How to add item to the beginning of List?

Question

I want to add a \"Select One\" option to a drop down list bound to a List.

Once I query for the List, how do I add my in

Answer 1

Use Insert method of List<T>:

List.Insert Method (Int32, T): Inserts an element into the List at the specified index.

var names = new List<string> { "John", "Anna", "Monica" };
names.Insert(0, "Micheal"); // Insert to the first element

Answer 2

Use the Insert method:

ti.Insert(0, initialItem);

Answer 3

Update: a better idea, set the "AppendDataBoundItems" property to true, then declare the "Choose item" declaratively. The databinding operation will add to the statically declared item.

<asp:DropDownList ID="ddl" runat="server" AppendDataBoundItems="true">
    <asp:ListItem Value="0" Text="Please choose..."></asp:ListItem>
</asp:DropDownList>

http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.listcontrol.appenddatabounditems.aspx

-Oisin

Answer 4

Since .NET 4.7.1, you can use the side-effect free Prepend() and Append(). The output is going to be an IEnumerable.

// Creating an array of numbers
var ti = new List<int> { 1, 2, 3 };

// Prepend and Append any value of the same type
var results = ti.Prepend(0).Append(4);

// output is 0, 1, 2, 3, 4
Console.WriteLine(string.Join(", ", results ));

Answer 5

Use List<T>.Insert

While not relevant to your specific example, if performance is important also consider using LinkedList<T> because inserting an item to the start of a List<T> requires all items to be moved over. See When should I use a List vs a LinkedList.