System.NullReferenceException: Object reference not set to an instance of an object.

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hi friends,
I have the following exception System.NullReferenceException: Object reference not set to an instance of an object.I Am crating an application for online exam.Plz help me.Here is my code

C#

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 QuestionPaper : System.Web.UI.Page
{
    OnlineExamsDataContext _mycontext = new OnlineExamsDataContext();
    string myname;
    int rowIncre = 0;

    protected void Page_Load(object sender, EventArgs e)
    {
        myname = Request.QueryString["uname"].ToString();
        lbluname.Text = "Hi..." + myname;
        Random myrandom = new Random();
        Int64 temp = 0;
        ArrayList ar = new ArrayList();
        if (!IsPostBack)
        {
            for (int i = 0; ar.Count < 20; i++)
            {
                temp = myrandom.Next(1, GridView3.Rows.Count);
                if (!ar.Contains(temp))
                {
                    ar.Add(temp);
                }
            }
            GridView1.DataSource = ar;
            GridView1.DataBind();
            SelectMyQuestion(Convert.ToInt32(GridView1.Rows[0].Cells[0].Text));
        }


    }

     private void SelectMyQuestion(int Quesnumber)
    {
        lable6.Text = Quesnumber.ToString();
        GridView2.DataSource = SqlDataSource1;
        GridView2.DataBind();
        RbtnLAns.Items.Clear();
        lblmyques.Text = GridView2.Rows[0].Cells[1].Text.ToString();
        RbtnLAns.Items.Add(GridView2.Rows[0].Cells[2].Text.ToString());
        RbtnLAns.Items.Add(GridView2.Rows[0].Cells[3].Text.ToString());
        RbtnLAns.Items.Add(GridView2.Rows[0].Cells[4].Text.ToString());
        RbtnLAns.Items.Add(GridView2.Rows[0].Cells[5].Text.ToString());
        lable8.Text = GridView2.Rows[0].Cells[6].Text.ToString();
    }
    int result;
    protected void BtnAns_Click(object sender, EventArgs e)
    {
        if (ViewState["Result"] == null) 
        {
            for (int i = 0; i < RbtnLAns.Items.Count; i++)
            {
                if (RbtnLAns.Items[i].Selected == true)
                {
                    if (RbtnLAns.Items[i].Text.ToString() == lable8.Text)
                        result = 1;
                    else
                        result = 0;
                }
            }
        }
        else
        {
            for (int i = 0; i < RbtnLAns.Items.Count; i++)
            {
                if (RbtnLAns.Items[i].Selected == true)
                {
                    if (RbtnLAns.Items[i].Text.ToString() == lable8.Text)
                        result = Convert.ToInt32(ViewState["Result"]) + 1;
                    else
                        result = Convert.ToInt32(ViewState["Result"]);
                }
            }
        }
        ViewState["Result"] = result;
        lable9.Text = ViewState["Result"].ToString();

        int CountQues = GridView1.Rows.Count;
        if (ViewState["QuesNo"] == null)
        {
            rowIncre++;
            SelectMyQuestion(Convert.ToInt32(GridView1.Rows[rowIncre].Cells[0].Text));
            ViewState["QuesNo"] = rowIncre.ToString();
        }
        else
        {
            rowIncre = Convert.ToInt32(ViewState["QuesNo"]) + 1;

            if (rowIncre == 20)
            {
                Response.Redirect("Result.aspx?result=" + ViewState["Result"].ToString() + "&Myname=" + myname + "&examid=" + Request.QueryString["examid"]);
            }

            SelectMyQuestion(Convert.ToInt32(GridView1.Rows[rowIncre].Cells[0].Text));
        }
        ViewState["QuesNo"] = rowIncre.ToString();
        int MyQuNo = Convert.ToInt32(ViewState["QuesNo"]);
    }
}

Posted 2-Oct-13 19:12pm

Member 10312257

Updated 2-Oct-13 19:15pm

Thanks7872

v2

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Comments

Thanks7872 3-Oct-13 1:16am

We are not smart enough to guess the line on which error occurred.

_Damian S_ 3-Oct-13 1:17am

Don't be shy... feel free to narrow down the line that you are receiving the error on...

Member 10312257 3-Oct-13 1:24am

hey friends...its the qurstion paper code...for generating random questions...and after that it has the examresult page...when i run the application itz getting updated in the database but showing error after the instruction page i.e the quuestion paper part.!
Friends pls help....ASAP

Member 10312257 3-Oct-13 1:26am

I Guess The reason is that the program is trying to access a member of a reference type variable which is set to null....but am not able to identify the line that am receiving the error

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**Azee** · Answer 1 · 2013-10-02T19:34:00

Hey there,

Since you haven't mentioned at which line you are getting this exception (you can try debugging and find out), so after looking at your code, I think it could be one of these problems:

If the Exception is coming when the page is loaded it could be either this line:

C#

myname = Request.QueryString["uname"].ToString();

if the your page is not getting uname QuertString, then ToString() will cause that Exception.

Or

It could be any of the lines containing this type of statement:

C#

GridView1.Rows[0].Cells[0].Text

You should check whether the GridView contains atleast one row before executing any line like this because if it doesn't Rows[0] can cause that exception, use:

C#

if(GridView1.Rows.Count > 0){}

to wrap these statements in.

Hope it helps.

Azee...