radgrid editformsetting control event

Hi ,

I am new to this radgrid . Need some help from anyone who has faced this issue. In the EditFormSetting in the radgrid i have two raddropdownlist. The functionality that i need is ..on selectionindexchange of the first dropdownlist,the contents of second dropdownlist need to be populated from a datasource. How do i achieve this? The problem i am facing is i am not able to access the dropdownlist control in the selectionchanged event of the first dropdownlist.

  <EditFormSettings EditFormType="Template">
                    <FormTemplate>
                        <table style="width: 500px">
                          <tr>
                                <td>
                                    <asp:Label ID="Label1" runat="server" Text="lblDropdown1:" Visible="true"></asp:Label>
                                </td>
                                <td class="tableCellRight" style="width: 85%">
                                    <asp:DropDownList ID="rd_Dropdown1" runat="server" AppendDataBoundItems="True" AutoPostBack="True"   Visible="true" OnSelectedIndexChanged="rd_Dropdown1_SelectedIndexChanged" DataSourceID="ds_dropdown1" DataTextField="field2" DataValueField="field1">
                                        <Items>
                                            <asp:ListItem runat="server" Text="--Select item--" Value="NA" />
                                             
                                            
                                        </Items>
                                    </asp:DropDownList>
                                </td>
                            </tr>
                            <tr>
                                <td>
                                    <asp:Label ID="Label2" runat="server" Text="lbldropdown2:" Visible="False"></asp:Label>
                                </td>
                                <td class="tableCellRight" style="width: 85%">
                                   <telerik:RadDropDownList ID="rd_dropdown2" runat="server" AppendDataBoundItems="True" AutoPostBack="True" DataSourceID="ds_dropdown2"  DataTextField="field2" DataValueField="field1"  Visible="False">
                                        <Items>
                                            <telerik:DropDownListItem runat="server" Text="--Select names--" Value="N/A" />
                                            
                                        </Items>
                                    </telerik:RadDropDownList> 
                                </td>
                            </tr>
                            
                        </table>
                    </FormTemplate>
                </EditFormSettings>

 <asp:SqlDataSource ID="ds_dropdown1" runat="server" ConnectionString="<%$ ConnectionStrings:xxConnectionString%>" SelectCommand="SELECT field1, field2 FROM [table1] ">
                   </asp:SqlDataSource>

 <asp:SqlDataSource ID="ds_dropdown2" runat="server" ConnectionString="<%$ ConnectionStrings:xxConnectionString %>" SelectCommand="SELECT [field1], [field2] FROM [table1] WHERE (somecondition)">          
        </asp:SqlDataSource>

codebehindfile event code

 protected void rd_Dropdown1_SelectedIndexChanged(object sender,EventArgs e)
    {
       //what code is required here to fetch or access dropdown2 control so that i bind it with suitable sqlcommand?


   
        //RadGrid1.DataBind();
    }