Sure as always you start by defining a view model that will represent the information you would like to show on the particular view:
public class MyViewModel
{
public string[] SelectedItems { get; set; }
public IEnumerable<SelectListItem> Items { get; set; }
}
then a controller:
public class HomeController : Controller
{
public ActionResult Index()
{
var model = new MyViewModel
{
SelectedItems = new[] { "1", "3" },
Items = new[]
{
new SelectListItem { Value = "1", Text = "Item 1" },
new SelectListItem { Value = "2", Text = "Item 2" },
new SelectListItem { Value = "3", Text = "Item 3" },
}
};
return View(model);
}
}
and finally in your strongly typed view:
<%= Html.ListBoxFor(
x => x.SelectedItems,
new SelectList(Model.Items, "Value", "Text")
) %>
As expected Item 1 and Item 3 will be preselected when the list box is rendered.