about session destroy

Let's assume you have a site with a master page that has a few simple pages and that the user has logged in. As part of the login process assign something to the Session, perhaps like

Session.Add(Key, Value);

. You can then test for this value each time the user, for instance, navigates to another page or initiates a PostBack event.

You could do:

// Pseudo code.
if (Session[Key] == null)
{
    // Do something: user no longer valid.
}

If the Session has expired the Session variable will be null which you can test for and take the appropriate action.