在javascript更新后，从web用户控件获取codebehind中的asp:TextBox文本属性

这是一个场景。

我有一个包含asp:PlaceHolder的简单页面。

<%@ Page Title="" Language="VB" MasterPageFile="~/MasterPage.master" AutoEventWireup="false" CodeFile="TrainingPlan.aspx.vb" Inherits="TrainingPlan" %>
<%@ Reference Control="ctlTask.ascx" %>
<%@ Reference Control="ctlTaskheader.ascx" %>
<asp:Content ID="Content1" ContentPlaceHolderID="MainContent" Runat="Server">
    <div class="centered">
        <h2><asp:Label ID="lblPlanTitle" runat="server" Text="Plan Title"></asp:Label></h2>
        <hr />
        <br />
        <asp:ImageButton ID="imgbtnSave" runat="server" ImageUrl="~/Images/save.ico" />
        <br />
        <asp:PlaceHolder ID="PlanPlaceHolder" runat="server"></asp:PlaceHolder>
    </div>
</asp:Content>

此页面上的占位符由同一web用户控件的几行填充。此web用户控件包含多个文本框。对于这个web用户控件中的每个文本框，我都有公共属性来设置和获取文本值。在web用户控件的页面加载事件中，我将向其中一些文本框添加onClick属性

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    txtTrainingStart.Attributes.Add("onClick", "txtTrainingStart_Click(" &  txtTrainingStart.ClientID & ", " & txtTask.ClientID & ");")
    txtTraineeBadgeNum.Attributes.Add("onClick", "txtTraineeBadgeNum_Click(" & txtTraineeBadgeNum.ClientID & ", " & txtTask.ClientID & ", " & txtTrainingStart.ClientID & ");")
    txtTrainerBadgeNum.Attributes.Add("onClick", "txtTrainerBadgeNum_Click(" & txtTrainerBadgeNum.ClientID & ", " & txtTrainingComplete.ClientID & ", " & txtTask.ClientID & ", " & txtTraineeBadgeNum.ClientID & ", " & Session.Item("isTrainer").ToString.ToLower & ");")
    txtDecertifyingOfficial.Attributes.Add("onClick", "txtDecertifyingOfficial_Click(" & txtDecertifyingOfficial.ClientID & ", " & txtTrainerBadgeNum.ClientID & ", " & txtTask.ClientID & ", " & Session.Item("isDecertifyingOfficial").ToString.ToLower & ");")
End Sub

对于每一个onClick事件，我都有相应的javascript函数。

<script type="text/javascript">
    function txtTrainingStart_Click(txtTrainingStart, txtTask) {
        //processing and updates to textboxes here
    }
</script>

问题来了。

在包含占位符的主页上，我有一个保存按钮。在保存按钮的单击事件中，我循环浏览占位符中包含的每个web用户控件，以处理和保存数据。

Protected Sub imgbtnSave_Click(sender As Object, e As ImageClickEventArgs) Handles imgbtnSave.Click
    For Each item As Control In PlanPlaceHolder.Controls
        Dim task As ctlTask = TryCast(item, ctlTask)
        If Not IsNothing(task) Then
            'need updated textbox values here. 
            'The following line gets the original textbox value, not the updated value that I need
            Dim test As String = task.trainingStart
        End If
    Next
End Sub

我所尝试的一切都只能得到页面加载时文本框中的原始值。我认为这应该很简单，我只是错过了一些基本的东西。我在谷歌上到处搜索这个解决方案，但我还没有找到。这是我发现的最接近的东西->Javascript PROPER方式中asp:label的Set Text属性。尽管这篇文章处理的是标签而不是文本框，并且没有使用包含几个web用户控件的占位符。据我所知，我需要将更新从客户端POST回服务器，但我不知道如何做到这一点。我尝试过使用Request.Form属性，但似乎无法实现。我错过了什么？

