Set selected value in SelectList after instantiation

Question

Am I right to think that there is no way to set the selected value in the C# class SelectList after it is created? Isn\'t that a bit silly?

Answer 1

I needed a dropdown in a editable grid myself with preselected dropdown values. Afaik, the selectlist data is provided by the controller to the view, so it is created before the view consumes it. Once the view consumes the SelectList, I hand it over to a custom helper that uses the standard DropDownList helper. So, a fairly light solution imo. Guess it fits in the ASP.Net MVC spirit at the time of writing; when not happy roll your own...

public static string DropDownListEx(this HtmlHelper helper, string name, SelectList selectList, object selectedValue)
{
    return helper.DropDownList(name, new SelectList(selectList.Items, selectList.DataValueField, selectList.DataTextField, selectedValue));
}

Answer 2

I think you can do this in the controller. If you are going to render a drop down list with name/ID StateCode, then you can set the selected state using this code after the SelectList is created:

ViewData["StateCode"] = "VT";

It seems that the drop down list HTML helper looks for a ViewData item with the same name as the drop down list that's being created.

I don't think I like using this technique, but it does seem to work.

I do agree that the SelectList class is a little weak at the moment. I'd like to be able to create a SelectList and then select a value later by either value or text.

Answer 3

You mean client-side, in the browser?

var select = document.getElementById('mySelect');
select.options[newIndex].selected = true;

Answer 4

I agree with @awrigley and others that it is better to load the selected value using the selectlist constructor in the usual case when you have a single dropdownlist. However, sometimes, one needs to set the selected value on the view, such as when you have a page with n identical dropdowns. Since it is not practical to create such collections in the controller and may not even know in advance how many dropdowns you need, a better approach is to create one instance in the viewmodel as a template with no selected value set and then dynamically create the rest dynamically on the view.

I run into this often when iterating through a list of child items on edit views when the children need dropdowns. In such cases, you can do it like this with one line of code:

@Html.DropDownListFor(x => myViewModelFieldName, new SelectList(Model.MyRawSelectListFromMyViewModel.Select(x=> new {x.Value, x.Text}), "Value", "Text", TheValueYouWantToSelect))

Answer 5

The "SelectedValue" property is read-only. Setting it in the constructor is the only way.

Tor, the SelectList is an ASP.NET MVC construct used to create a drop-down list. Doing it your way should work too, but the SelectList should do it for you (and not in JS) if done properly.

Answer 6

I know it' an old question, but it might help someone out there. I did what looks to be closely like what Erik did. I just created a new SelectList from my existing one...

SelectList myList = GetMySelectList();
SelectListItem selected = myList.FirstOrDefault(x => x.Text.ToUpper().Contains("UNITED STATES"));
if (selected != null)
{
     myList = new SelectList(myList, "value", "text", selected.Value);
}