can't use Session in a class that is using inherited in asp.net

I've created a webpage which is inherited from another class something like :

class webpage : startup {
.
.
.
}


class startup :  System.Web.UI.Page  {

}

and inside startup class I'm trying to use

Session["blah"] = "some other blah";

but whenever I run this code I'll get the following error :

Session state can only be used when enableSessionState is set to true, either in a configuration file or in the Page directive. Please also make sure that System.Web.SessionStateModule or a custom session state module is included in the \\ section in the application configuration.

I'll get error even after changing web.config to accept Session but again the same result ------------------------edit--------------------

I know I can use Httpcontext.current.session but this approad also give me error saying : "you can't use null instance or something like开发者_如何学Python that" what should I do?

I've created a BasePage class as follows:

namespace JWC.Examples.WebForms.Base {
   public class BasePage: Page {
   }
}

And a default page that inherits from BasePage:

namespace JWC.Examples.WebForms {
   public partial class _Default : BasePage {
      protected void Page_Load(object sender, EventArgs e) {
         if (Session["SomeItem"] == null)
            Session["SomeItem"] = 42;
      }
   }
}

I have no problems accessing session at all. Not sure what the issue is, but having inherited from another class beside Page is most likely a red herring.

This one is going to be difficult to diagnose without including a lot of details. The best advice I can give is to create a blank ASP.Net project, and start porting things over one by one so you can eliminate possibilities systematically.

UPDATE

Mr. Powers was kind enough to send me a test solution that recreated the problem.

The issue lies within the idiosyncrasies of the ASP.Net Page Life Cycle. The offending code looked something like this:

public class BasePage: Page
{
    public BasePage()
    {
        //Do some stuff with Session
    }
}

Unfortunately, trying to access Session in the constructor is a non-starter because the Request and Response objects aren't set until after the constructor is called. The trick is to move your code into a stage where those things have been initialized, but before other dependent code might need to take advantage of it.

The PreInit event will do the trick. If you get rid of the constructor, and override the OnPreInit event, then everything should be fine. Like this:

protected override void OnPreInit(EventArgs e)
{
    base.OnPreInit(e);

    //Do some stuff with Session
}

Understanding the Page lifecycle is a critical component to doing anything in ASP.Net. One should read the MSDN documentation thoroughly before proceeding any further with Web Forms as it will save many a headache down the road.

try this

class webpage : startup {
   …
}

class startup :  System.Web.UI.Page  {
    protected override void OnPreInit(EventArgs e)
    {
        base.OnPreInit(e);
        var session = HttpContext.Current.Session["...."];
    }
}

So the session is not in the constructor of the Startup, but in the override of OnPreInit instead.