"The parameters dictionary contains a null entry for parameter" - How to fix?

Question

I am trying to implement an edit page in order administrator to modify data in database.Unfortunately I am encountering an error.

The code below:

public ViewResult Edit(int productId) {
       // Do something here 
}

but I am getting this error:

"The parameters dictionary contains a null entry for parameter 'productId' of non-nullable type 'System.Int32' for method 'System.Web.Mvc.ViewResult Edit(Int32)' in 'WebUI.Controllers.AdminController'. To make a parameter optional its type should be either a reference type or a Nullable type.
Parameter name: parameters"

I changed my route in Global.asax.cs like this:

 routes.MapRoute(
"Admin",
"Admin/{action}/{ productId}",
new { controller = "Admin", action = "Edit",  productId= "" }
);

but still I am getting the error .

Answer 1

That empty string for productId (in your default route) will get parsed to a null entry by the Framework, and since int does not allow null...you're getting the error.

Change:

public ViewResult Edit(int productId)

to

public ViewResult Edit(int? productId)

if you want to allow for the caller to not have to pass in a product id, which is what it looks like what you want to do based on the way your route is configured.

You could also re-configure your default route to pass in some known default for when no productId is supplied:

routes.MapRoute( 
    "Admin", 
    "Admin/{action}/{ productId}", 
    new { controller = "Admin", action = "Edit",  productId= -1 } 

Answer 2

I came across the same problem following the worked SportStore example in Pro ASP.Net

The solution was actually that my Index view has the following code.

@Html.ActionLink("Edit", "Edit", new { id=item.ProductID }) |

However my Edit method in my controller was defined as

public ViewResult Edit(int productId)

changing my Index view to read

@Html.ActionLink("Edit", "Edit", new { productId=item.ProductID }) |

fixed the problem

Answer 3

Here is the way how to ignore such argument errors for any controller method invoke:

public class MyControllerBase
{
   //...

   protected override void OnActionExecuted(ActionExecutedContext filterContext)
   {
       if (filterContext.Exception != null)
       {
           var targetSite = filterContext.Exception.TargetSite;
           if (targetSite.DeclaringType != null)
               if (targetSite.DeclaringType.FullName == typeof(ActionDescriptor).FullName)
                   if (targetSite.Name == "ExtractParameterFromDictionary")  // Note: may be changed in future MVC versions
                   {
                       filterContext.ExceptionHandled = true;
                       filterContext.Result = new HttpStatusCodeResult((int)HttpStatusCode.BadRequest);
                       return;
                   }
           //...
        }
        // ...
    }
}

Answer 4

productId should be constrained to int type.

new {controller="Admin", action="Edit"},
new {productId = @"\d+" }