What should I do if the current ASP NET session is null

Question

In my web application  I do something like this to read the session variables   if  HttpContext Current Session    null  amp  amp   HttpContext Current Session  MyVariable      null        string myVariable   string HttpContext Current Session  MyVariable        I understand why it s important to check why HttpContext Current Session  MyVariable   is null  the variable might not have been stored in the Session yet or the Session has been reset for various reasons   but why do I need to check if HttpContext Current Session is null   My understanding is that the session is created automatically by ASP NET therefore HttpContext Current Session should never be null  Is this assumption correct  If it can be null  does it mean I should also check it before storing something in it   if  HttpContext Current Session    null        HttpContext Current Session  MyVariable    Test     else          What should be done in this case  if session is null          Is it possible to force the session to be created if it doesn t exist

User · Answer

The following statement is not entirely accurate:

"So if you are calling other functionality, including static classes, from your page, you should be fine"

I am calling a static method that references the session through HttpContext.Current.Session and it is null. However, I am calling the method via a webservice method through ajax using jQuery.

As I found out here you can fix the problem with a simple attribute on the method, or use the web service session object:

There’s a trick though, in order to access the session state within a web method, you must enable the session state management like so:

[WebMethod(EnableSession = true)]

By specifying the EnableSession value, you will now have a managed session to play with. If you don’t specify this value, you will get a null Session object, and more than likely run into null reference exceptions whilst trying to access the session object.

Thanks to Matthew Cosier for the solution.

Just thought I'd add my two cents.

Ed

User · Answer

ASP NET Technical Articles     SUMMARY  In ASP NET  every Web page   derives from the System Web UI Page   class  The Page class aggregates an   instance of the HttpSession object for   session data  The Page class exposes   different events and methods for   customization  In particular  the   OnInit method is used to set the   initialize state of the Page object    If the request does not have the   Session cookie  a new Session cookie   will be issued to the requester    EDIT   Session  A Concept for Beginners     SUMMARY  Session is created when user   sends a first request to the server   for any page in the web application    the application creates the Session   and sends the Session ID back to the   user with the response and is stored   in the client machine as a small   cookie  So ideally the  machine that   has disabled the cookies  session   information will not be stored

User · Answer

Yes  the Session object might be null  but only in certain circumstances  which you will only rarely run into   If you have disabled the SessionState http module  disabling sessions altogether If your code runs before the HttpApplication AcquireRequestState event  Your code runs in an IHttpHandler  that does not specify either the IRequiresSessionState or IReadOnlySessionState interface   If you only have code in pages  you won t run into this  Most of my ASP  NET code uses Session without checking for null repeatedly  It is  however  something to think about if you are developing an IHttpModule or otherwise is down in the grittier details of ASP  NET  Edit In answer to the comment  Whether or not session state is available depends on whether the AcquireRequestState event has run for the request  This is where the session state module does it s work by reading the session cookie and finding the appropiate set of session variables for you  AcquireRequestState runs before control is handed to your Page  So if you are calling other functionality  including static classes  from your page  you should be fine  If you have some classes doing initialization logic during startup  for example on the Application Start event or by using a static constructor  Session state might not be available  It all boils down to whether there is a current request and AcquireRequestState has been run  Also  should the client have disabled cookies  the Session object will still be available - but on the next request  the user will return with a new empty Session  This is because the client is given a Session statebag if he does not have one already  If the client does not transport the session cookie  we have no way of identifying the client as the same  so he will be handed a new session again and again

User · Answer

In my case ASP NET State Service was stopped  Changing the Startup type to Automatic and starting the service manually for the first time solved the issue

User · Answer

If your Session instance is null and your in an  ashx  file  just implement the  IRequiresSessionState  interface   This interface doesn t have any members so you just need to add the interface name after the class declaration  C     public class MyAshxClass   IHttpHandler  IRequiresSessionState

[asp.net] What should I do if the current ASP.NET session is null?

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