谢谢你的帮助，Rylan

编辑
以下是根据请求用web用户控件填充占位符的代码

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    Dim DBConn As MySqlConnection
    Dim cmd As New MySqlCommand
    DBConn = New MySqlConnection(Globals.mysqlConStr)
    Try
        lblPlanTitle.Text = Request.QueryString("plan_name") & " Training Plan"
        If Session.Item("empID") = -1 Then
            empID = clsUser.getID
        Else
            empID = Session.Item("empID")
        End If
        Dim strSQL As String = "SELECT * FROM task_revs tr WHERE tr.change != 'Deleted' and tr.id_plan = " & Request.QueryString("id_plan") & " ORDER BY task_num, rev_date desc"
        Dim da As New MySqlDataAdapter(strSQL, DBConn)
        Dim dtAllRevs As New DataTable
        da.Fill(dtAllRevs)
        Dim dtCurrentRev As New DataTable
        Dim lastTaskNum As String = ""
        dtCurrentRev = dtAllRevs.Clone
        For Each row As DataRow In dtAllRevs.Rows
            If lastTaskNum <> row("task_num") Then
                dtCurrentRev.ImportRow(row)
                lastTaskNum = row("task_num")
            End If
        Next
        strSQL = "SELECT * FROM checkoffs WHERE emp_id = " & empID
        da = New MySqlDataAdapter(strSQL, DBConn)
        Dim dtCheckoffs As New DataTable
        da.Fill(dtCheckoffs)
        Dim addColor As Boolean = True
        Dim tabWidth As Integer
        Dim Header As ctlTaskHeader = LoadControl("ctlTaskHeader.ascx")
        PlanPlaceHolder.Controls.Add(Header)
        For Each row As DataRow In dtCurrentRev.Rows
            Dim newRow As ctlTask = LoadControl("ctlTask.ascx")
            tabWidth = 0
            newRow.id_Task = row("id_Task")
            newRow.taskNum = row("task_num")
            newRow.task = row("task")
            If row("is_header") = True Then
                If row("task_num").ToString.EndsWith(".0") And row("task_num").ToString.Split(".").Count = 2 Then
                    newRow.taskBold = True
                    newRow.taskItalic = True
                Else
                    newRow.taskForeColor = Drawing.Color.Blue
                    newRow.taskItalic = True
                    tabWidth += 10
                End If
            Else
                tabWidth += 10
            End If
            For i As Integer = 0 To row("task_num").ToString.Split(".").Count - 3
                tabWidth += 10
            Next
            newRow.TabSize = tabWidth
            If Not IsDBNull(row("task_level")) Then
                For i As Integer = 0 To row("task_level") - 1
                    newRow.taskLevel = newRow.taskLevel & "*"
                Next
            End If
            If addColor = True Then
                newRow.taskNumBackColor = Drawing.Color.LightGray
                newRow.taskLevelBackColor = Drawing.Color.LightGray
                newRow.taskBackColor = Drawing.Color.LightGray
                newRow.trainingStartBackColor = Drawing.Color.LightGray
                newRow.trainingCompleteBackColor = Drawing.Color.LightGray
                newRow.traineeBadgeNumBackColor = Drawing.Color.LightGray
                newRow.trainerBadgeNumBackColor = Drawing.Color.LightGray
                newRow.decertifyingOfficialBackColor = Drawing.Color.LightGray
            End If
            addColor = Not addColor
            For Each checkoff As DataRow In dtCheckoffs.Rows
                If checkoff("id_task") = row("id_task") Then
                    If Not IsDBNull(checkoff("training_start")) Then
                        newRow.trainingStart = checkoff("training_start")
                    End If
                    If Not IsDBNull(checkoff("training_complete")) Then
                        newRow.trainingComplete = checkoff("training_complete")
                    End If
                    If Not IsDBNull(checkoff("trainee_badge")) Then
                        newRow.traineeBadgeNum = checkoff("trainee_badge")
                    End If
                    If Not IsDBNull(checkoff("trainer_badge")) Then
                        newRow.trainerBadgeNum = checkoff("trainer_badge")
                    End If
                    If Not IsDBNull(checkoff("decertifying_official")) Then
                        newRow.decertifyingOfficial = checkoff("decertifying_official")
                        newRow.taskNumBackColor = Drawing.Color.LightSalmon
                        newRow.taskLevelBackColor = Drawing.Color.LightSalmon
                        newRow.taskBackColor = Drawing.Color.LightSalmon
                        newRow.trainingStartBackColor = Drawing.Color.LightSalmon
                        newRow.trainingCompleteBackColor = Drawing.Color.LightSalmon
                        newRow.traineeBadgeNumBackColor = Drawing.Color.LightSalmon
                        newRow.trainerBadgeNumBackColor = Drawing.Color.LightSalmon
                        newRow.decertifyingOfficialBackColor = Drawing.Color.LightSalmon
                    End If
                End If
            Next
            If row("is_header") = True And PlanPlaceHolder.Controls.Count > 1 Then
                Dim newLine As LiteralControl = New LiteralControl("<br/>")
                PlanPlaceHolder.Controls.Add(newLine)
            End If
            PlanPlaceHolder.Controls.Add(newRow)
        Next
    Catch ex As Exception
        clsLog.logError(ex)
    Finally
        DBConn.Close()
    End Try

编辑2
我认为展示我如何更新javascript函数中的文本框可能也很重要

    function txtTrainingStart_Click(txtTrainingStart, txtTask) {
                var currentdate = new Date();
                var datetime = (currentdate.getMonth() + 1) + "/" + currentdate.getDate() + "/" + currentdate.getFullYear() + " " + getTimeAMPM();
                txtTrainingStart.value = datetime;
                txtTrainingStart.style.backgroundColor = "yellow";
    }