ASP.NET MVC (razor) Listbox multiselect values to string - asp.net-mvc

Question

I have two multi-select list boxes; one with months and one with years such as the following:
#Html.ListBoxFor(m => m.IncludeGuestsArrivedInTimeframeMonths, Model.TimeframeMonths)
#Html.ListBoxFor(m => m.IncludeGuestsArrivedInTimeframeYears, Model.TimeframeYears)
I'm saving the both values to the database as a comma separated list (string/nvarchar). The values are being like this: Months: 1,3,7; Years: 2002,2005
For some reason when I pull the values back out to the form, the months are pre-selecting in the listbox fine, but the years are not.
Any ideas?
EDIT - Additional code samples:
Controller - Manage
public ActionResult Manage(Guid id)
{
var list = _listService.GetList(id);
var model = LoadModelFromObject(list);
model.TimeframeMonths = GenerateMonthDropdown();
model.TimeframeYears = GenerateYearDropdown(model.IncludeGuestsArrivedInTimeframeYears.Split(','));
model.DaysOfWeek = GenerateDaysOfWeekDropdown();
return View(model);
}
Controller - 'Helper'
private IList<SelectListItem> GenerateYearDropdown(string[] selected)
{
var list = new List<SelectListItem>();
var startYear = DateTime.Now.Year - 10;
for (int idx = startYear; idx < startYear + 11; idx++)
{
list.Add(new SelectListItem
{
Value = idx.ToString(),
Text = idx.ToString(),
Selected = selected != null && selected.Contains(idx.ToString())
});
}
return list;
}
View
#Html.CheckBoxFor(m => m.IncludeGuestsArrivedInTimeframe)
#Html.LabelFor(m => m.IncludeGuestsArrivedInTimeframe)
#Html.ListBoxFor(m => m.IncludeGuestsArrivedInTimeframeMonths, Model.TimeframeMonths)
#*#Html.ListBoxFor(m => m.IncludeGuestsArrivedInTimeframeYears, Model.TimeframeYears)*#
#Html.ListBox("IncludeGuestsArrivedInTimeframeYears", Model.TimeframeYears)

Answer 1

You need to set Selected property of SelectItemList class to true for the options which you want to be pre-selected.
Example:
#{
var foo = new List<SelectListItem> {
new SelectListItem { Text = "Foo 1", Value = "1", Selected = true },
new SelectListItem { Text = "Foo 2", Value = "2" },
new SelectListItem { Text = "Foo 3", Value = "3", Selected = true }
};
}
#Html.ListBox("foo", foo)
In this case, Foo 1 and Foo 3 should appear as pre-selected. The above code generates the below html markup:
<select id="foo" multiple="multiple" name="foo">
<option selected="selected" value="1">Foo 1</option>
<option value="2">Foo 2</option>
<option selected="selected" value="3">Foo 3</option>
</select>
Edit:
First of all, replace this code:
list.Add(new SelectListItem {
Value = idx.ToString(),
Text = idx.ToString(),
Selected = selected != null && selected.Contains(idx.ToString())
});
with this code:
list.Add(new SelectListItem {
Value = idx.ToString(),
Text = idx.ToString(),
Selected = true
});
Then run the app. If all the options are pre-selected, then I bet that this selected != null && selected.Contains(idx.ToString()) does not satisfy the condition.

Answer 2

Another way of doing it
#Html.ListBox("categoryId", new MultiSelectList(ViewData["categories"] as System.Collections.IEnumerable, "Id", "CategoryName", Model.tIdx_ProductCategories.Select(x => x.CategoryId).AsEnumerable()))
Explanation:
categoryId - would be name of control, when rendered as html
ViewData["categories"] - is list of categories with Id and CategoryName properties
Model.tIdx_ProductCategories carries the list of category ids to be selected in list box.

Answer 3

As it seems (e.g. here Preselect Items in Multiselect-Listbox (MVC3 Razor)) the Razor engine happily ignores the Selected property and compares the list from the model and the supplied option list by calling ToString() on the objects from the model and using string comparison to select.
What I cannot explain to myself is why this behavior is used with Html.ListBox(), which does not use any model and expects a collection of SelectListItem.
Think it's a bug, but it does not seem to have been addressed recently.