"NullReferenceException code Unhandled by user code"

[Priti Sharma]

string cat = Request.QueryString[

When I am using this code gives an error message as

"NullReferenceE xception code Unhandlled by user code"

Please reply.........

[Rabbit]

At the very least we would need to see the rest of the code on that line.

[Priti Sharma]

This is my entire code for update category please check this!!!!


The error is NullReferenceEx ception unhandlled by user code.

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;
using System.Data.SqlClient;

public partial class update : System.Web.UI.Page
{
    private SqlConnection scon;
    private SqlCommand cmd;
    private SqlDataReader dr;
    int cid;
    string select;
    string u;
    protected void Page_Load(object sender, EventArgs e)
    {
        scon = new SqlConnection("Data Source=.\\Sqlexpress;initial catalog =BDB;integrated security =true");
        scon.Open();
        string cat = Request.QueryString["catid"].ToString();
        cid = Convert.ToInt32(cat);
        if (cid == 1 | cid == 2 | cid == 3)
        {

            select = "select * from computer_education where category_id=" + cid;
        }
        if (cid == 4 | cid == 5 | cid == 6)
        {

            select = "select * from children_books where category_id=" + cid;

        }
        if (cid == 7 | cid == 8)
        {

            select = "select * from cooking where category_id=" + cid;
        }
        if (cid == 11 | cid == 12 | cid == 13)
        {

            select = "select * from religion where category_id=" + cid;

        }

        if (cid == 18 | cid == 19 | cid == 20)
        {

            select = "select * from Entertainment where category_id=" + cid;

        }
        if (cid == 21 | cid == 22)
        {

            select = "select * from science where category_id=" + cid;

        }
        if (cid == 23 | cid == 24)
        {

            select = "select * from Business_investing where category_id=" + cid;

        }
        cmd = new SqlCommand(select, scon);

        dr = cmd.ExecuteReader();
        while (dr.Read())
        {
            ListItem newitem = new ListItem();
            newitem.Text = dr["book_name"].ToString();
            newitem.Value = dr["item_id"].ToString();
            DropDownList2.Items.Add(newitem);
        }
        dr.Close();
  

    }

    protected void Button1_Click(object sender, EventArgs e)
    {
     try
        {
            if (cid == 1 | cid == 2 | cid == 3)
            {

                u = "update computer_education set price=@price where item_id=@item_id";
            }
            if (cid == 4 | cid == 5 | cid == 6)
            {

                u = "update children_books set price=@price where item_id=@item_id";

            }
            if (cid == 7 | cid == 8 )
            {

                u = "update cooking set price=@price where item_id=@item_id";
            }
            if (cid == 11 | cid == 12 | cid == 13)
            {

                u = "update religion set price=@price where item_id=@item_id";

            }
            
            if (cid == 18 | cid == 19 | cid == 20)
            {

                u = "update Entertainment set price=@price where item_id=@item_id";

            }
            if (cid == 21 | cid == 22)
            {

                u = "update science set price=@price where item_id=@item_id";

            }
            if (cid == 23 | cid == 24)
            {

                u = "update Business_investing set price=@price where item_id=@item_id";

            }
            cmd = new SqlCommand(u, scon);
            cmd.Parameters.AddWithValue("@price", Decimal.Parse(TextBox6.Text));
            cmd.Parameters.AddWithValue("@item_id", DropDownList2.SelectedItem.Value);
            cmd.ExecuteNonQuery();
            Label24.Visible = true;
            Label24.Text = "Price Updated Successfully";
        }

        catch (Exception err)
        {
            Label24.Visible = true;
            Label24.Text = "Not updated" + err.Message.ToString();
        }
    

     }
}

[Rabbit]

Your query string probably doesn't have catid defined. Either because it's not being passed or because it is named something else. Check the form that is passing the value.