[System.NullReferenceException: Object reference not set to an instance of an object.] - asp.net

Question

I am trying to select a user from my default_information.aspx.cs page and display that user information on my registration.aspx page where I already created a registration form.
I am getting System.NullReferenceException:Object reference not set to an instance of an object error. Please help me. I've given the main part of it. I debugged it. I found every data is selected from my DB in string strusername,strpassword. But code breaks on usernametxt.Text = strusername; when i try to show username or password on that text field.
default_information contains
protected void gridviewprofile_SelectedIndexChanged(object sender, EventArgs e)
{
registration objdef = new registration();
string username = gridviewprofile.Rows[gridviewprofile.SelectedIndex].Cells[1].Text;
objdef.displayuser(username);
}
protected void update_Click(object sender, EventArgs e)
{
Response.Redirect("registration.aspx");
}
registration.aspx contains
protected void register_Click(object sender, EventArgs e)
{
user objuser = new user();
objuser.username = usernametxt.Text;
objuser.password = passwordtxt.Text;
objuser.email = emailtxt.Text;
objuser.Save();
}
public void displayuser(string username)
{ user obj = new user();
DataSet objDataset = obj.profile(username);
string strusername = objDataset.Tables[0].Rows[0][0].ToString();
string strpassword = objDataset.Tables[0].Rows[0][1].ToString();
string stremail = objDataset.Tables[0].Rows[0][2].ToString();
usernametxt.Text = strusername;
passwordtxt.Text = strpassword;
emailtxt.Text = stremail;
}
user class contains
public class user
{
public void Save()
{
clssqlserver obj = new clssqlserver();
obj.insertuser_info(Username,Password,Email);
}
public DataSet profile(string username)
{
clssqlserver obj = new clssqlserver();
return obj.getalluser_info(username);
}
}
clssqlserver contains
public DataSet getalluser_info(string username)
{
string connectionstring = "Data Source=localhost\\mssql;Initial Catalog=blooddb;Integrated Security=True";
SqlConnection objconnection = new SqlConnection(connectionstring);
objconnection.Open();
string command = "Select * from login_donor where username='" + username + "' ";
SqlCommand objcommand = new SqlCommand(command, objconnection);
DataSet objdataset = new DataSet();
SqlDataAdapter objadapter = new SqlDataAdapter(objcommand);
objadapter.Fill(objdataset);
objconnection.Close();
return objdataset;
}
public bool insertuser_info(string username,string password,string email)
{ string connectionstring = "Data Source=localhost\\mssql;Initial Catalog=blooddb;Integrated Security=True";
SqlConnection objconnection = new SqlConnection(connectionstring);
objconnection.Open();
string strInsertCommand = "insert into login_donor values('"+ username +"','"+ password + "','"+email+"')";
SqlCommand objcommand = new SqlCommand(strInsertCommand, objconnection);
objcommand.ExecuteNonQuery();
objconnection.Close();
return true;
}

Answer 1

It looks like you are using the asp.net create user wizard control.Because your controls are buried inside another container, you have to be rewarded after some little excavation..Lets start digging......
Using the wizard which is already accessible locate your text box
TextBox usernametxt= (TextBox)CreateUserWizard.FindControl("usernametxt");
usernametxt.Text = strusername;
Hope this will help.

Answer 2

You should check this line
string strusername = objDataset.Tables[0].Rows[0][0].ToString();
you are trying to access directly objDataset.Tables[0], what if there is no user with the supplied username to this method getalluser_info(string username), will the dataset fill the table.
you should first check whether there is any table in the dataset or not.
hope this helps

Answer 3

well i ve found the solution...i was passing Data Between Webforms in worng way..here is the link which helps me: http://dotnetslackers.com/community/blogs/haissam/archive/2007/11/26/ways-to-pass-data-between-webforms.aspx
here is the solution
default_information.aspx contains
protected void gridviewprofile_SelectedIndexChanged(object sender, EventArgs e)
{ string username = gridviewprofile.Rows[gridviewprofile.SelectedIndex].Cells[1].Text;
Response.Redirect("registration.aspx?id="+username);
}
registration.aspx contains:
protected void Page_Load(object sender, EventArgs e)
{
string queryStringID = Request.QueryString["id"];
displayuser(queryStringID);
}
public void displayuser(string username)
{ user obj = new user();
DataSet objDataset = obj.profile(username);
string strusername = objDataset.Tables[0].Rows[0][0].ToString();
string strpassword = objDataset.Tables[0].Rows[0][1].ToString();
string stremail = objDataset.Tables[0].Rows[0][2].ToString();
usernametxt.Text = strusername;
passwordtxt.Text = strpassword;
emailtxt.Text = stremail;
}