Object reference not set to an instance of an object.

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i run the code and following error occur

Object reference not set to an instance of an object.

i have a master page and place label and button in which when user login the show his name and logout button

in master page page load code is

<pre lang="c#">public partial class Site1 : System.Web.UI.MasterPage
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (Context.User.Identity.IsAuthenticated)
            {

                WELCOME.Text = Session["Login2"].ToString();
                WELCOME.Text = Session["Login4"].ToString();

            }
            else
            {

                Session["Login2"] = null;
            }

        }

        protected void LGOT_Click(object sender, EventArgs e)
        {
            Session.Abandon();
            Session.Clear();
            Response.Redirect("Login.aspx");


        }
    }

Posted 6-Apr-13 5:22am

ariesareej

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OriginalGriff · Accepted Answer · 2013-04-06T05:44:00

Solution 1

Two things spring to mind:
1) You are setting the same string to two different values in successive lines of code:

C#

WELCOME.Text = Session["Login2"].ToString();
WELCOME.Text = Session["Login4"].ToString();

The first will have no affect on the string as it's value will be overwritten.

2) The same two lines are the ones causing your problem.
If the value "Login2" (or "Login4") is not found in the session variables, then the returned value will be null - at which point the attempt to call the ToString method will fail with an "Object reference not set to an instance of an object." error.
Check them before you use them:

C#

object login2 = Session["Login2"];
object login4 = Session["login4"];
if (Context.User.Identity.IsAuthenticated && login2 != null && login4 != null)
   {
   WELCOME.Text = login4.ToString();
   }

Posted 6-Apr-13 5:44am

OriginalGriff

Comments

vinodkumarnie 6-Apr-13 13:51pm

Well said sir...

ariesareej 7-Apr-13 4:20am

for login2 we create another or i write in this
object login2 = Session["Login2"];
object login4 = Session["login4"];
if (Context.User.Identity.IsAuthenticated && login2 != null && login4 != null)
{
WELCOME.Text = login4.ToString();
WELCOME.Text = login2.ToString();
}

OriginalGriff 7-Apr-13 4:37am

As I said: the second line will be used, the first will have no effect (unless you have created your own class with a Text property and are doing something very, very nasty with it - if so, don't do that via a property, use a method instead so it is obvious you are adding data rather than overwriting it).
It's just like saying:
int i;
i = 6;
i = 8;
The value of "i" after this code will always be "8", the lines setting "6" will always be ignored.

If you want to put both values into the Text property, then you need to add them in:
string str;
str = "hello";
str = str + "world";
Or
string str;
str = "hello";
str += "world";
Or in your case:
WELCOME.Text = string.Format("{0} {1}", login4, login2);
to separate the two items.