error: System.NullReference Exception: Object reference not set

[yogarajan]

hi

i had developed pop3 Account mail view in my web page

but i got error in (System.NullRef erence Exception: Object reference not set)
NetStrm.Write(s zData, 0, szData.Length); - this line

///my code start here (cs file)
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Net;
using System.Net.Sockets;
using System.IO;

public partial class _Default : System.Web.UI.Page 
{
    public TcpClient testServername;
    public NetworkStream NetStrm;
    public StreamReader RdStrm;
    public string Data;
    public byte[] szData;
    public string CRLF = "\r\n";	
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        string strpopservername = txtpopservername.Text;
        string strusername = txtusername.Text;
        string strpassword = txtpassword.Text;
        
        //Cursor cr = Cursor.Current;
        //Cursor.Current = Cursors.WaitCursor;

        testServername = new TcpClient(strpopservername, 110);
        //Status.Items.Clear();

        try
        {
            // initialization
            NetStrm = testServername.GetStream();
            RdStrm = new StreamReader(testServername.GetStream());
            //Status.Items.Add(RdStrm.ReadLine());
            //Label1.Text = Label1.Text + RdStrm.ReadLine();
            ListBox1.Items.Add(RdStrm.ReadLine());

            // Login Process
            Data = "USER " + strusername + CRLF;
            szData = System.Text.Encoding.ASCII.GetBytes(Data.ToCharArray());
            NetStrm.Write(szData, 0, szData.Length);
            //Status.Items.Add(RdStrm.ReadLine());
            //Label1.Text = Label1.Text + RdStrm.ReadLine();
            ListBox1.Items.Add(RdStrm.ReadLine());

            Data = "PASS " + strpassword + CRLF;
            szData = System.Text.Encoding.ASCII.GetBytes(Data.ToCharArray());
            NetStrm.Write(szData, 0, szData.Length);
            //Status.Items.Add(RdStrm.ReadLine());
            //Label1.Text = Label1.Text + RdStrm.ReadLine();
            ListBox1.Items.Add(RdStrm.ReadLine());


            // Send STAT command to get information ie: number of mail and size
            Data = "STAT" + CRLF;
            szData = System.Text.Encoding.ASCII.GetBytes(Data.ToCharArray());
            NetStrm.Write(szData, 0, szData.Length);
            //Status.Items.Add(RdStrm.ReadLine());
            //Label1.Text = Label1.Text + RdStrm.ReadLine();
            ListBox1.Items.Add(RdStrm.ReadLine());


            // change enabled - disabled button
            Butconnect.Enabled = false;
            Butdisconnect.Enabled = true;
            ButRetrieve.Enabled = true;
            //ConnectBtn.Enabled = false;
           // DisconnectBtn.Enabled = true;
           // RetrieveBtn.Enabled = true;

            // back to normal cursor
            //Cursor.Current = cr;

        }
        catch (InvalidOperationException err)
        {
            //Status.Items.Add("Error: " + err.ToString());
            //Label1.Text = "Error: " + err.ToString();
            ListBox1.Items.Add("Error: " + err.ToString());
        }

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

    }
    protected void ButRetrieve_Click(object sender, EventArgs e)
    {
        // change cursor into wait cursor
        //Cursor cr = Cursor.Current;
        //Cursor.Current = Cursors.WaitCursor;
        string szTemp;
        //Message.Clear();
        Label2.Text = "";
        try
        {
            // retrieve mail with number mail parameter
            Data = "RETR " + txtnumber.Text + CRLF;
            szData = System.Text.Encoding.ASCII.GetBytes(Data.ToCharArray());
            //NetStrm.Write(szData, 0, szData.Length);
            NetStrm.Write(szData, 0, szData.Length);

            szTemp = RdStrm.ReadLine();
            if (szTemp[0] != '-')
            {

                while (szTemp != ".")
                {
                    Label2.Text += szTemp + CRLF;
                    szTemp = RdStrm.ReadLine();
                }
            }
            else
            {
                ListBox1.Items.Add(szTemp);
            }

            // back to normal cursor
            //Cursor.Current = cr;

        }
        catch (InvalidOperationException err)
        {
            ListBox1.Items.Add("Error: " + err.ToString());
        }
        catch (System.Exception ex)
        {
            ListBox1.Items.Add("Error : " + ex.ToString());
        }

    }
}

///my code end here

pls guide me

Thanks

[Plater]

Wouldn't you need to Connect() your TcpClient before trying to write data to it?

[yogarajan]

hi

thanks for ur reply

can u send code

pls

thanks

Wouldn't you need to Connect() your TcpClient before trying to write data to it?

[Plater]

hi

thanks for ur reply

can u send code

pls

thanks

...

testServername. Connect()

[r035198x]

hi

thanks for ur reply

can u send code

pls

thanks

NullReferenceEx ception simply means that you tried to dereference a null. In that line you are dereferencing two objects. NetStr and szData. If you do a Console.WriteLi ne of those variables before the call you will see which one is null.