jquery UI对话框中使用的Asp.net控件值在代码后面是空的

我正在做一个asp.net应用程序。我使用Jquery UI向数据库添加记录。这是标记。

 <div id="AddShippingPopup" class="popup" title="New Shipping Address">
        <p>Shipping Address</p>
         <table>
               <tr>
                    <td> Line 1:</td>
                    <td><asp:TextBox ID="txtShippingLine1" runat="server"></asp:TextBox></td>
                    </tr>
                    <tr>
                    <td>Line 2:</td>
                    <td><asp:TextBox ID="txtShippingLine2" runat="server"></asp:TextBox></td>
                    </tr>
                    <tr>
                    <td>City:</td>
                    <td> <asp:TextBox ID="txtShippingCity" runat="server"></asp:TextBox></td>
                    </tr>
                    <tr>
                    <td>State:</td>
                    <td> <asp:DropDownList ID="ddlShipingState" runat="server" Width="200px" CssClass="required">
                        <asp:ListItem Value="">Please select</asp:ListItem>
                        <asp:ListItem Value="AK">Alaska</asp:ListItem>
                    </asp:DropDownList></td>
                    </tr>
                    <tr>
                    <td>Zip:</td>
                    <td><asp:TextBox ID="txtShippingZip" runat="server" Width="50px"></asp:TextBox></td>
                    </tr>  
                <tr>
                    <td>Preferred:</td>
                    <td>
                        <asp:CheckBox ID="chkPreferredShipAdd" runat="server" />
                    </td>
                    </tr>  
         </table>
    </div>

在这个div之外有一个按钮:

 <asp:Button ID="btnAddShipping" runat="server" Text="Add Shipping" style = "display:none" OnClick = "btnAddShipping_Click" />

和Jquery对话框代码:

     $("#AddShippingPopup").dialog({
                 autoOpen: false,
                 modal: true,
                 width: 500,
                 height: 370,
                 buttons: {
                     "Cancel": function () {
                         $(this).dialog("close");
                     },
                     "Save": function () {
                         $("[id*=btnAddShipping]").click();
                         $(this).dialog("close");
                     }
                 }
             });

function createShippingAddress() {
         $("#AddShippingPopup").dialog("widget").find(".ui-dialog-titlebar-close").hide();
         $("#AddShippingPopup").dialog("open");
         return false;
     }

，这里是初始化对话框的链接:

   <asp:LinkButton ID="lnkAddNewShippingAddress" runat="server" Font-Size="Smaller" OnClientClick="createShippingAddress(); return false;">Add New</asp:LinkButton>

，但当单击Save按钮时，文本框和下拉框的值为空。空字符串保存在db中。