Label control throws system.nullreferenceexception

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I am new to ASP.Net and stuck with my First program itself. My label is throwing the following Exception :(

System.NullReferenceException: 'The object reference was not set to an object instance.'

)

My designer page has the Label as follows:-

protected global::System.Web.UI.WebControls.Label lblmsg;

Could someone help me, where I am going wrong.

What I have tried:

Here is my firstpage.aspx

ASP.NET

<pre><%@ Page Language="C#" AutoEventWireup="true" CodeBehind="FirstPage.aspx.cs" Inherits="WebApplicationDemo.FirstPage" %>
<!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>
</head>
<body>
    <form id="form1" runat="server">
        <div>
            <%Response.Write("HeLLo World"); %>
             <asp:label ID="lblmsg" runat="server"/>
            <asp:Button Text="Go to Second Page" runat="server" OnClick="BtnGOTOSECOND_Click"/>
        </div>
    </form>
</body>
</html>

Here is my firstpage.aspx.cs

C#

<pre>using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.OleDb;
using System.Data;

namespace WebApplicationDemo
{
    public partial class FirstPage : System.Web.UI.Page
    {
        public FirstPage()
        {
            
            lblmsg.Text = "My First Label";
           
                   
        }
      
        protected void BtnGOTOSECOND_Click(object sender, System.EventArgs e)
        {
            Response.Redirect("SecondPage.aspx");
        }
    }
}

Posted 25-May-19 18:29pm

Priya Karthish

Updated 29-May-19 6:45am

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3 solutions

Solution 2

You're trying to access the control from the constructor. The control tree has not been created at that point.

The absolute earliest point you can access the controls is after the base FrameworkInitialize method has been invoked:

C#

protected override void FrameworkInitialize()
{
    base.FrameworkInitialize();
    
    // The control tree has now been created.
}

This typically happens just before the Init event, so that's usually the best place for this sort of code.

Posted 29-May-19 6:45am

Richard Deeming

Solution 3

were you able to solve this, if I initialize as the solution suggest text is not appearing actually

Posted 8hrs 10mins ago

Member 16393268

Comments

Richard Deeming 8hrs ago

"Me too" is not a solution to anyone's question.

The accepted solution is somewhat wrong; it creates a new label, sets the text, and then throws it away.

You need to use the control created by the markup. But as the other solution explains, you can't do that before the FrameworkInitialize method has been called.

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Gerry Schmitz · Accepted Answer · 2019-05-25T18:36:00

Solution 1

lblmsg = new Label();
lblmsg.Text = "My First Label";

Posted 25-May-19 18:36pm

Gerry Schmitz