HiddenField Value property back to empty when "postback" using AJAX UpdatePanel

Question

I have been working with this issue for hours and cant find a solution. Now Im working in a web Application and my first problem was that I wanted to create an XML dynamically...Then I realized that after a postback, the Xml was resseting. Then I just though, "ok, lets create a HiddenField and keep storing nodes as string in the HiddenField value property, so at the end I just create a new XmlElement, create a document fragment with an InnerXml of the HiddenField.Value and attach the fragmentto the XmlElement"...But HiddenField.Value also RESETS every click on a button... I just tested this method with a label and IT WORKS...

Basically I have a page divided in two with the AJAXControlToolKit TabContainer Control. The first form is for the user main data while the second tab has a form that is intented to fill the form as many times as the user wants because its for storing family members. So the process is to fill a family member data, click the button and store it in the HiddenField.Value, fill the second family member data and click again to add a the new family member and concatenate to the HiddenField.Value...But I realized that after the first click on the Load Page method, the HiddenField.Value is again empty...

Maybe not that important but On the UpdatePanel there is just The button and a listbox to show some data of all the family members the user has saved, so the only object that refreshes on the click is the listbox.

As I just said, if instead using a HiddenField.Value I use a Label.Text, Everything Works...

<%@ Page Language="c#" MasterPageFile="/Plantilla.master" AutoEventWireup="true" Inherits="alta_personal_interno" %>
<%@ Register assembly="AjaxControlToolkit" namespace="AjaxControlToolkit" tagprefix="cc1" %>
<asp:Content runat="server" id="contentDefault" ContentPlaceHolderId="ContentPlaceHolderPagina">
<div align="left">
    <table style="width: 100%; background-color: maroon">
            <tbody>
                <tr>
                    <td>
                        <span id="ctl00_ContentPlaceHolder1_lblTitulo" class="EtiquetaMedianoBlanco">                                    
                        <asp:Label ID="lblTituloPExt" runat="server" Text="Alta de Personal Interno" />
                        </span>
                    </td>
                </tr>
            </tbody>
     </table>
</div>
<cc1:TabContainer runat="server">
    <cc1:TabPanel runat="server" HeaderText="Titular">
        <ContentTemplate>
            <--!Code with Form Elements-->
            <asp:Button ID="btnAgregarNvo" runat="server" Text="Guardar" onclick="btnAgregarNvo_Click"/>
        </ContentTemplate>    
    </cc1:TabPanel> 
     <cc1:TabPanel runat="server" HeaderText="Familia">
        <ContentTemplate>
            <asp:HiddenField runat="server" id="hidFamiliares"></asp:HiddenField>
            <!--Code with Form Elements-->
             <asp:UpdatePanel runat="server" id="upFamiliares">
                <ContentTemplate>
                    <asp:Button ID="btnAgregarFamiliar" runat="server" Text="Agregar" onclick="btnAgregarFamiliar_Click"/>
                    <asp:Button ID="btnQuitarFamiliar" runat="server" Text="Quitar" onclick="btnQuitarFamiliar_Click"/>
                    <br/>
                    <asp:ListBox runat="server" ID="lbFamiliares"/>
                </ContentTemplate>
            </asp:UpdatePanel>   
        </ContentTemplate>    
    </cc1:TabPanel> 
</cc1:TabContainer>

//------------------------------CODE BEHIND------------------------------------
private XmlDocument objXML;

protected void Page_Load(object sender, EventArgs e){
objXML = new XmlDocument();}

protected void btnAgregarFamiliar_Click(object sender, EventArgs e){
XmlElement xmlFamiliar = objXML.CreateElement("familiar");
AddAttribute("nombre",txtNombreF.Text,xmlFamiliar);
AddAttribute("apaterno",txtApF.Text,xmlFamiliar);
hidFamiliares.Value+=xmlFamiliar.InnerXml;}

private void AddAttribute(string name, string val, XmlElement parent){
XmlAttribute at = objXML.CreateAttribute(name);
at.Value = val;
parent.SetAttributeNode(at);}

Show us some code rather than describing it. – Brissles Jan 18 '12 at 18:06 — Brissles, Jan 18 '12 at 18:06

score 7 · Accepted Answer · answered Jan 18 '12 at 20:07

7

I'm unsure what's causing it, you might have to try a simpler scenario to troubleshoot.

If your method works with a Label control, you could always use an invisible one instead of a HiddenField?

<asp:Label runat="server" id="hidFamiliares" style="display:none;"/>

answered Jan 18 '12 at 20:07

Brissles

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This works just as I need...but Im still kind of confused why with the HiddenField doesnt work...there are no additinal lines between the two tests... – Symphonicmind Jan 18 '12 at 20:45
I had the same problem and you solution worked for me. I have to say that this is very odd. – Jean-Philippe Leclerc Sep 12 '13 at 19:19

score 1 · Answer 2 · answered Jan 18 '12 at 20:14

Bit of a guess.

But by the looks of the code, when you submit a button event within the UpdatePanel, it reloads the panel, but it doesn't reload the value of your HiddenField, so when the UpdatePanel content loads, it still sees the HiddenField as empty.

Wrapping the HiddenField in the same UpdatePanel might work. Or you could try wrapping it in it's own UpdatePanel then call UpdatePanel.Update() within your button event, making sure the UpdateMode is set to 'Conditional' on the panel.

I'll try this in a few secs...so the Text property of a label work different than the Value property of a HiddenField? — Symphonicmind, Jan 18 '12 at 20:20

HiddenField Value property back to empty when "postback" using AJAX UpdatePanel

2 Answers2