namespace DotNetEvents { using System; using System.Collections.Generic; // Define a class to hold custom event info public class CustomEventArgs : EventArgs { public CustomEventArgs(string s) { message = s; } private string message; public string Message { get { return message; } set { message = value; } } } // Class that publishes an event class Publisher { // Declare the event using EventHandler‹T› public event EventHandler‹CustomEventArgs› RaiseCustomEvent; public void DoSomething() { // Write some code that does something useful here // then raise the event. You can also raise an event // before you execute a block of code. OnRaiseCustomEvent(new CustomEventArgs("Did something")); } // Wrap event invocations inside a protected virtual method // to allow derived classes to override the event invocation behavior protected virtual void OnRaiseCustomEvent(CustomEventArgs e) { // Make a temporary copy of the event to avoid possibility of // a race condition if the last subscriber unsubscribes // immediately after the null check and before the event is raised. EventHandler‹CustomEventArgs› handler = RaiseCustomEvent; // Event will be null if there are no subscribers if (handler != null) { // Format the string to send inside the CustomEventArgs parameter e.Message += $" at {DateTime.Now}"; // Use the () operator to raise the event. handler(this, e); } } } //Class that subscribes to an event class Subscriber { private string id; public Subscriber(string ID, Publisher pub) { id = ID; // Subscribe to the event using C# 2.0 syntax pub.RaiseCustomEvent += HandleCustomEvent; } // Define what actions to take when the event is raised. void HandleCustomEvent(object sender, CustomEventArgs e) { Console.WriteLine(id + " received this message: {0}", e.Message); } } class Program { static void Main(string[] args) { Publisher pub = new Publisher(); Subscriber sub1 = new Subscriber("sub1", pub); Subscriber sub2 = new Subscriber("sub2", pub); // Call the method that raises the event. pub.DoSomething(); // Keep the console window open Console.WriteLine("Press Enter to close this window."); Console.ReadLine(); } } }