Question

I get an error when I do the following:

if(Session['value'] != null) {    // code } 

The error i get is this:

Object reference not set to an instance of an object.

Why is this? I always check my session this way? I am using the MVC Framework, does this has something to do with it?

EDIT:

The code is in the constructor of a Controller:

public class MyController : ControllerBase {     private int mVar;      public MyController()     {         if (Session['value'] != null)         {             mVar= (int)Session['value'];         }     } } 

Answer 1

The session only really exists during the processing of an action – I wouldn’t expect it to be valid in the constructor of a controller. For example, the controller might (for all I know) be re-used between requests.

You will need to do this either in the action (method), or (perhaps more appropriately) in an action filter, or the OnActionExecuting (etc) method(s):

public abstract class ControllerBase : Controller {     protected override void OnActionExecuting(         ActionExecutingContext filterContext)     {         // code involving this.Session // edited to simplify         base.OnActionExecuting(filterContext); // re-added in edit     } }