c# - asp.net Label cannot ever be modified from code-behind -

i have panel/updatepanel contains asp.net label. seems under no circumstances whatsoever text field of control can changed. code:

    <asp:panel runat="server" id="panel1" width="100%">     <asp:updatepanel runat="server" id="updroutegroup" updatemode="conditional">       <triggers>         <asp:postbacktrigger controlid="btndisableonhold" />       </triggers>       <contenttemplate>                <asp:panel id="pnlimpexcel" runat="server" >       <div style="width:100%">        <table colspan="0" width="100%" cellpadding="0" cellspacing="0">           <tr>              <th colspan="3">                 on hold music              </th>           </tr>           <tr style="height:10px"></tr>           <tr>              <td align="left" valign="middle" style="width:33%"><div id="fine-uploader"></div></td>              <td align="center" valign="middle"><asp:label id="lblonholdfile" runat="server" text="current file: none" /></td>              <td align="right" valign="middle"><asp:button id="btndisableonhold" runat="server" style="margin-right:7px;width:87px;" text="disable hold music" cssclass="button" onclick="btndisableonhold_onclick" /></td>           </tr>           <tr><td colspan ="2" align="center"><asp:label runat="server" id="lbluploaderror" style="color: red;" visible="false" /></td></tr>        </table>                      </div>        </asp:panel>         </contenttemplate>      </asp:updatepanel>      </asp:panel> 

when postback occurs might need update this, check conditions , attempt modify text doing:

protected void page_load(object sender, eventargs e) {     if (this.page.ispostback)        lblonholdfile.text = "some text."; } 

this code bad, i've little experience asp.net , have inherited project. still cannot understand point of exposing these labels in code-behind if cannot modify them @ all. how can set .text field of control lblonholdfile? thanks.

here what's in btndisablehold_onclick:

  protected void btndisableonhold_onclick(object sender, eventargs e)   {      //update records       // clear out existing file label:      lblonholdfile.text = "current file: none";   } 

that problem, line:

lblonholdfile.text = "current file: none"; 

you have undone text change made in page_load above line in click event handler.

the text property of label got changed twice; once some text in page_load , original value in btndisableonhold_onclick method. makes appear setting text value nothing, when in reality changed.

update:

to have javascript create postback code, need invoke __dopostback function.

read understanding javascript __dopostback function