Getting Error: Object reference not set to an instance of an object.

[Muralikrishna]

HI,
I was created consultant registration page using ASP.NET 4.0, and also created database, my database name is "registration.mdf", i just wrote this below code, when debugging my page getting one error like "Object reference not set to an instance of an object". Attached the document also(screen shots)!



Web.config code:

 <connectionStrings>
 
        <add name="ApplicationServices" connectionString="data source=.TEKPC26\\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=registration.mdf;User Instance=true" providerName="System.Data.SqlClient"/>
    </connectionStrings>
 

BUTTON CLICK CODE:

 protected void Button1_Click(object sender, EventArgs e)
    {
 
        SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["registration"].ToString());
        con.Open();
        cmd=new SqlCommand("insert into values('" + TextBox1.Text + "','" + TextBox2.Text + "','" + TextBox3.Text+"')",con);
        cmd.ExecuteNonQuery();
 
    }
 

[Frinavale]

You named your connection string "ApplicationServices" in your web.config file.

You need to use this name in your C# code that you are using to retrieve the connection string....currently you are not doing so.

-Frinny

[Maraj]

You need to write your connection string name in the sql connection object like this

 SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["ApplicationServices"].ToString());

Also always try to write your code in try-catch block this will give you clear picture of exception.

try
{
//Your code
}
catch(exception ex)
 
{
//Display exception
}

[Muralikrishna]

"Error: Object reference not set to an instance of an object.(NullReferenceException was unhandled by user code)"

Can you please suggest me to come out of the error !.

I was created registration page, and also created database. when we submit that registration fields that fields should be stored in database(my database name is "registration"). i think it's connection strings problem.I written a code in "Web.config" for connection string.



Can you please suggest me to come out of the error !.


CODE:

using System;
using System.Configuration;
using System.Data;
using System.Collections.Generic;
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 Default2 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
 
    }
    SqlConnection con = new SqlConnection("Data Source=TEKPC26\\SQLEXPRESS;Initial Catalog=registration;Integrated Security=True");
    SqlCommand cmd;
    protected void Button1_Click(object sender, EventArgs e)
    {
 
        SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["registration"].ToString());
        con.Open();
        cmd=new SqlCommand("insert into values('" + TextBox1.Text + "','" + TextBox2.Text + "','" + TextBox3.Text+"')",con);
        cmd.ExecuteNonQuery();
 
    }
}

AND

Web.config CODE:

<configuration>
 
  <connectionStrings>
 
        <add name="ApplicationServices" connectionString="data source=.TEKPC26\\SQLEXPRESS;
         Integrated Security=SSPI;AttachDBFilename=C:\\Documents and Settings\\Administrator\\My Documents\\Visual Studio 2010\\WebSites\\WebSite1\\App_Data\\registration.mdf;
         User Instance=true&quot; providerName=&quot;System.Data.SqlClient" />
    </connectionStrings>

[Frinavale]

I guess you didn't understand my original answer.
In your web.conf file you have specified a "name" attribute for your connection string. You need to use this name as the "key" for ConfigurationManager order to retrieve the connection string from the web.config file.

Based on the code that you originally posted you would have to change 1 thing in your button click event...you need to provide "ApplicationServices" as the key to the ConfigurationManager instead of "registration". (Even though "registration" may be the name of the database that you are connecting to, you named the connection string in your web.config "ApplicationServices")

This is your original web.config code:

 <connectionStrings>
 
  <add name="ApplicationServices" connectionString="data source=.TEKPC26\\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=registration.mdf;User Instance=true" providerName="System.Data.SqlClient"/>
    </connectionStrings>
 

This is the modified button click event based on the original code you posted:

protected void Button1_Click(object sender, EventArgs e)
    {
 
        SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["ApplicationServices"].ToString());
        con.Open();
        cmd=new SqlCommand("insert into values('" + TextBox1.Text + "','" + TextBox2.Text + "','" + TextBox3.Text+"')",con);
        cmd.ExecuteNonQuery();
 
    }
 

Now, if you want to be clear about which database the connection string connects to it might be a better idea to change the "name" of your connection string in your web.config file and leave your button click the same...

Like this:

This is the modified web.config code based on your original web.config code:

 <connectionStrings>
 
  <add name="registration" connectionString="data source=.TEKPC26\\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=registration.mdf;User Instance=true" providerName="System.Data.SqlClient"/>
    </connectionStrings>
 

This is the original button click event code you posted:

protected void Button1_Click(object sender, EventArgs e)
    {
 
        SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["registration"].ToString());
        con.Open();
        cmd=new SqlCommand("insert into values('" + TextBox1.Text + "','" + TextBox2.Text + "','" + TextBox3.Text+"')",con);
        cmd.ExecuteNonQuery();
 
    }
 

So either you need to change the name of your connection string as defined in your web.config file or you need to change the name provided to the ConfigurationManager. Either approach works.

-Frinny

[Muralikrishna]

I just replaced your code, when executing the program getting one error! like..

ERROR:sqlexception was unhandled by user code.

"A network related or instance-specific error occurred while establishing a connection to sql server.the server was not found or was not accessible. Verify that the instance name is correct and that sql server is configured to allow remote connections."