Question

I’m trying to auto submit on dropdownlist change to my controller with arguments. The POST does happen but I only get this error

The parameters dictionary contains a null entry for parameter ‘category’ of non-nullable type ‘System.Int32’ for method ‘System.Web.Mvc.ViewResult Index(System.String, System.String, Int32)’ in ‘shopping.WebUI.Controllers.HomeController’. An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter. Parameter name: parameters

I have a JQuery script

$(".autoSubmit select").change(function () {
    $(this).closest('form').submit();
});

a form on my View

@using (Html.BeginForm("Index", "Home", FormMethod.Post))
{
    @Html.Action("ShipToCountry", "Filters", new { Model.SelectedCountry })
}

but need to POST to this action

[HttpPost]
public ViewResult Index(string country, string currency, int category)
{
    var viewModel = new MainViewModel
    {
        SelectedCountry = country,
        SelectedCurrency = currency,
        Categories = category }
    };
    return View(viewModel);
}

None of the country, currency, category arguments is or can be optional.

What changes do I need to make, on the View maybe, to pass those parameters to the Action?

Thanks

Answer 1

The error states that your category parameter of Index view is NULL. You either have to change the HTML and javascript so that the category parameter gets value before posting or you can change the POST method to make category optional like this:

[HttpPost]
public ViewResult Index(string country, string currency, int? category)
{
    var viewModel = new MainViewModel
    {
        SelectedCountry = country,
        SelectedCurrency = currency,
        Categories = category }
    };
    return View(viewModel);
}

---

EDIT:

Since you can’t make parameters optional, you have to ensure in your HTML that before doing the POST, all <input> and <select> elements are correctly filled (and correctly named if they already aren’t).

In your case, the problem is with the category parameter. Assuming that the select that auto-submits is also the dropdown list of categories, you need to assure that the outputted HTML is similar to this:

<select name="category">
    <option value="1">Category 1</option>
    <option value="2">Category 2</option>
    <option value="3">Category 3</option>
</select>

The key here is that select MUST have the name category (or you should rename the parameter category in the Index method to match the name of this select) and that options MUST have integer values.

---

EDIT 2:

To add the currency and category, you need to add <input name="currency"> and <input name="category"> fields to the same <form> where your country is. Note, that it doesn’t need to be <input> specifically, it could be <select> as well, but the field’s name must be the same as the name of parameters in Index method.