Bind value to cascading dropdown in datalist from code behind

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C#

ASP.NET

Hi All,
I have a cascading dropdownlist in a datalist .I need to assign the selectedvalue of cascading dropdown from code behind ie on another dropdownlist selected index changed.However I cant find the casacding dropdown in codebehind .Any help will be really appreciated.Thanks in advance.

What I have tried:

 <asp:DropDownList ID="ddl_eddriver" class="w3-input w3-border w3-round" Width="180px" runat="server" TabIndex="15"></asp:DropDownList> 
<asp:CascadingDropDown ID="CascadingDropDown5" runat="server"    Category="driver" TargetControlID="ddl_eddriver"  PromptText="[Select Driver]"    
LoadingText="Loading Driver's..."                                             ServicePath="~/Service/SSS.asmx"                          ServiceMethod="GetDropDownDrivers" Enabled="True">
</asp:CascadingDropDown>

 protected void ddl_editclnt_SelectedIndexChanged(object sender, EventArgs e)
        {
            DropDownList ddl_editclnt = sender as DropDownList;
            
            //get the namingcontainer from the dropdownlist and cast it as a datalistitem
            DataListItem item4 = ddl_editclnt.NamingContainer as DataListItem;
            objcon.GetReader("select IN021_01,ISNULL((select  IN002_01 FROM IN002_05 WHERE IN002_04.IN002_04_00=IN002_05.IN002_04_00),'') as driver from in021 inner join IN002_04 ON IN021.IN002_04_00=IN002_04.IN002_04_00  where IN021.IN021_01='" + ddl_editclnt.SelectedValue.ToString() + "'");
            if (objcon.dr.Read())
            {
                foreach (DataListItem item in this.DataList2.Items)
                {
                    DropDownList ddl_eddriver = item.FindControl("ddl_eddriver") as DropDownList;
                    
                    ddl_eddriver.SelectedValue = objcon.dr["driver"].ToString(); //I am getting error here
                    UpdatePanel2.Update();

                 }
                }
}