MVC 4 Html.ListBoxFor Model MultiSelectList IEnumerable Error?

I have successfully using the Html.ListBox with a ViewData like so:

[Action}
ViewData["GroupsList"] = new MultiSelectList(myGroups.GetAllGroups(), "GroupID", "GroupName");

[View]
@Html.ListBox("lbxGroups", (MultiSelectList)ViewData["GroupsList"], new { SelectionMode = "Single" })

Now I want to use the Model and having issues doing so.

I received this error when using Model.UserGroupList:

"The parameter 'expression' must evaluate to an IEnumerable when multiple selection is allowed."

Note: the Action returns the correct data.

[Action]
public ActionResult Index()
{
       ManagerViewModel viewModel = new ManagerViewModel()
       {
                UserGroupsList = new MultiSelectList(myGroups.GetAllGroups(), "GroupID", "GroupName")
       };
            return View(viewModel);
}

[View]
@model ProjectUI.ManagerViewModel
@Html.ListBoxFor(model => model.GroupId, new MultiSelectList(Model.UserGroupsList, "Value", "Text"), new { SelectionMode = "Single" }))

[Models]
public class ManagerViewModel
{
        public int GroupId { get; set; }
        public MultiSelectList UserGroupsList { get; set; }
}
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Imran Javed ZiaConsultant Software Engineer - .NET ArchitectCommented:
Hi,

If you have single selection, then technically you may use dropdown. Please try following:

@Html.ListBoxFor(model => model.GroupId,
                new SelectList(Model.UserGroupsList, "Value", "Text"))


for more information, please refer to following:
http://code.msdn.microsoft.com/Using-the-DropDownList-67f9367d


Thanks

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WorknHardrAuthor Commented:
Same error:
"The parameter 'expression' must evaluate to an IEnumerable when multiple selection is allowed."

Until.... I change the Action to SelectList from MultiSelectList like so:

     ManagerViewModel viewModel = new ManagerViewModel()
            {
                UserGroupsList = new SelectList(myGroups.GetAllGroups(), "GroupID", "GroupName")
            };

Q. Why do I find code snippets elsewhere using the MultiSelectList?
WorknHardrAuthor Commented:
Just tried this example and get the same working result as your suggestion, without using a SelectList in the view.

stackoverflow.com/questions/1255472/how-does-a-multiple-select-list-work-with-model-binding-in-asp-net-mvc

View model:
public class MyViewModel
{
    public int[] SelectedIds { get; set; }
    public IEnumerable<SelectListItem> Items { get; set; }
}

Controller:
public ActionResult Index()
{
    var model = new MyViewModel
    {
        // fetch the items from some data source
        Items = Enumerable.Select(x => new SelectListItem
        {
            Value = x.Id,
            Text = "item " + x.Id
        })
    };
    return View(model);
}

View:
@model MyViewModel
@Html.ListBoxFor(x => x.SelectedIds, Model.Items)
WorknHardrAuthor Commented:
thx
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