttpContext.Current.Response.AddHeader("Access-Control-Max-Age", "1728000");
            HttpContext.Current.Response.End();
        }
    }
}

但是我仍然收到错误消息

  

从原点“ http://localhost:64556/api/post/addLike”到“ http://localhost:8081”处对XMLHttpRequest的访问已被CORS策略阻止：对预检请求的响应未通过访问控制检查：否'Access-Control-Allow-来源的标头出现在请求的资源上。

我在做什么错了？