using System;

​

// 1. 定义自定义事件参数类

public class MyEventArgs : EventArgs

{

    public string EventMessage { get; }

​

    public MyEventArgs(string message)

    {

        EventMessage = message;

    }

}

​

// 2. 声明包含事件的类

public class EventPublisher

{

    // 3. 声明事件

    public event EventHandler<MyEventArgs> MyEvent;

​

    // 4. 触发事件的方法

    public void RaiseEvent(string message)

    {

        Console.WriteLine("EventPublisher: Event is about to be raised.");

        MyEvent?.Invoke(this, new MyEventArgs(message));

    }

}

​

// 5. 声明事件处理器类

public class EventSubscriber

{

    // 6. 事件处理器

    public void HandleEvent(object sender, MyEventArgs e)

    {

        Console.WriteLine($"EventSubscriber: Event handled - {e.EventMessage}");

    }

}

​

class Program

{

    static void Main(string[] args)

    {

        // 创建事件发布者和事件订阅者

        EventPublisher publisher = new EventPublisher();

        EventSubscriber subscriber = new EventSubscriber();

​

        // 7. 订阅事件

        publisher.MyEvent += subscriber.HandleEvent;

​

        // 8. 触发事件

        publisher.RaiseEvent("Hello from the event!");

​

        // 9. 取消订阅事件

        publisher.MyEvent -= subscriber.HandleEvent;

​

        // 再次触发事件，但不会有订阅者响应

        publisher.RaiseEvent("Event without subscribers.");

​

        Console.ReadLine();

    }

}

​