using System;

using System.Threading.Tasks;

​

namespace WindowsFormsApp3

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }

        private void button1_Click(object sender, EventArgs e)

        {

            var c = new Calculator();

​

            // hook methods onto the NewResultFound event

            c.NewResultFound += OnNewResultFound;

            c.NewResultFound += OnNewResult;

​

            c.StartCalculationAsync();

        }

​

        void OnNewResultFound(Calculator sender, CalculatorEventArgs e)

        {

            label1.Text = e.Result.ToString();

        }

​

        void OnNewResult(Calculator sender, CalculatorEventArgs e)

        {

            label2.Text += ".";

        }

    }

    // Here the Calculator begins

    // delegate for all event handler (methods that are hooked to the event)

    delegate void CalculatorEventHandler(Calculator sender, CalculatorEventArgs e);

​

    // event arguments provided by the Calculator (should inherit from EventArgs)

    class CalculatorEventArgs : EventArgs

    {

        public int Result { get; set; }

    }

​

    class Calculator

    {

        // public event other classes can hook to

        public event CalculatorEventHandler NewResultFound;

​

        public async Task StartCalculationAsync()

        {

            Random r = new Random();

​

            while (true)

            {

                await Task.Delay(1000);     // complex calculation

                int result = r.Next(0, 1000);

​

                // create event arguments

                var e = new CalculatorEventArgs() { Result = result };

​

​

                // check if there are hooked methods and fire the event

                //if(NewResultFound != null)

                //    NewResultFound(this, e);

​

                // shorter way to safely fire the event

                NewResultFound?.Invoke(this, e);

            }

        }

    }

}

​