Lars-Erik's blog

Before anything, I have to say that I do not advocate uncritical use of this solution. A good system should validate all input and keep its entities valid at all times. If you end up needing this one, you shold be needing it because you're creating a quick fix in a legacy system, or you're working with something that _should_ have errors. :)

My particular need just now is that I'm introducing a dropdown for a freetext field in a system I inherited. Its using LINQ to SQL datasources and no business layer what-so-ever, and I'm not about to make on on my 4 hour budget.

Anyway, according to this feedback post, I'm guessing MS isn't gonna bake this into the .net framework anytime soon.

http://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=260603

So here's an inherited DropDownList that does exactly that. :)
(Pretty quick and easy, so I guess that's why we don't get one in the box)

Note: It iterates over the items in the list one extra time, so it does degrade performance!

public class ForgivingDropDownList : DropDownList
{
	[Category("Behavior"), DefaultValue(true)]
	public bool AllowInvalidSelectedValue
	{
		get { return ViewState["allowInvalid"] != null ? (bool)ViewState["allowInvalid"] : true; }
		set { ViewState["allowInvalid"] = value; }
	}

	public override string SelectedValue
	{
		get
		{
			return base.SelectedValue;
		}
		set
		{
			if (!AllowInvalidSelectedValue)
			{
				base.SelectedValue = value;
				return;
			}

			if (this.Items.Count != 0)
			{
				if ((value == null) || (base.DesignMode && (value.Length == 0)))
				{
					this.ClearSelection();
					return;
				}
				ListItem item = this.Items.FindByValue(value);
				if (item == null)
				{
					base.SelectedValue = null;
					return;
				}

				base.SelectedValue = value;
			}
		}
	}
}

And here's some simple sample usage:

<asp:FormView ID="FormView1" runat="server">
	<EditItemTemplate>
		<cc1:ForgivingDropDownList ID="ForgivingDropDownList1" runat="server" SelectedValue='<%# Bind("Text") %>'>
			<asp:ListItem>a</asp:ListItem>
			<asp:ListItem>b</asp:ListItem>
		</cc1:ForgivingDropDownList>
	</EditItemTemplate>
</asp:FormView>


public class Thing
{
	public string Text { get; set; }
}

public partial class ForgivingDropDownPage : System.Web.UI.Page
{
	protected void Page_Load( object sender, EventArgs e )
	{
		if (!IsPostBack)
		{
			FormView1.DefaultMode = FormViewMode.Edit;
			FormView1.DataSource = new Thing[] { new Thing { Text = "c" } };
			FormView1.DataBind();
		}
	}
}

And that's it. :) Enjoy!