namespace Delegates
{
    partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            clock = new Clock(digital);
        }

        private void start_Click(object sender, System.EventArgs e)
        {
            this.clock.Start();
        }

        private void stop_Click(object sender, System.EventArgs e)
        {
            this.clock.Stop();
        }

        private Clock clock;
    }
}

namespace Delegates
{
    using System.Windows.Forms;

    class Clock
    {
        public Clock(TextBox displayBox)
        {
            this.display = displayBox;
        }

        public void Start()
        {
            pulsed.Add(this.RefreshTime);
        }

        public void Stop()
        {
            pulsed.Remove(this.RefreshTime);
        }

        private delegate void InvokeCallback(string msg);
        private void RefreshTime(int hh, int mm, int ss)
        {
            if (!this.display.InvokeRequired)
            {
                this.display.Text = string.Format("{0:D2}:{1:D2}:{2:D2}", hh, mm, ss);
            }
            else
            {
                InvokeCallback msgCallback = new InvokeCallback(DisplayText);
                display.Invoke(msgCallback, new object[] { string.Format("{0:D2}:{1:D2}:{2:D2}", hh, mm, ss) });

            }

        }

        private void DisplayText(string text)
        {
            this.display.Text = text;
        }

        private Ticker pulsed = new Ticker();
        private TextBox display;



    }
}

namespace Delegates
{
    using System.Collections;
    using System.Timers;
    using System.Windows.Forms;

    class Ticker
    {
        public delegate void Tick(int hh, int mm, int ss);

        public Ticker()
        {
            this.ticking.Elapsed += new ElapsedEventHandler(this.OnTimedEvent);
            this.ticking.Interval = 1000; // 1 second
            this.ticking.Enabled = true;
        }

        public void Add(Tick newMethod)
        {
            this.tickers += newMethod;
        }

        public void Remove(Tick oldMethod)
        {
            this.tickers -= oldMethod;
        }

        private void Notify(int hours, int minutes, int seconds)
        {
            if (this.tickers != null)
            {
                this.tickers(hours, minutes, seconds);
            }

        }

        private void OnTimedEvent(object source, ElapsedEventArgs args)
        {
            int hh = args.SignalTime.Hour;
            int mm = args.SignalTime.Minute;
            int ss = args.SignalTime.Second;
            Notify(hh, mm, ss);
        }

        private Tick tickers;
        private System.Timers.Timer ticking = new System.Timers.Timer();
    }
}