asp.net set sessions before postback - asp.net

Question

is there an easy way, to store all needed global variables in sessions at once, before the PostBack starts? Or have I to store them in each step where I change them?
I will do something like:
// Global variable.
bool test = true;
// Store all needed information in a session.
protected void Before_globalvariable_is_set_to_default_value(...)
{
Session["Test"] = test;
...
}
protected void Page_Load(object sender, EventArgs e)
{
if(IsPostBack)
{
//if(Session["Test"] != null)
//{
test = (bool)Session["Test"];
Session.Contents.Remove("Test");
//}
}
}
Is something like that possible?
Additional Information
At the Page_Load (!IsPostBack) I check if the user gets more vision, if he gets, I set a global var to true. Later in my code I check if that var is true and add additional columns to a GridView.
Now if a PostBack occurs, I can’t check that var, because I lose the information. I knew that I need to store the information in a Session. If I set the Session at the time where I set the global var to true, I get problems with the session timeout (If the user is on the site, but doesn’t do something for a while). So I thought it will be good, if I set the Session shortly before I lose the information of the global var and delete the Session after reinitialization.
That’s my idea, but I don’t know if something like that is possible.
Edit2:
If I do following it works:
//Global variable
bool test = false;
protected void Page_PreRender(object sender, EventArgs e)
{
Session["Test"] = test;
}
protected void Page_Load(object sender, EventArgs e)
{
if (IsPostBack)
{
test = (bool)Session["Test"]; // Session is true!!!
Session.Contents.Remove("Test");
}
else
{
test = true; // Set at the PageLoad the var to true.
}
}
I’m a little bit confused, I thought PreRender is after the PageLoad, why suddenly the test var is true and if I remove the PreRender it isn’t?
Greetz

Answer 1

If you're worried about losing a specific value between requests, because you've maintained the state of that variable in the Session object and it might have been cleared by a timeout, you could consider using another, more durable, mechanism to save the state: for example, cookies or database.

Answer 2

If the value only needs to live during that one Request, you can use class-level fields of the code-behind class. Set them in the Init or Load phase, then you can use those values in all other phases.
For a lifetime of just a single request:
public partial class MyPage: Page
{
private bool test = true;
public void Page_Load(...)
{
// maybe set 'test' to another value
}
public void Button_Click(...)
{
// you can still access 'test'
}
public void Page_PreRender(...)
{
// you can still access 'test'
}
}
If however you need that value to live from request to the next postback, you can use ViewState instead of Session. Advantage: no timeout as it is stored in the html and posted back from the browser along with other data. Disadvantage: it only works in postback-scanario's, not when you link to a different page.