Singleton-Pattern ASP.NET C# for each user

Question

Hi all, i'm building a web application with asp.net c# and i have a class that i want to use in multiple pages witouth instantiate it every time. I need to load the data in it and never lose them during the user session time. I thought about the singleton-pattern but it shared the instance of the class beetween browsers. How can i solve the problem?

Answer 1

Singleton is not the answer. Look at Session State, ViewState and Cookies.

Answer 2

UserData data = new UserData(somedata);

Session["UserData"] = data;

next page

UserData data = (UserData) Session["UserData"];

Answer 3

If you have inproc session state you can use something like this

class Singleton
{
    static object locker = new Object();

    public static Singleton Instance
    {
        get
        {
            var inst = HttpContext.Current.Session["InstanceKey"] as Singleton;
            if (inst == null)
            {
                lock (locker)
                {
                    inst = HttpContext.Current.Session["InstanceKey"] as Singleton;
                    if (inst == null)
                    {
                        inst = new Singleton();
                        HttpContext.Current.Session["InstanceKey"] = inst;
                    }
                }
            }
            return inst;
        }
    }
}

Code can be improved, to avoid locking for all users. Don't know if this is a good idea to implement Singleton like that, I'd recommend you to see if you can design your code in other way.

Answer 4

public sealed class MyClass
    {
        private static object sync = new object();

        private MyClass()
        {
            test = new Random().Next(1, 5).ToString();
        }

        public string test;

        public static MyClass Instance()
        {
            if (!HttpContext.Current.Items.Contains("mykey"))
            {
                lock (sync)
                {
                    if (HttpContext.Current.Items["mykey"] == null)
                    {
                        HttpContext.Current.Items.Add("mykey", new MyClass());
                    }
                }
            }

            return (MyClass)HttpContext.Current.Items["mykey"];
        }
    }

this is my actually my sample test class. i load the page for the first time and i create the instance of the class. I reload the page and i have a new class instance. With debugger i can see that the Items collection is resetted... Why?