Scope of static inner class in ASP.NET

Question

I am unsure about the scope of one static inner class of a non-static class.

In the lines below, would the variable DataContextCreator.Instance (part of a Singleton pattern) point to the same PDataContext instance for all Page objects/page requests or would each object have its own instance?

public class Page : System.Web.UI.Page
{

    private class DataContextCreator
    {
        static DataContextCreator() { }

        public static readonly PDataContext Instance = new PDataContext(TUtil.GetConnectionString());
    }

    public PDataContext DataContext
    {
        get
        {
            return DataContextCreator.Instance;
        }
    }
}

Do I have to work with HttpContext.Current for this to work in the desired way, ie no shared DataContext? If so, is there another way?

I am not sure whether modifying the static class to private (as I have done) does the trick.

Thanks!

EDIT: This is my solution where I now have the same lazy-loading capability but without static variables. I don't think I need to put a mutex lock around the holding variable in this case.

    private PDataContext _DataContext;
    private PDataContext DataContext
    {
        get
        {
            if (this._DataContext == null)
            {
                this._DataContext = new PDataContext(TUtil.GetConnectionString());
            }
            return this._DataContext;
        }
    }

Answer 1

It would be the same for every page. A static variable is a static variable, however nested it is. (Generics make things "interesting" in that a static variable in Foo<int> is separate to the one in Foo<string> etc, but that's not relevant here.)

If you want to make something depend on the instance of the Page , it needs to be an instance variable within Page . (I'd advise against naming a case the same as its base class, by the way.)

Answer 2

Nested classes are purely for naming convenience (and some modifier changes (private etc)). They are actually the same as regular (top-level) classes in terms of behaviour. So Instance is shared completely (it is not tied to an Page instance).

Answer 3

As the Instance variable is static, it only exists once, so all threads share the same value. Putting the variable in another class doesn't change how a static variable works.

To make a singleton that is local to the page instance, you would store the reference in the page context:

public PDataContext DataContext {
   get {
      PDataContext result = HttpContext.Current["PData"];
      if (result == null) {
         result = new PDataContext(TUtil.GetConnectionString());
         HttpContext.Current["PData"] = result;
      }
      return result;
   }
}