ASP.NET MVC F# controller action ignoring parameter
I have a C# ASP.NET MVC project but my controllers are written in F#.
For some reason, the following code doesn't work properly:
namespace MvcApplication8.Controllers
open System.Web.Mvc
[<HandleError>]
type ImageController() =
inherit Controller()
member x.Index (i : int) : ActionResult =
x.Response.Write i
x.View() :> ActionResult
The parameter of the action is seemingly ignored...
http://localhost:56631/Image/Index/1
Results in this error message:
The parameters dictionary contains a null entry for parameter 'i' of non-nullable type 'System.Int32' for method 'System.Web.Mvc.ActionResult Index(Int32)' in 'MvcApplication8.Controllers.ImageController'. An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter.
Parameter name: parameters
The controller otherwise works fine. I know that plenty of people have written F# MVC code, so any ideas where I'm going wrong?
The problem is that the name of the parameter of the controller needs to match the name specified in the mapping that specifies how to translate the URL to a controller call.
If you look into the Global.asax.cs file (which you should be able to translate to F# too), then you would see something like this:
routes.MapRoute(
"Default", // Route name
"{controller}/{action}/{id}", // URL with parameters
new { controller = "Home", action = "Index",
id = UrlParameter.Optional } // Parameter defaults
);
The name id specifies the expected name of the parameter, so you need to adjust the F# code to take a parameter named id like this:
member x.Index(id:int) =
x.ViewData.["Message"] <- sprintf "got %d" id
x.View() :> ActionResult
You can use Nullable<int> type if you want to make the parameter optional.
For a programmer used to the static type safety provided by F#, it is somewhat surprising that ASP.NET MVC relies on so many dynamic tests that aren't checked at compile-time. I would hope that one day, there will be some nicer web framework for F# :-).
what's your Route look like? is it routing to id? in which case rename i to id
链接地址: http://www.djcxy.com/p/39218.html上一篇: 参数字典包含参数的空项