更新面板和脚本管理器不在ASP.NET中的级联下拉列表中工作

Question

我尝试在没有页面刷新的情况下填充下拉城市和区域。所以我在Updatepanel和Script Manager中使用。代码在

下面

  <asp:ScriptManager ID="script1" runat="server" EnablePartialRendering="true"></asp:ScriptManager>
            <div class="form-list wow fadeInRight" data-wow-delay="0.5s">

                    <ul class="navmain">


                        <li>
                           <asp:UpdatePanel ID="upd1" runat="server" UpdateMode="Conditional" ChildrenAsTriggers="true">
                               <ContentTemplate>


                            <!--<asp:DropDownList ID="drp_city" runat="server"   CssClass="drp" OnSelectedIndexChanged="drp_city_SelectedIndexChanged" AutoPostBack="true" ></asp:DropDownList>-->
                                <asp:DropDownList ID="drp_city1" runat="server" CssClass="drp" OnSelectedIndexChanged="drp_city_SelectedIndexChanged" AutoPostBack="true"></asp:DropDownList>


                            <asp:HiddenField ID="hfCustomerId" runat="server" />
                                   </ContentTemplate>
                           </asp:UpdatePanel>
                        </li>
                        <li>
                            <asp:UpdatePanel ID="upd2" runat="server" UpdateMode="Conditional">  
                               <ContentTemplate>
                            <asp:DropDownList ID="drp_area" runat="server"  CssClass="drp" AutoPostBack="true"></asp:DropDownList>
                                   </ContentTemplate>
                               <Triggers>
                                   <asp:AsyncPostBackTrigger ControlID="drp_city1" EventName="SelectedIndexChanged" />
                               </Triggers>
                            </asp:UpdatePanel>

                        </li>
                        <li>
                            <asp:UpdatePanel ID="upd3" runat="server">  
                               <ContentTemplate>
                            <asp:DropDownList ID="drp_cuisine" runat="server" CssClass="drp"></asp:DropDownList>
                            </ContentTemplate>

                                   </asp:UpdatePanel>
                        </li>

                        </ul>

                <asp:Button  OnClick="btn_search1" runat="server" CssClass="btn_search" />
            </div>

我无法找到错误。页面没有刷新，但区域下拉列表没有填充。