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Editorial Team
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Asked: 2026-05-27T14:23:05+00:00

I am going through a ASP C# book and doing the tutorials. However I

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I am going through a ASP C# book and doing the tutorials. However I have encountered a problem. I have the following code that will list some events.

EventTracker.aspx 

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

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
 "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
  <title>Event Tracker</title>
  <style type="text/css">
      h1 
      {
          font-size: large;       
      }
  </style>
</head>
<body>
  <form id="Form1" runat="server">
    <div>       
      <h1>Controls being monitored for change events:</h1>
      <asp:TextBox ID="txt" runat="server" AutoPostBack="true"
       OnTextChanged="CtrlChanged" />
      <br /><br />
      <asp:CheckBox ID="chk" runat="server" AutoPostBack="true"
       OnCheckedChanged="CtrlChanged"/>
      <br /><br />
      <asp:RadioButton ID="opt1" runat="server" GroupName="Sample"
       AutoPostBack="true" OnCheckedChanged="CtrlChanged"/>
      <asp:RadioButton ID="opt2" runat="server" GroupName="Sample"
       AutoPostBack="true" OnCheckedChanged="CtrlChanged"/>
      <br /><br /><br /> 
       <h1>List of events:</h1>
      <asp:ListBox ID="lstEvents" runat="server" Width="355px"
       Height="305px" /><br />      
    </div>
  </form>
</body>
</html>

EventTracker.aspx.cs

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;

public partial class EventTracker : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        Log("<< Page_Load>>");

    }

    protected void Page_PreRender(object sender, EventArgs e)
    {
        //Find the control ID of the sender. 
        //This requires converting the Object type into a control class. 
        string ctrlName = ((Control)sender).ID;
        Log(ctrlName + " Changed");
    }

    protected void Log(string entry)
    {
        lstEvents.Items.Add(entry);

        //Select the last item to scroll the list so the most recent are visible
        lstEvents.SelectedIndex = lstEvents.Items.Count - 1;
    }
}

I am recieving the following error:

Error 1 ‘ASP.eventtracker_aspx’ does not contain a definition for
‘CtrlChanged’ and no extension method ‘CtrlChanged’ accepting a first
argument of type ‘ASP.eventtracker_aspx’ could be found (are you
missing a using directive or an assembly reference?)

I am new to ASP and would like to understand why such an error is occurring so in future reference I know what is causing it.

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1 Answer

  1. Editorial Team

    In your markup you have

    OnCheckedChanged="CtrlChanged"

    But there is no event handler with that name / matching signature in your codebehind…

    This event will be triggered everytime your CheckBox changes, but you do not have anything in the code that will respond.

    You need something like

    protected void CtrlChanged(object sender, EventArgs e)   
    {  // do something }
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