System.NullReferenceException

Question

Hello guys

i got this error after i executed a bill update
here is the code underlined

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace NSPM_Sales_Invoice
{
static class Program
{
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Login());
}
}
}

please what could have gone wrong?

Amit Gupta · Answer

You are getting exception in constructor class, as your login code is written on button click, so the issue is with designer part, if you have took any reference image or control which is not present then you should re-check that part. However sometimes clean and rebuild your project works as a solution too.

Salman Beg · Answer

System.NullReferenceException means somewhere the object is null and you are trying to use that object. And in your case goto Login () and check where you are getting null and try to resolve it and after that your problem will be solved. Follow this video for an example, https://youtu.be/GwtevbSLuXQ

Laxmidhar Sahoo · Answer

hi Problem is in desiner , may a object(control is not instatiated) initializecomponent();

Salman Beg · Answer

Did you debug the code and in which line it is coming null? Thanks

Chidiebere Mgbemena · Answer

Login codes namespace NSPM_Sales_Invoice { public partial class Login : Form { public Login() { InitializeComponent(); } private void Login_Load( object sender, EventArgs e) { } private void btnLogin_Click( object sender, EventArgs e) { SqlConnection sqlcon = new SqlConnection(@ "Data Source=Chidiebere;Initial Catalog=NSPM_Sales_Invoice_DB;Integrated Security=True" ); String query = "Select * from tbl_Login Where username = '" + txtUserName.Text.Trim() + "' and password = '" + txtPassword.Text.Trim() + "'" ; SqlDataAdapter sda = new SqlDataAdapter(query, sqlcon); DataTable dtbl = new DataTable(); sda.Fill(dtbl); if (dtbl.Rows.Count == 1) { Dashboard objDashboard = new Dashboard(); this .Hide(); objDashboard.Show(); } else { MessageBox.Show( "Check your Username and Password" ); } } private void btnExit_Click( object sender, EventArgs e) { this .Close(); } } } using System; using System.Collections.Generic; using System.Linq; using System.Threading.Tasks; using System.Windows.Forms; namespace NSPM_Sales_Invoice { static class Program { /// /// The main entry point for the application. /// [STAThread] static void Main() { Application.EnableVisualStyles(); Application.SetCompatibleTextRenderingDefault( false ); Application.Run( new Login()); } } }

Laxmidhar Sahoo · Answer

hi @Salaman is currect .if still not working display login class

Salman Beg · Answer

Is it working now?

Chidiebere Mgbemena · Answer

Thanks

System.NullReferenceException

Answers (8)