Question

I’ve got a nullable enum that, unlike others on the same page, doesn’t work. I have an enum, Title whereby using the extension method will help to populate a drop-down list on the page. Here’s what the ViewBag declaration looks like:

ViewBag.TitleList = EnumExtensions.ToSelectList<Title>("[select]");

Now, perhaps someone could explain it to me, but this is where the black magic happens when it comes to binding in MVC. If the page is invalid when calling if(ModelState.IsValid) then upon re-rendering the screen, the above statement is called again. However this time, the correct drop-down item will be selected (dependent on which one you had selected at the time).

Digging deeper, this is the method declarations:

    public static SelectList ToSelectList<TEnum>(string nullEntry = null) where TEnum : struct
    {
        return ToSelectList<TEnum>(nullEntry, null);
    }


    public static SelectList ToSelectList<TEnum>(string nullEntry = null, string selectedValue = null) where TEnum : struct
    {
        var enumType = typeof(TEnum);
        var values = Enum.GetValues(enumType).OfType<TEnum>();
        List<SelectListItem> items =  ToSelectList<TEnum>(values, nullEntry, selectedValue);
        SelectList sl = new SelectList(items, "Value", "Text", selectedValue);
        return sl;
    }

    public static List<SelectListItem> ToSelectList<T>(this IEnumerable<T> enumerable, string nullEntry, string selectedValue = null)
    {
        List<SelectListItem> items;

        if ((typeof(T).IsEnum))
        {
            items = enumerable.Select(f => new SelectListItem()
            {
                Text = f.GetDescription(),
                Value = f.ToString(),
                Selected = f.ToString() == selectedValue
            }).ToList();
        }
        else
        {
            items = enumerable.Select(f => new SelectListItem()
            {
                Text = f.ToString(),
                Value = f.ToString()
            }).ToList();
        }

        if (!string.IsNullOrEmpty(nullEntry))
        {
            items.Insert(0, new SelectListItem() { Text = nullEntry, Value = "" });
        }

        return items;
    }

There’s just some overloads to handle random cases, although presumably some of these won’t be needed.

As I say, the correct item will be selected for other enumerations, but for this particular one, Title, it will not. Here’s the enum declaration:

public enum Title
{
    Mr,
    Miss,
    Mrs,
    Ms
}

And finally, the declaration using DropDownListFor on the page itself;

@Html.DropDownListFor(x => x.Title, (SelectList)ViewBag.TitleList)

The problem is that when I first visit the page, the selected item is always “[select]” (when the provided enum value is null in the model). However, the model property Title definitely has a value set, and the SelectedItem property is set for the drop-down list too, but on screen, it defaults to “[select]” which is unexpected.

Any ideas?

Answer 1

Could it be because of the name Title? Try changing it to another name just to see.