how to use session properly?

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HI. Can somebody help me? I'm trying to put a field(data) from my database to a label in my web app. and I get an error in the session part(the bolded and underlined one) saying "Object reference not set to an instance of an object." I don't know what to do. here is my code:

C#

string ConnString = "Server=SAMSUNG-PC;Database=ISPROG3MP;INTEGRATED SECURITY=SSPI";
        SqlConnection scnMP;
scnMP = new SqlConnection(ConnString);

            if (!this.IsPostBack)
            {
                scnMP.Open();

                //get userid from session
                ID = Session["StudentID"].ToString();


                //get the username from DB
                string getUserName = "SELECT FirstName FROM Students ";
                getUserName += "WHERE StudentID = " + ID;

                SqlCommand scmUsers = new SqlCommand(getUserName, scnMP);
                SqlDataReader sdrUsers = scmUsers.ExecuteReader();
                sdrUsers.Read();

                string strUserName = sdrUsers["UserName"].ToString();

                //load username in label: welcome <username>
                lblName.Text = strUserName;
                sdrUsers.Close();

                //select user profile
                string strProfile = "SELECT FirstName, LastName, School, Course ";
                strProfile += " FROM Students ";
                strProfile += " WHERE StudentID = " + ID;

                SqlCommand scmProfile = new SqlCommand(strProfile, scnMP);
                SqlDataReader sdrProfile = scmProfile.ExecuteReader();


                if (sdrProfile.HasRows)
                {
                    sdrProfile.Read();
                    //load user profile
                    lblFN.Text = sdrProfile["FirstName"].ToString();
                    lblLN.Text = sdrProfile["LastName"].ToString();
                    lblS.Text = sdrProfile["School"].ToString();
                    lblC.Text = sdrProfile["Course"].ToString();
                }

                scnMP.Close();
            }

I'm trying to put like.. when the page load,
There states that..

"WELCOME [here appears the name of the user]"
Please Help. Thanks!

Posted 8-Jul-13 5:42am

sensitive tomato

Updated 8-Jul-13 6:36am

Maciej Los

v2

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[no name] 8-Jul-13 11:48am

You would have to set Session["StudentID"] to be some value before it would be not null.

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Rajan Maheshwari · Accepted Answer · 2013-07-08T06:31:00

Its because you have not set the session variable.
Just do one thing.make a login page with username in textbox1
Create a Session variable then
Then Session["username"]=textbox1.text;
Then on click of login when you redirect to other page in that page_load event put

C#

page_load()
{
if(Session["username"]!=null)
{
//Your 2nd page code here whatever you want to write
}

else
{
Response.Redirect("Login.aspx");
}
}

Hope it helps...