Question

I have an extension method that I’m trying to use where you can use an enum property to create a dropdown list, and set the selected item:

public enum DefaultEnumSelectItemOptions
{
    AddDefaultItemIfEnumIsZero,
    ZeroEnumIsDefaultItem
}
public static SelectList ToSelectList(this object enumObj, DefaultEnumSelectItemOptions option = DefaultEnumSelectItemOptions.AddDefaultItemIfEnumIsZero)
{
    var asEnum = Enum.Parse(enumObj.GetType(), enumObj.ToString());
    var values = Enum.GetValues(enumObj.GetType());
    var dataItems = new List<Tuple<string, int>>();
    dataItems.Add(new Tuple<string, int>("Select One", -1));
    for (int i = 0; i < values.Length; i++)
    {
        int enumValue = (int)values.GetValue(i);
        if (enumValue == 0)
        {
            if (option != DefaultEnumSelectItemOptions.AddDefaultItemIfEnumIsZero)
            {
                dataItems.Add(new Tuple<string, int>(values.GetValue(i).ToString(), enumValue));
            }
        }
        else
        {
            dataItems.Add(new Tuple<string, int>(values.GetValue(i).ToString(), enumValue));
        }
    }
    var selectedItemValue = (int)enumObj;
    if (selectedItemValue == 0 && option == DefaultEnumSelectItemOptions.AddDefaultItemIfEnumIsZero)
    {
        selectedItemValue = -1;
    }
    return new SelectList(dataItems, "Item2", "Item1", selectedItemValue);
}

A model looks like this:

public enum PropertyTypes
{
    Unknown=0,
    Vehicle,
    Other
}

[DataContract]
public class Property : ClaimEntity
{
    [DataMember]
    public PropertyTypes PropertyType { get; set; }

    public Property()
    {
        this.PropertyType = PropertyTypes.Vehicle;
    }
}

Finally the view looks like this:

@Html.DropDownListFor(m => m.PropertyType, Model.PropertyType.ToSelectList())

When I set a breakpoint in the extension method, it appears to be correct, but the selected option is not appearing in the html.

What am I doing wrong?

edit I changed it to use the SelectListItem as suggested, however I still am not seeing the value selecting:

Answer 1

I’m actually running into this exact problem myself and discovered that the DropDownListFor (and DropDownList) helpers are a little too smart for their own good.

Even if you pass in a set of SelectListItem with one of them Selected = true, the helper will actually evaluate your model, do a Convert.ToString() on it, and attempt to match the value. If it doesn’t find the value it will select nothing.

Personally I believe this is a major mistake in MVC, one that they do not appear to be correcting in MVC4. It is a completely bogus assumption on their part that that the ToString() method of an object would match the value (rather than the display text) in a dropdown.

edit: as for ways to fix this…

1. Change your ToString() method to return the value and figure out a different way to get your display text.
2. Since you’re using an enum, you could just the string version for both your value and your display text. It will still bind fine.
3. Build your own dropdown