DropDownList with LinqDataSource and an empty option

Question

Is there some elegant way to add an empty option to a DropDownList bound with a LinqDataSource?

Answer 1

Here's how to add a value at the top of the list. It can be an empty string, or some text.

<asp:DropDownList ID="categories" runat="server" AppendDataBoundItems="True" AutoPostBack="True" DataSourceID="categoriesDataSource" DataTextField="CategoryName" DataValueField="CategoryID" EnableViewState="False">
    <asp:ListItem Value="-1">
       -- Choose a Category --
    </asp:ListItem>           
</asp:DropDownList>

Be sure to set the DropDownList's AppendDataBoundItems=True.

Answer 2

I'd provide an extension method on IEnumerable<string> that prepended an item to the beginning of the list:

 public static IEnumerable<string> Prepend(this IEnumerable<string> data, string item)
 {
  return new string[] { item == null ? string.Empty : item }.Union(data);
 }

Its sort of linq-y, as it uses the linq extension method Union. Its a little cleaner than doing this:

var result = new string[]{string.Empty}.Union(from x in data select x.ToString());

Answer 3

Markup:

<asp:DropDownList ID="ddlQualQuestion" runat="server" DataSourceID="sdsQualQuestion" DataTextField="ShortQuestionText" DataValueField="QualificationQuestionKey" AutoPostBack="true" OnSelectedIndexChanged="ddlQualQuestion_SelectedIndexChanged" OnDataBound="ddlQualQuestion_DataBound" />

Code behind: protected void ddlQualQuestion_DataBound(object sender, EventArgs e)
{
ddlQualQuestion.Items.Insert(0, new ListItem("", "0"));
}