public static void AddObserver(Observer o)
    {
        if(!observers.Contains(o))
            observers.Add(o);

        System.Diagnostics.Debug.WriteLine("Observer tilføjet : " + observers.Count);
    }

    public static void RemoveObserver(Observer o)
    {
        if (observers.Contains(o))
            observers.Remove(o);

        System.Diagnostics.Debug.WriteLine("Observer fjernet : " + observers.Count);
    }

    public static void NotifyObserversNewMail(Observer observer)
    {
        foreach (Observer o in observers)
            if(!o.Equals(observer))
                o.UpdateNewMail();
    }

public partial class SiteMaster : System.Web.UI.MasterPage, Observer
{
    protected void Page_Unload(object sender, EventArgs e)
    {
        Session["observer"] = this;
        Global.AddObserver(this);
    }

    protected void Page_Load(object sender, EventArgs e)
    {
        //ADD OBSERVER TO GLOBAL.ASAX
        if (Session["observer"] != null)
            Global.RemoveObserver((Observer)Session["observer"]);

    public void Update()
    {
        DLMessages.DataSource = ServiceMessages.GetInstance().GetMessages();
        DLMessages.DataBind();

        UPMessages.Update();
    }

protected void MessageSend(object source, EventArgs args)
    {
        Page.Validate("ValGroupMessageTo");
        if (Page.IsValid)
        {
              ServiceMessages.GetInstance().SendMessage(ServiceCommunity.GetInstance().GetUser(MessageTo.Text).Id, ((User)Session["user"]).Id, MessageMessage.Text);

            Global.NotifyObserversNewMail((Observer)Session["observer"]);

            ClosePopups(new object(), new EventArgs());

            Update();
        }
    }