ASP.NET MVC - Problem passing parameters to the controller

Question

I have a controller with an action method as follows:

public class InventoryController : Controller
{
    public ActionResult ViewStockNext(int firstItem)
    {
        // Do some stuff
    }
}

And when I run it I get an error stating:

The parameters dictionary does not contain a valid value of type 'System.Int32' for parameter 'firstItem'. To make a parameter optional its type should either be a reference type or a Nullable type.

I had it working at one point and I decided to try the function without parameters. Finding out that the controller was not persistant I put the parameter back in, now it refuses to recognise the parameter when I call the method.

I'm using this url syntax to call the action:

http://localhost:2316/Inventory/ViewStockNext/11

Any ideas why I would get this error and what I need to do to fix it? I've tried adding another method that takes an integer to the class it it also fails with the same reason. I've tried adding one that takes a string, and the string is set to null. I've tried adding one without parameters and that works fine, but of course it won't suit my needs.

Any help would be appreciated.

Thanks Daniel

Answer 1

Your routing needs to be set up along the lines of {controller}/{action}/{firstItem}. If you left the routing as the default {controller}/{action}/{id} in your global.asax.cs file, then you will need to pass in id.

routes.MapRoute(
    "Inventory",
    "Inventory/{action}/{firstItem}",
    new { controller = "Inventory", action = "ListAll", firstItem = "" }
);

... or something close to that.

Answer 2

To rephrase Jarret Meyer's answer, you need to change the parameter name to 'id' or add a route like this:

routes.MapRoute(
        "ViewStockNext", // Route name
        "Inventory/ViewStockNext/{firstItem}",  // URL with parameters
        new { controller = "Inventory", action = "ViewStockNext" }  // Parameter defaults
    );

The reason is the default route only looks for actions with no parameter or a parameter called 'id'.

Edit: Heh, nevermind Jarret added a route example after posting.

Answer 3

Or, you could try changing the parameter type to string, then convert the string to an interger in the method. I am new to MVC, but I believe you need nullable objects in your parameter list, how else will the controller indicate that no such parameter was provided? So...

public ActionResult ViewNextItem(string id)...

Answer 4

public ActionResult ViewNextItem(int? id) makes the id integer a nullable type, no need for string<->int conversions.

Answer 5

There is another way to accomplish that (described in more details in Stephen Walther's Pager example

Essentially, you create a link in the view:

Html.ActionLink("Next page", "Index", routeData)

In routeData you can specify name/value pairs (e.g., routeData["page"] = 5), and in the controller Index function corresponding parameters receive the value. That is,

public ViewResult Index(int? page)

will have page passed as 5. I have to admit, it's quite unusual that string ("page") automagically becomes a variable - but that's how MVC works in other languages as well...