Cascading DropDownlist with hardcoded value using C# in ASP.Net

Hi Firuz,

I have created sample that full fill your requirement.

HTML

<div>
    <table border="1" cellpadding="0" cellspacing="0">
        <tr>
            <td>
                <asp:DropDownList ID="DropDownList1" runat="server" OnSelectedIndexChanged="OnChanged"
                    AutoPostBack="true">
                    <asp:ListItem>Select</asp:ListItem>
                    <asp:ListItem>1</asp:ListItem>
                    <asp:ListItem>2</asp:ListItem>
                    <asp:ListItem>3</asp:ListItem>
                    <asp:ListItem>4</asp:ListItem>
                </asp:DropDownList>
            </td>
            <td>
                <asp:DropDownList ID="DropDownList2" runat="server">
                    <asp:ListItem>Select</asp:ListItem>
                    <asp:ListItem>101</asp:ListItem>
                    <asp:ListItem>102</asp:ListItem>
                    <asp:ListItem>103</asp:ListItem>
                    <asp:ListItem>104</asp:ListItem>
                    <asp:ListItem>201</asp:ListItem>
                    <asp:ListItem>202</asp:ListItem>
                    <asp:ListItem>203</asp:ListItem>
                    <asp:ListItem>204</asp:ListItem>
                    <asp:ListItem>301</asp:ListItem>
                    <asp:ListItem>302</asp:ListItem>
                    <asp:ListItem>303</asp:ListItem>
                    <asp:ListItem>304</asp:ListItem>
                    <asp:ListItem>401</asp:ListItem>
                    <asp:ListItem>402</asp:ListItem>
                    <asp:ListItem>403</asp:ListItem>
                    <asp:ListItem>405</asp:ListItem>
                </asp:DropDownList>
            </td>
        </tr>
    </table>
</div>

Code

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        // Saving all the items from dropdown2 in session.
        List<string> dropdown2Items = new List<string>();
        foreach (ListItem item in DropDownList2.Items)
        {
            dropdown2Items.Add(item.Text);
        }
        Session["Items"] = dropdown2Items;
    }
}
protected void OnChanged(object sender, EventArgs e)
{
    string selectedItem = DropDownList1.SelectedItem.Text.Trim();
    DropDownList2.Items.Clear();
    List<string> filterItems = new List<string>();
    foreach (string item in Session["Items"] as List<string>)
    {
        if (item[0].ToString() == selectedItem)
        {
            filterItems.Add(item);
        }
    }
    DropDownList2.Items.Insert(0, new ListItem("Select"));
    DropDownList2.AppendDataBoundItems = true;
    DropDownList2.DataSource = filterItems;
    DropDownList2.DataBind();
}

Screenshot