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Asked: 2026-05-20T18:47:21+00:00

I’ve a ASP.Net page (Default.aspx) which will load UserControl (ucontrol.ascx) dynamically into an UpdatePanel.

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I’ve a ASP.Net page (Default.aspx) which will load UserControl (ucontrol.ascx) dynamically into an UpdatePanel. By using UpdatePanel, we believe we’re able to prevent the entire page to be posted-back.

My problem is, within the UserControl, we have some form controls, such as inputs and buttons; after the UserControl is loaded, clicking on any button inside the UserControl will cause the UpdatePanel to be blanked. During the investigation, I found that, breakpoints within the Button1_Click() in the code-behind for the UserControl is never reached. Please reference to the code below, this references to [REFERENCE]1. It’s an urgent task, please kindly help.

Thanks!
William

Default.aspx:

<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %>

<!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>Untitled Page</title>
</head>
<body>
    <form id="form1" runat="server">
        <asp:ScriptManager ID="ScriptManager1" runat="server" EnablePartialRendering="true">
        </asp:ScriptManager>

        <asp:UpdatePanel ID="UpdatePanel1" runat="server">
            <ContentTemplate>
                <span>This is hosting page</span><br />
                <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Add UserControl" />
            </ContentTemplate>
            <Triggers>
                <asp:AsyncPostBackTrigger ControlID="Button1" />
            </Triggers>
        </asp:UpdatePanel>

        <asp:UpdatePanel ID="UpdatePanel2" runat="server" UpdateMode="Conditional">
            <ContentTemplate>
                <asp:PlaceHolder ID="PartHolder" runat="server">
                </asp:PlaceHolder>
            </ContentTemplate>
            <Triggers>
                <asp:AsyncPostBackTrigger ControlID="Button1" />
            </Triggers>
        </asp:UpdatePanel>

     </form>
</body>
</html>

Default.aspx.cs:

using System;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;

public partial class _Default : System.Web.UI.Page 
{

    protected void Page_Load(object sender, EventArgs e)
    {
    }

    protected void Button1_Click(object sender, EventArgs e)
    {
        loadparts();
    }

    private void loadparts(){
        Control formpart =  LoadControl("ucontrol.ascx");
        formpart.ID = "formpart";
        PartHolder.Controls.Add(formpart);
    }
}

ucontrol.ascx:

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="ucontrol.ascx.cs" Inherits="ucontrol" %>

        <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
        &nbsp;This is Web User Control in UpdatePanel<br />
        &nbsp;<br />
        &nbsp;<br />
        <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        <asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click"/>

ucontrol.ascx.cs:

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;

public partial class ucontrol : System.Web.UI.UserControl
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        Label1.Text = TextBox1.Text;
        TextBox1.Text = "";
        TextBox1.Focus();
    }
}
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1 Answer

  1. Editorial Team

    Here’s what’s happening:

    1. First page load. No user control on page.
    2. Person clicks Button1 on the page.
    3. Page posts back (update panels do a full postback behind the scenes) and your Button1_Click handler on the page is run, which loads the user control into the page.
    4. User now sees the user control and clicks ITS Button1.
    5. Page posts back, but this time the Button1_Click handler on the page is not run (different button was clicked, even though you named them the same). Which means that loadparts() is not called and the user control is NOT loaded into the control tree.
    6. Your Button1_Click handler in the user control is not run because the user control is not around to see that the button was clicked.

    What you need to do is ensure that the user control is loaded into the page’s control tree, even when you click the user control’s button. That’s why Andrew suggested you put the loadparts() into the Page_Load event. I can see that doesn’t fit with the flow of your page, so you’ll have to find another way to load it at the correct times.

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