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Asked: 2026-06-07T21:59:07+00:00

I have an ASP.Net Update Panel which contains controls that I am trying to

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I have an ASP.Net Update Panel which contains controls that I am trying to update from the code-behind file by setting the value of the controls to whatever I want them to be, and then calling the Update() method of the UpdatePanel.

I know that to call the Update() method, I need to set the UpdateMode property to conditional so this is what I have done, but I am getting the following error regardless:

The Update method can only be called on UpdatePanel with ID ‘UpdatePanel1’ when UpdateMode is set to Conditional.

My Properties box looks like this:

Properties

My code looks like this:

using System;
using System.Timers;

namespace WebApplication2
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            var myTimer = new System.Timers.Timer();
            myTimer.Interval = 1000;

            myTimer.Elapsed += new ElapsedEventHandler(myTimer_Elapsed);

            myTimer.Start();
        }

        void myTimer_Elapsed(object sender, ElapsedEventArgs e)
        {
            var newGUID = Guid.NewGuid().ToString();
            Label1.Text = newGUID;
            UpdatePanel1.Update();
        }
    }
}

My form looks like this:

My ASPX Form

My Markup is below:

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="WebApplication2.WebForm1" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <style type="text/css">
        #form1
        {
            text-align: center;
        }
    </style>
</head>
<body>
    <form id="form1" runat="server">
    <asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>
    <asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
        <ContentTemplate>
            <asp:Label ID="Label1" runat="server" style="text-align: center" Text="Label"></asp:Label>
        </ContentTemplate>
    </asp:UpdatePanel>
    </form>
</body>
</html>

Why isn’t this working?

Thanks

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1 Answer

  1. Editorial Team

    I would recommend you checking the following tutorial. The Timer control used is a System.Web.UI.Timer and not a System.Timers.Timer as in your code. Also the timer must be placed inside the update panel in order for it to trigger an AJAX call when the OnTick event is triggered:

    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<%@ Page Language="C#" %>
<html dir="ltr" xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title></title>
    <script runat="server" type="text/c#">
    protected void Timer1_Tick(object sender, EventArgs e)
    {
        Label1.Text = "Panel refreshed at: " + DateTime.Now.ToLongTimeString();
    }
</script>
</head>
<body>
    <form id="form1" runat="server">
        <asp:ScriptManager runat="server" id="ScriptManager1" />

        <asp:UpdatePanel runat="server" id="UpdatePanel1">
        <ContentTemplate>
            <asp:Timer runat="server" id="Timer1" Interval="1000" OnTick="Timer1_Tick" />
            <asp:Label runat="server" Text="Page not refreshed yet." id="Label1" />
        </ContentTemplate>
        </asp:UpdatePanel>

        <asp:Label runat="server" Text="Label" id="Label2"></asp:Label>
    </form>
</body>
</html>
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