Problems issuing DropDownList.Items.Addrange and selecting a value

Question

I'm new to C#, as I mainly have been using Java.

But straight to the problem (which I have simplified a bit):

First an excerpt of my aspx-page:

<div class="dates">
    <div class="firstselection">
        <asp:DropDownList ID="DDFromMonth" runat="server">
        </asp:DropDownList>
        <asp:DropDownList ID="DDToMonth" runat="server">
        </asp:DropDownList>
    </div>
</div>

And the codebehind:

    public partial class Argh: System.Web.UI.Page
    {
  static  List<ListItem> monthList = new List<ListItem>
  {
   new ListItem("Jan", "1"),
   new ListItem("Feb", "2"),
   new ListItem("Mar", "3"),
   new ListItem("Apr", "4"),
   new ListItem("May", "5"),
   new ListItem("Jun", "6"),
   new ListItem("Jul", "7"),
   new ListItem("Aug", "8"),
   new ListItem("Sep", "9"),
   new ListItem("Oct", "10"),
   new ListItem("Nov", "11"),
   new ListItem("Dec", "12")
  };



        protected void Page_Load(object sender, EventArgs e)
        {
   DDFromMonth.Items.AddRange(monthList.ToArray());  // DDFromMonth is a asp.net dropdown list
   DDToMonth.Items.AddRange(monthList.ToArray()); // DDToMonth is a asp.net dropdown list

            DDFromMonth.SelectedValue = "6"; 
            DDToMonth.SelectedValue = "7"; // also changes DDFromMonth value (GODDAMN!)

 }

Ok, I have a static list that contains the months. I add the range of this list to both dropdown-controls and DDFromMonth I select "6" (June) and DDToMonth "7" (July). However, this results in both dropdownlists show July!

I also tried with a non-static list, but that doesn't matter. The only thing I tested that "works" is to instantiate two different lists - only then the dropdownlist-items are selected as I wish. So, adding the lists like this make things work (but is ugly):

DDFromMonth.Items.AddRange(monthList.ToArray());
DDFromMonth.Items.AddRange(aDuplicatedMonthList.ToArray()); 

I have worked around this by adding datasources via asp.net, but still, it would be interesting to know what is happening here. Why do I have to instantiate a new list for each dropdown list. Doesn't each control have own pointers that keep track of their own values? It feels like the pointers are shared in the list somehow, but I leave ponderings to someone that better knows C# and ASP.NET

Answer 1

ListItems are added directly to the DropDownList control. So in effect what you are doing is adding the EXACT same list to 2 different controls. Therefore, only the LAST selected item will be implemented, because the same list can only have ONE selected ListItem.

A simple way to do what you want would be this:

protected ListItem[] MonthList
{
   get
   {
      return new ListItem[]
      {
       new ListItem("Jan", "1"),
       new ListItem("Feb", "2"),
       new ListItem("Mar", "3"),
       new ListItem("Apr", "4"),
       new ListItem("May", "5"),
       new ListItem("Jun", "6"),
       new ListItem("Jul", "7"),
       new ListItem("Aug", "8"),
       new ListItem("Sep", "9"),
       new ListItem("Oct", "10"),
       new ListItem("Nov", "11"),
       new ListItem("Dec", "12")

       };
}

Now you'll always create a new array.