Dropdownlist in ASP.net C#

I have two dropdownlist's.DropDownList2(not bound to a datasource) and DropDownList3(bound to a datasource)

On change on input in one dropdownlist some content in the other Dropdownlist should change. For that i had used the logic as.

Autopostback is enabled for both this controls.

   protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (DropDownList2.SelectedItem.Text == "Stamp")
        {
            DropDownList3.Items.Remove(DropDownList3.Items.FindByText("STA"));
            DropDownList3.Items.Remove(DropDownList3.Items.FindByText("STM"));
        }


<asp:DropDownList ID="DropDownList3" runat="server" 
            DataSourceID="SqlDataSource1" DataTextField="skey" DataValueField="casecode" 
            AppendDataBoundItems="True" AutoPostBack="True">
            <asp:ListItem Selected="True" Value="S">Select</asp:ListItem>
        </asp:DropDownList>

Now the problem is when i select DropDownList2.SelectedItem.Text == "Reg" STA and STM are not present. I want STA and STM values back in the dropdownlist on selection of 'Reg'.

When i first load my page and select 'Reg' all the values in DropDownList3(including 'STA' and 'STM') are present and than when i select 'Stamp' the values 'STA' and 'STM' are lost(as shown in the code). Now again when i select 'Reg' this values are not there, i want this values to be present again.

What开发者_如何学C do i have to do?? Do i have to bind it again to database?

Is there any other logic for it to be used in a different way ?If anyone can help me

You can to bind DropDownList3 everytime DropDownList2 selected index change then only if the value is "Stamp" you remove the values "STA" and "STM" from DropDownList3

protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)    
{   
   // Fill DropDownList3 data source and bind it again to restore all the items
   FillDataSource(); // This method gets all the data from DropDownList3
   DropDownList3.DataBind();

   if (DropDownList2.SelectedItem.Text == "Stamp")
   {
        DropDownList3.Items.Remove(DropDownList3.Items.FindByText("STA"));
        DropDownList3.Items.Remove(DropDownList3.Items.FindByText("STM"));        
   }
   ...

If you know the values of the dropdown items, you can add them in the else clause, if you don't know the value/text combination you'll have to rebind.