How to Resolve - "Object reference not set to an instance of an object" Error in C#

Question

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Configuration;
using System.Data;

public partial class FormCreationWithDataStoraget : System.Web.UI.Page
{

    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void sbmt_Click(object sender, EventArgs e)
    {
        string connectionString = ConfigurationManager.ConnectionStrings["Data Source=RAJIM  -PC;Initial Catalog=RajiDatabase;Integrated Security=True"].ConnectionString;
        string insertSql = "INSERT INTO FamilyDetails(FirstName,LastName,Gender,Age,Relationship,MobileNumber)" + "values(@FirstName,@LaseName,@Gender,,@Age,@,@MobileNumber)";
        SqlConnection conn = new SqlConnection(connectionString);
        SqlCommand scmd = new SqlCommand();
        scmd.Connection = conn;
        scmd.CommandType = CommandType.Text;
        scmd.CommandText = insertSql;

        SqlParameter firstname = new SqlParameter("@FirstName", SqlDbType.VarChar, 40);
        firstname.Value = tbx.Text.ToString();
        scmd.Parameters.Add(firstname);

        SqlParameter lastname = new SqlParameter("@LaseName", SqlDbType.VarChar, 40);
        lastname.Value = tbx1.Text.ToString();
        scmd.Parameters.Add(lastname);

        SqlParameter gender=new SqlParameter("@Gender",SqlDbType.VarChar,40);
        gender.Value = rbt.SelectedItem.ToString();
        scmd.Parameters.Add(gender);

        SqlParameter age = new SqlParameter("@Age", SqlDbType.Int);
        age.Value = tbx2.Text.ToString();
        scmd.Parameters.Add(age);

        SqlParameter relationship = new SqlParameter("@Relationship", SqlDbType.VarChar, 40);
        relationship.Value = tbx3.Text.ToString();
        scmd.Parameters.Add(relationship);

        SqlParameter mobilenumber=new SqlParameter("@MobileNumber",SqlDbType.VarChar, 10);
        mobilenumber.Value = tbx4.Text.ToString();
        scmd.Parameters.Add(mobilenumber);


        try
        {
            conn.Open();
           scmd.ExecuteNonQuery();
           Response.Write("User Registration successful");
        }
        catch (SqlException ex)
        {
            string errorMessage = "Error in registering user";
            errorMessage += ex.Message;
            throw new Exception(errorMessage);

        }
        finally
        {
            conn.Close();
        }
    }

}

Answer 1

It looks like this line is causing your problem:

string insertSql = "INSERT INTO FamilyDetails(FirstName,LastName,Gender,Age,Relationship,MobileNumber)" + "values(@FirstName,@LaseName,@Gender,,@Age,@,@MobileNumber)";

Specifically:

@FirstName,@LaseName,@Gender,,@Age,@,@MobileNumber

It Should Be:

@FirstName,@LaseName,@Gender,@Age,@Relationship,@MobileNumber

Answer 2

The issue is that this line:

string connectionString = ConfigurationManager.ConnectionStrings["Data Source=RAJIM  -PC;Initial Catalog=RajiDatabase;Integrated Security=True"].ConnectionString;

is not retrieving any object because you don't have a ConnectionString defined your web.config with the name of "Data Source=RAJIM ..." so basically calling the .ConnectionString at the end of it breaks it.

Add the "Data Source=RAJIM..." line as a connection string in your web.config (more info on connection strings here).

Once you give your connection string a name, i.e., "MyConnectionString" then change your code to be:

string connectionString = ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString;