ASP.NET session is NULL despite a IRequireSessionState/IReadOnlySessionState handler?

Question

While looking into another problem I met a peculiar situation.

Within the Global.asax method I have the following code:

protected void Application_AcquireRequestState(object sender, EventArgs e)
{
    if (!(Context.Handler is IRequiresSessionState || Context.Handler is IReadOnlySessionState)) // No session - no validation.
        return;
    DoSomething();
}

The DoSomething() method call throws a NullReferenceException and it is simple enough that the only place it could do that was if HttpContext.Current.Session was null.

How can this be?

Answer 1

At that time HttpContext.Current.Session may well be null. The event is firing at the point where the session is being aquired there is no guarantee that at this point it has been aquired. One reason you might hook this event is because you are providing a custom module to implement your own Session object. It would be here that such a custom module would set the Session.

If you want to use the Session object you should be using the PostAquireRequestState event.