Events

Events

An event is a delegate-based member that follows the publish/subscribe pattern — a class raises the event, and any number of external handlers can subscribe to react to it, without the publisher knowing who they are. Subscribers attach with += and the class raises the event internally by invoking it like a delegate. Events are how UI frameworks and many libraries notify code about state changes.

Note: An event can only be raised from inside its declaring class, even though outside code can subscribe to it.

Example: Events

using System;

class Button
{
    public event Action Clicked;

    public void Click()
    {
        Console.WriteLine("Button clicked!");
        Clicked?.Invoke();
    }
}

class Program
{
    static void Main(string[] args)
    {
        Button button = new Button();
        button.Clicked += () => Console.WriteLine("Handler: something happened");

        button.Click();
    }
}