GUI Windows Form C#

/*
Professional Windows GUI Programming Using C#
by Jay Glynn, Csaba Torok, Richard Conway, Wahid Choudhury, 
   Zach Greenvoss, Shripad Kulkarni, Neil Whitlow
Publisher: Peer Information
ISBN: 1861007663
*/
using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.Diagnostics;
using System.Runtime.CompilerServices;
namespace UserEvents
{
    /// 
    /// Summary description for Form1.
    /// 

    public class UserEvents : System.Windows.Forms.Form
    {
        private System.Windows.Forms.TextBox txtUsername;
        private System.Windows.Forms.Button btnLogin;
        /// 
        /// Required designer variable.
        /// 

        private System.ComponentModel.Container components = null;
        LoginAuditInserter la = new LoginAuditInserter();
        public UserEvents()
        {
            //
            // Required for Windows Form Designer support
            //
            InitializeComponent();
            //
            // TODO: Add any constructor code after InitializeComponent call
            //
            
            la.LoginAudit += new LoginAuditInserter.LoginAuditHandler(AddAuditEntry);
            la.LoginAudit += new LoginAuditInserter.LoginAuditHandler(AddEventLogEntry);
        }
        static public void AddAuditEntry(string username)
        {
            System.Diagnostics.Debug.WriteLine(username);
        }
        static public void AddEventLogEntry(string username)
        {
            string applicationName = "Login Audit";
            EventLog ev = new EventLog("Application");
            ev.Source = applicationName;
            ev.WriteEntry("Login Attempted.", EventLogEntryType.Information);
        }
        /// 
        /// Clean up any resources being used.
        /// 

        protected override void Dispose( bool disposing )
        {
            if( disposing )
            {
                if (components != null) 
                {
                    components.Dispose();
                }
            }
            la.LoginAudit -= new LoginAuditInserter.LoginAuditHandler(AddAuditEntry);
            la.LoginAudit -= new LoginAuditInserter.LoginAuditHandler(AddEventLogEntry);
            base.Dispose( disposing );
        }
        #region Windows Form Designer generated code
        /// 
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// 

        private void InitializeComponent()
        {
            this.txtUsername = new System.Windows.Forms.TextBox();
            this.btnLogin = new System.Windows.Forms.Button();
            this.SuspendLayout();
            // 
            // txtUsername
            // 
            this.txtUsername.Location = new System.Drawing.Point(8, 24);
            this.txtUsername.Name = "txtUsername";
            this.txtUsername.Size = new System.Drawing.Size(152, 20);
            this.txtUsername.TabIndex = 0;
            this.txtUsername.Text = "";
            // 
            // btnLogin
            // 
            this.btnLogin.Location = new System.Drawing.Point(184, 24);
            this.btnLogin.Name = "btnLogin";
            this.btnLogin.Size = new System.Drawing.Size(96, 23);
            this.btnLogin.TabIndex = 1;
            this.btnLogin.Text = "Login";
            this.btnLogin.Click += new System.EventHandler(this.btnLogin_Click);
            // 
            // UserEvents
            // 
            this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
            this.ClientSize = new System.Drawing.Size(292, 78);
            this.Controls.AddRange(new System.Windows.Forms.Control[] {
                                                                          this.btnLogin,
                                                                          this.txtUsername});
            this.MaximizeBox = false;
            this.Name = "UserEvents";
            this.Text = "Login";
            this.ResumeLayout(false);
        }
        #endregion
        /// 
        /// The main entry point for the application.
        /// 

        [STAThread]
        static void Main() 
        {
            Application.Run(new UserEvents());
        }
        private void btnLogin_Click(object sender, System.EventArgs e)
        {
            la.AddAuditEntry(txtUsername.Text);     
        }
    }
    public class LoginAuditInserter
    {
        public delegate void LoginAuditHandler(string username);
        private AccessorContainer container = new AccessorContainer();
        private static int key = 0;
        public event LoginAuditHandler LoginAudit
        {
            [MethodImpl(MethodImplOptions.Synchronized)]
            add
            {
                container.Add(key, value);
            }
            [MethodImpl(MethodImplOptions.Synchronized)]
            remove
            {
                container.Remove(key, value);
            }
        }
        protected void OnLoginAudit(string username)
        {
            LoginAuditHandler loginAudit = (LoginAuditHandler)container.Get(key);
            if(username!=null)
            {
                loginAudit(username);
            }
        }
        public void AddAuditEntry(string username)
        {
            OnLoginAudit(username);
        }
    }
    public class AccessorContainer
    {
        private ArrayList arrayAccessor = new ArrayList();
        public Delegate Get(int key)
        {
            return ((Delegate)arrayAccessor[key]);
        }
        public void Add(int key, Delegate ptr)
        {
            try
            {
                arrayAccessor[key] = Delegate.Combine((Delegate)arrayAccessor[key], ptr);
            }
            catch(ArgumentOutOfRangeException)
            {
                arrayAccessor.Add(ptr);
            }
        }
        public void Remove(int key, Delegate ptr)
        {
            arrayAccessor.Remove(Delegate.Remove((Delegate)arrayAccessor[key], ptr));
        }
    }
}