Retrieving Dropdown List Value in MVC

Question

I'm trying to get the selected value of a dropdown from the Edit view to the controller. I keep getting the same error "{"Value cannot be null.\r\nParameter name: items"}"

Here is my view:

<div class="form-group">
    @Html.LabelFor(model => model.adminID, htmlAttributes: new { @class = "control-label col-md-2" })
    <div class="col-md-10">
        @Html.DropDownListFor(model => model.adminID, new SelectList(ViewBag.Admins, "Value", "Text"), htmlAttributes: new { @class = "form-control", @name = "admin" })
        @Html.ValidationMessageFor(model => model.adminID, "", new { @class = "text-danger" })
    </div>
</div>

I created the SelectList in the get action.

var admins = from a in db.members
                     select new { name = a.student.Fname + " " + a.student.Sname, id = a.StudentID };

ViewBag.Admins = admins.Select(a => new SelectListItem
{
    Text = a.name,
    Value = a.id
}).ToList();

And here is the controller. I used adminID, the name of the property to try bind it but it returns the error when I post the page.

public async Task<ActionResult> Edit([Bind(Include = "ClubId,ClubName,CreationDate,adminID")] Club club)
{
    if (ModelState.IsValid)
    {
        db.Entry(club).State = EntityState.Modified;
        await db.SaveChangesAsync();
        return RedirectToAction("Index");
    }
    return View(club);
}

The Error being returned is

"{"Value cannot be null.\r\nParameter name: items"}"

Any ideas why the adminID won't save/bind?

Route Config

public class RouteConfig
{
    public static void RegisterRoutes(RouteCollection routes)
    {
        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

        routes.MapRoute(
            name: "Default",
            url: "{controller}/{action}/{id}",
            defaults: new { controller = "Clubs", action = "Index", id = UrlParameter.Optional }
        );
    }
}

show the line of exception as well as the controller action definition plz — Steve, Dec 19 '16 at 19:37
@Steve the controller action is in the initial question (3rd snippet of code). And the exception line is attached in the screenshot, located at the top of the screenshot. — Ryan Spain, Dec 19 '16 at 19:40
@RyanSpain in MVC, you have a routesconfig. My guess is that somewhere in there, you have a routes issue. The route is expecting a parameter named items. — Jesse Moreland, Dec 19 '16 at 19:41

score 0 · Answer 1 · answered Dec 19 '16 at 19:56

0

The name of the DropdownListFor must have the same name as property of the object, otherwise use FormCollection, get value from form instance and assign to the property

answered Dec 19 '16 at 19:56

Shaahin

1,195
3
14
22

Jesse Moreland · Answer 2 · 2016-12-19T21:46:40.673

0

I think that since you're naming the drop down list as "admin", when it posts back, MVC doesn't know where to stick the value because you don't have a value in the post method's parameters named admin.

If you remove the @name, it should work.

@Html.DropDownListFor(model => model.adminID, new SelectList(ViewBag.Admins, "Value", "Text"), htmlAttributes: new { @class = "form-control" })

Another thing, You're creating a new select list in the controller then passing it into the viewdata, so you have a select list in the view data at this point. Then in the view, you're declaring another select list so you have a SelectList of SelectLists with one element.

edited Dec 19 '16 at 21:46

answered Dec 19 '16 at 20:05

Jesse Moreland

441
6
17

I actually tried this as suggested by someone else. It returns the same error. – Ryan Spain Dec 19 '16 at 20:10
Added more to the answer. – Jesse Moreland Dec 19 '16 at 21:33

Retrieving Dropdown List Value in MVC

2 Answers2