Issue with global.asax - giving ArrayList to all new sessions in ASP.NET

Question

I want to expose an ArrayList defined in Global.asax to all sessions. Here is some code from Global.asax and Default.aspx:

public class Global : System.Web.HttpApplication
{

    public ArrayList userNameList = new ArrayList();
    protected void Application_Start(object sender, EventArgs e)
    {

    }

    protected void Session_Start(object sender, EventArgs e)
    {

    }
}


public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        Global global = new Global();
        User user = new User();
        user.username = TextBox1.Text;
        global.userNameList.Add(user);
        if (global.userNameList.Count != 0)
        {
            foreach (User u in global.userNameList)
            {
                ListBox1.Items.Add(String.Format(u.username));
            }
        }
    }
}

Please, tell me what I'm doing wrong. Thanks :)

Answer 1

The first thing you're doing wrong is trying to instantiate the Global class in a page. That is not going to work as you expect.

If you want to share an ArrayList (or anything else) amongst all sessions, you should probably use Application state instead: -

http://msdn.microsoft.com/en-us/library/ms178594(v=vs.100).aspx

You should also read up on synchronizing access to shared state as there may be potential threading issues, depending on what you're doing.

Answer 2

Remove anything you use in the global.asax file and use this code in your aspx page

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        User user = new User();
        user.username = TextBox1.Text;


        if (Cache["userList"] == null)
            Cache["userList"] = new ArrayList();

        ((ArrayList)Cache["userList"]).Add(user);

        foreach (User u in (ArrayList)Cache["userList"])
        {
            ListBox1.Items.Add(String.Format(u.username));
        }
    }
}

Make sure to refactor your code because you will easily run into maintenance issues, plus it's not unit testable at all. Hope it helps

Leo