how to remove NullExceptionError from Session Variable - sql

Question

I have a varible sem,which takes inputfrom the textbox but if the textbox is kept empty i want it to return "Please Enter a Semester"
int sem;
int parsevalue;
if (int.TryParse(TextBox2.Text, out parsevalue))
{
sem = parsevalue;
Session["Sem"] = sem;
}
else
{
Literal2.Text = "Please Enter a Semester";
}
But If the Textbox is empty the Session["Sem"] returns NullExceptionError in the .aspx file where i have used it.
I searched for the proper conversion using tryparse but could not understand it clearly as to how to print the above mentioned error message.
please help
Thank you in advance

Answer 1

The problem here is that you're assigning the Session variable only when there is a correct value, but you're always trying to access it. This will fail if the value is incorrect (and the Session variable is not set).
Here's your corrected code:
int sem;
int parsevalue;
if (int.TryParse(TextBox2.Text, out parsevalue))
{
sem = parsevalue;
}
else
{
Literal2.Text = "Please Enter a Semester";
}
//Always set the Session variable when it's used somewhere else
Session["Sem"] = sem;

Answer 2

Try:
HttpContext.Current.Session["Sem"] = sem;
Actually:
Session.Add("Sem", sem);
and
Session["Sem"] = sem;
is a same

Answer 3

Q1 Hi , I have a varible sem,which takes inputfrom the textbox but if the textbox is kept empty i want it to return "Please Enter a Semester"
int sem;
int parsevalue;
var txt = TextBox2.Text
if (!String.IsNullOrEmpty(text) && int.TryParse(text, out parsevalue))
{
sem = parsevalue;
}
else
{
Literal2.Text = "Please Enter a Semester";
}
Session["Sem"] = sem;