The ViewData item that has the key 'MY KEY' is of type 'System.String' but must be of type 'IEnumerable<SelectListItem>'

I am trying to populate a dropdown list from a database mapped with Linq-2-SQL, using ASP.NET MVC 2, and keep getting this error.

I am so confused because I am declaring a variable of type IEnumerable<SelectListItem> on the second line, but the error makes me think this is not the case. I feel like this should be very simple, but I am struggling. Any help is appreciated.

Here are the interesting bits of my controller:

public ActionResult Create()
{
    var db = new DB();
    IEnumerable<SelectListItem> basetypes = db.Basetypes.Select(
        b => new SelectListItem { Value = b.basetype, Text = b.basetype });
    ViewData["basetype"] = basetypes;
    return View();
}

And here are the interesting bits of my view:

<div class="editor-label">
   <%: Html.LabelFor(model => model.basetype) %>
</div>
<div class="editor-field">
   <%: Html.DropDownList("basetype") %>
   <%: Html.ValidationMessageFor(model => model.basetype) %>
</div>

Here is the POST action when submitting the Form

// POST: /Meals/Create
[HttpPost]
public ActionResult Create(Meal meal)
{
    if (ModelState.IsValid)
    {
        try
        {
            // TODO: Add insert logic here
            var db = new DB();
            db.Meals.InsertOnSubmit(meal);
            db.SubmitChanges();
            return RedirectToAction("Index");
        }
        catch
        {
            return View(meal);
        }
    }
    else
    {
        return View(meal);
    }
}

Thanks.

Solution 1:

I had same problem, and finally I got the answer...

The problem is that in the POST action, after submitting the form, the ModelState is not valid, or it's catching an error in try/catch, so the View is returned. But this time the View has not the ViewData["basetype"] correctly set.

You need to populate it again, probably with the same code used before, so repeat this:

var db = new DB();
IEnumerable<SelectListItem> basetypes = db.Basetypes.Select(
    b => new SelectListItem { Value = b.basetype, Text = b.basetype });
ViewData["basetype"] = basetypes;

before the return View(meal) in the [HttpPost] method.

exactly this will solve your problem:

[HttpPost]
public ActionResult Create(Meal meal)
{
    if (ModelState.IsValid)
    {
        try
        {
            // TODO: Add insert logic here
            var db = new DB();
            db.Meals.InsertOnSubmit(meal);
            db.SubmitChanges();
            return RedirectToAction("Index");
        }
        catch
        {
            var db = new DB();
            IEnumerable<SelectListItem> basetypes = db.Basetypes.Select(
               b => new SelectListItem { Value = b.basetype, Text = b.basetype });
            ViewData["basetype"] = basetypes;
            return View(meal);
        }
    }
    else
    {
        var db = new DB();
        IEnumerable<SelectListItem> basetypes = db.Basetypes.Select(
            b => new SelectListItem { Value = b.basetype, Text = b.basetype });
        ViewData["basetype"] = basetypes;
        return View(meal);
    }
}

I know this question is very old, but I came here today with the same problem, so other could come here later...

Solution 2:

You will receive this error if the SelectList is null.

Solution 3:

I've just come across this issue and this article helped me through it - http://odetocode.com/Blogs/scott/archive/2010/01/18/drop-down-lists-and-asp-net-mvc.aspx

The most likely cause it that your collection is repopulated after the po

Solution 4:

For future readers, if you are using razor, try to change type of selectlist item from List to IEnumerable.

From

@Html.DropDownListFor(m => m.id, ViewBag.SomeList as List<SelectListItem>)

To

@Html.DropDownListFor(m => m.id, ViewBag.SomeList as IEnumerable<SelectListItem>)