gridview后台控件获取问题

 现在想通过编辑仓库下拉框，带出所属库位信息。
再仓库选择的事件中，怎么取值和赋值？？？？
省略部分代码
 .
 .
 .<asp:TemplateField HeaderText="仓库">
                                    <ItemTemplate>
                                        <%# Eval("Warehouse_ID")%>
                                    </ItemTemplate>
                                    <EditItemTemplate>
                                        <asp:HiddenField ID="hck" runat="server" Value='<%# Eval("Warehouse_ID") %>' />
                                        <asp:DropDownList ID="DDLck" runat="server" style="width:80px" 
                                            AutoPostBack="True" onselectedindexchanged="DDLck_SelectedIndexChanged" />
                                    </EditItemTemplate>
                                     
                                </asp:TemplateField>
                                 <asp:TemplateField HeaderText="库位">
                                    <ItemTemplate>
                                        <%# Eval("Library_ID")%>
                                    </ItemTemplate>
                                    <EditItemTemplate>
                                        <asp:HiddenField ID="hkw" runat="server" Value='<%# Eval("Library_ID") %>' />
                                        <asp:DropDownList ID="DDLkw" runat="server" style="width:80px" />
                                    </EditItemTemplate>
                                     
                                </asp:TemplateField>                                                                     
                                        <asp:CommandField 
                                            ShowEditButton="True" CancelText="取消" DeleteText="删除" EditText="修改" 
                                            UpdateText="更新" ItemStyle-Width="80px"  >
<ItemStyle Width="80px" ForeColor="Black"></ItemStyle>
                                        </asp:CommandField>
                                    </Columns>
                                    <PagerSettings Visible="False" />
                                </asp:GridView>
后台：
 protected void DDLck_SelectedIndexChanged(object sender, EventArgs e)
        {
            //////库位加载
            //DropDownList ddlkw = (DropDownList)gv_InStoreList.HeaderRow.TemplateControl.FindControl("DDLck");
            //gv_InStoreList.
            ////DropDownList ddlck = (DropDownList)gv_InStoreList.TemplateControl.FindControl("DDLck");
            ////packageStorageBll.LoadPaLibrary(ddlkw, ddlck.SelectedValue);
        }