ASP.NET MVC MultiSelectList with selected values not selecting properly

Question

I know others have asked this question, but I\'m totally confused by this:

This displays the dropdown with no values selected:

<%= Html.DropDownLi         


        

Answer 1

Too little context provided in your question but I will try to show a full working example:

Model:

public class Item
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class MyModel
{
    public IEnumerable SelectedItemIds { get; set; }
    public IEnumerable AvailableItems { 
        get 
        {
            return new[] 
            {
                new Item { Id = 1, Name = "Item 1" },
                new Item { Id = 2, Name = "Item 2" },
                new Item { Id = 3, Name = "Item 3" },
            };
        } 
    }
}

Controller:

[HandleError]
public class HomeController : Controller
{
    public ActionResult Index()
    {
        var model = new MyModel
        {
            SelectedItemIds = new[] { 2, 3 }
        };
        return View(model);
    }

    [HttpPost]
    public ActionResult Index(IEnumerable selectedItemIds)
    {
        var model = new MyModel
        {
            // Important: Don't ever try to modify the selectedItemIds here
            // The Html helper will completely ignore it and use 
            // the POSTed values
            SelectedItemIds = selectedItemIds
        };
        return View(model);
    }
}

View:

<% using (Html.BeginForm()) { %>
    <%= Html.ListBoxFor(x => x.SelectedItemIds, 
        new MultiSelectList(Model.AvailableItems, "Id", "Name")) %>
    
<% } %>

Notice that the Html.ListBoxFor is more adapted if you want to generate a multiple select. Obviously the AvailableItems property should be fetched from a repository.