[c#] Best way to check if a drop down list contains a value?

When the user navigates to a new page, this ddl's selected index is determined by a cookie, but if the ddl doesn't contain that cookie's value, then I'd like it to be set the 0. What method would I use for the ddl? Is a loop the best way, or is there a simply if statement I can perform?

This is what I've attempted, but it doesn't return a bool.

if ( !ddlCustomerNumber.Items.FindByText( GetCustomerNumberCookie().ToString() ) )
    ddlCustomerNumber.SelectedIndex = 0;

On C# this works:

        if (DDLAlmacen.Items.Count > 0)
        {
            if (DDLAlmacen.Items.FindByValue("AlmacenDefectoAndes").Value == "AlmacenDefectoAndes")
            {
                DDLAlmacen.SelectedValue = "AlmacenDefectoAndes";
            }
        }

Update:

Translating the code above to Visual Basic doesn't work. It throws "System.NullReferenceException: Object reference not set to an instance of an object.."

So. for this to work on Visual Basic, I had to change the code like this:

        If DDLAlmacen.Items.Count > 0 Then
            If DDLAlmacen.Items.Contains(New ListItem("AlmacenDefectoAndes")) Then
                DDLAlmacen.SelectedValue = "AlmacenDefectoAndes"
            End If
        End If

What about this:

ListItem match = ddlCustomerNumber.Items.FindByText(
    GetCustomerNumberCookie().ToString());
if (match == null)
    ddlCustomerNumber.SelectedIndex = 0;
//else
//    match.Selected = true; // you'll probably select that cookie value

You could try checking to see if this method returns a null:

if (ddlCustomerNumber.Items.FindByText(GetCustomerNumberCookie().ToString()) != null)
    ddlCustomerNumber.SelectedIndex = 0;

That will return an item. Simply change to:

if (ddlCustomerNumber.Items.FindByText( GetCustomerNumberCookie().ToString()) != null)
    ddlCustomerNumber.SelectedIndex = 0;

If 0 is your default value, you can just use a simple assignment:

ddlCustomerNumber.SelectedValue = GetCustomerNumberCookie().ToString();

This automatically selects the proper list item, if the DDL contains the value of the cookie. If it doesn't contain it, this call won't change the selection, so it stays at the default selection. If the latter one is the same as value 0, then it's the perfect solution for you.

I use this mechanism quite a lot and find it very handy.

If the function return Nothing, you can try this below

if (ddlCustomerNumber.Items.FindByText(
    GetCustomerNumberCookie().ToString()) != Nothing)
{
...
}

Sometimes the value needs to be trimmed of whitespace or it won't be matched, in such case this additional step can be used (source):

if(((DropDownList) myControl1).Items.Cast<ListItem>().Select(i => i.Value.Trim() == ctrl.value.Trim()).FirstOrDefault() != null){}

//you can use the ? operator instead of if

ddlCustomerNumber.SelectedValue = ddlType.Items.FindByValue(GetCustomerNumberCookie().ToString()) != null ? GetCustomerNumberCookie().ToString() : "0";

ListItem item = ddlComputedliat1.Items.FindByText("Amt D");
if (item == null) {
    ddlComputedliat1.Items.Insert(1, lblnewamountamt.Text);
}