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

Question

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 decla

Answer 1

Try adding a string for the name of your dropdown list as the first parameter, and get the item out of your viewdata:

 <%= Html.DropDownList("SomeDropdownName", (IEnumerable<SelectListItem>)ViewData["basetype"]) %>

Here is also an extension method you can use so the dropdown list is set up in a similar style to how you have done your other controls:

        public static string DropDownList<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<SelectListItem> selectList, string optionLabel)
        where TModel : class
    {
        string inputName = ExpressionHelper.GetInputName(expression);
        return htmlHelper.DropDownList(inputName, selectList, optionLabel);
    }

For example

<%= Html.DropDownList(x => x.BaseType, (IEnumerable<SelectListItem>)ViewData["basetype"], "")%>

Answer 2

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>)

Answer 3

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...