用TemplateField自定义的DropDownList在后台如何取值

我在GridView中声明了一个TemplateField，在后台cs想取它的DropDownList值如何写这块，请帮帮我这个新人，谢谢！！！！
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False"
            DataKeyNames="ST_User_id"  AllowPaging="True" AllowSorting="True" Width="424px" OnRowEditing="Gridview1_RowEditing" OnPageIndexChanging="GridView1_PageIndexChanging" OnRowCancelingEdit="GridView1_RowCancelingEdit" OnRowUpdating="GridView1_RowUpdating" OnRowDeleting="GridView1_RowDeleting">
            <Columns>
                <asp:BoundField DataField="ST_User_id" HeaderText="用户编号" ReadOnly="True" SortExpression="ST_User_id" />
                <asp:BoundField DataField="ST_Teacher_name" HeaderText="姓名" SortExpression="ST_Teacher_name" />
                <asp:TemplateField HeaderText="用户类型" SortExpression="ST_User_power">
                    <EditItemTemplate>
                       <asp:DropDownList ID="st_ddl_users" SelectedIndex='<%#DataBinder.Eval(Container.DataItem,"ST_User_power").ToString().Equals("0")?0:1 %>' runat="server">
                          <asp:ListItem>普通学生</asp:ListItem>
                          <asp:ListItem>管理员</asp:ListItem>
                          </asp:DropDownList>
                         </EditItemTemplate>
                    <ItemTemplate>
                        <asp:Label ID="Label1" runat="server" Text='<%#DataBinder.Eval(Container.DataItem,"ST_User_power").ToString().Equals("0")?"普通学生":"管理员" %>'></asp:Label>
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:CommandField ShowEditButton="True" />
               <asp:TemplateField ShowHeader="False">
             <ItemTemplate>
             <asp:LinkButton ID="LinkButton1" runat="server" CausesValidation="False" CommandName="Delete"
             OnClientClick='return confirm("确认删除吗?");' Text="删除" />
            </ItemTemplate>
            </asp:TemplateField>
            </Columns>
        </asp:GridView>
cs中
st_comm.Parameters.Add(new SqlParameter("@user_power", SqlDbType.Int, 4));
                 st_comm.Parameters["@user_power"].Value = ?????
--------------------编程问答-------------------- 顶 --------------------编程问答-------------------- 你在哪个事件里执行
st_comm.Parameters.Add(new   SqlParameter( "@user_power ",   SqlDbType.Int,   4));
                                  st_comm.Parameters[ "@user_power "].Value   =   ?????

这句语句？

补充：.NET技术 ,  ASP.NET