asp.net中ListBox在jQuery中遇到的问题——直接传值到不了后台

<%@ page title="" language="c#" masterpagefile="~/manager.master" codebehind="managersendmessage.aspx.cs" inherits="teacherfiles.managersendmessage" enableeventvalidation="false"%>

<asp:content id="content1" contentplaceholderid="head" runat="server">

</asp:content>

<asp:content id="content2" contentplaceholderid="contentplaceholdercontent" runat="server">

<script src="js/jquery-1.4.2.min.js" type="text/javascript"></script>

<script type="text/javascript">

        $(document).ready(function(){

             var lstboxallteachersid = "#"+'<%=lstboxallteachers.clientid%>';

             var lstboxselectdteachersid="#"+'<%=lstboxselectdteachers.clientid%>';

             var imabtnsendmessageid="#"+'<%=imabtnsendmessage.clientid%>';

             var hiddenfileid="#"+'<%=hiddenfield1.clientid%>';

             $('fieldset ul li img').click(function(){

                var options;

                var remove;

                // 把选择项追加给对方

                if($(this).attr("alt")=="arrowadd")

                {

                    options= $(lstboxallteachersid+" option:selected");                 

                    remove=options.remove();

                    remove.appendto(lstboxselectdteachersid);

                }

                // 把选择项退回给对方

                if($(this).attr("alt")=="arrowdelete")

                    options=$(lstboxselectdteachersid+" option:selected");

                    remove.appendto(lstboxallteachersid);

                // 把全部追加给对方

                if($(this).attr("alt")=="selectall")

                    options=$(lstboxallteachersid+' option');

                // 把全部项退回给对方

                if($(this).attr("alt")=="reset")

                    options=$(lstboxselectdteachersid+' option');

                }                                   

            });

            // 获取教师工号

           function getseletedteachernum()

            {

                var lststaffs = document.getelementbyid('<%=lstboxselectdteachers.clientid%>');

                var strstaffs = "";

                for (var i = 0; i < lststaffs.options.length; i++) {

                    strstaffs +=lststaffs.options[i].value+",";

                $(hiddenfileid).val(strstaffs);

            } 

            // 当点击发送按钮

            $(imabtnsendmessageid).click(function(){

                getseletedteachernum()

        });

    </script>

    <form>

<fieldset class="fieldset">

    <legend class="legend">选择需要得到通知的教师</legend>

    <ul>

        <li>

            <span>

                   <asp:listbox id="lstboxallteachers" runat="server"

                        cssclass="listbox"></asp:listbox>

            </span>

            <img src="images/arrowadd.jpg" alt="arrowadd" class="imagarrowadd" />

            <img src="images/arrowdelete.jpg" alt="arrowdelete" class="imagarrowdelete" />

            <span><asp:listbox id="lstboxselectdteachers" runat="server"

                      cssclass="listbox"></asp:listbox></span>

           <asp:hiddenfield id="hiddenfield1" runat="server"/>

        </li>

                <img src="images/selectall.jpg" alt="selectall" />

                <img src="images/reset.jpg" alt="reset" />

    </ul>

</fieldset>

<br />

    <legend class="legend">需要发送的消息</legend>

            <asp:textbox id="txtcontent" runat="server" textmode="multiline" width="380px"

                height="180px" cssclass="txtbox"></asp:textbox>

             <span>

                <asp:imagebutton id="imabtnsendmessage" runat="server"

                imageurl="~/images/sendmessage.jpg" onclick="imabtnsendmessage_click"/>

                <asp:imagebutton id="imagbtnresetcontent" runat="server"

                 imageurl="~/images/reset.jpg" onclick="imagbtnresetcontenet_click"/>

后台

 public partial class managersendmessage : basepage

    {

        iteacher newiteacher = new teacherservice();

        protected void page_load(object sender, eventargs e)

        {

            if (!ispostback)

                bindlistboxallteachers();

            }

        }

        public void bindlistboxallteachers()

            this.lstboxallteachers.datasource = newiteacher.readallteacher();

            this.lstboxallteachers.datatextfield = "teachername";

            this.lstboxallteachers.datavaluefield = "teachernum";

            this.lstboxallteachers.databind();

        list<string> allselectedteahcernum = new list<string>();

        // 得到选择的教师工号

        public void sendselectedteahcermessage(string[] singlenums)

            for (int i = 0; i < singlenums.count()-1; i++)

                newiteacher.insertreceivemessage(singlenums[i].tostring(), this.txtcontent.text);

                pageextension.alert(this, "发布成功！");

        // 发送通知消息给选定的教师,

        protected void imabtnsendmessage_click(object sender, imageclickeventargs e)

           string allthenum = this.hiddenfield1.value;

            string[] singlenums = allthenum.split(',');

            sendselectedteahcermessage(singlenums);

        // 重置发送内容

        protected void imagbtnresetcontenet_click(object sender, imageclickeventargs e)

            this.txtcontent.text = "";

    }