using System;
using System.Collections.Generic;namespace EventExample
{// 定义事件数据public class DataReceivedEventArgs : EventArgs{public string Data { get; }public DataReceivedEventArgs(string data){Data = data;}}// 发布者类public class Publisher{// 定义事件public event EventHandler<DataReceivedEventArgs> DataReceived;// 模拟数据接收public void ReceiveData(string data){Console.WriteLine("Publisher: Receiving data...");OnDataReceived(data);}// 触发事件protected virtual void OnDataReceived(string data){try{DataReceived?.Invoke(this, new DataReceivedEventArgs(data));}catch (Exception ex){Console.WriteLine($"Error while notifying subscribers: {ex.Message}");}}}// 订阅者类public class Subscriber{private readonly string _name;public Subscriber(string name){_name = name;}// 处理事件的方法public void OnDataReceived(object sender, DataReceivedEventArgs e){if (e == null || string.IsNullOrEmpty(e.Data)){Console.WriteLine($"{_name} received empty data.");return;}Console.WriteLine($"{_name} received data: {e.Data}");}}class Program{static void Main(string[] args){// 创建发布者Publisher publisher = new Publisher();// 创建订阅者Subscriber subscriber1 = new Subscriber("Subscriber 1");Subscriber subscriber2 = new Subscriber("Subscriber 2");// 订阅事件publisher.DataReceived += subscriber1.OnDataReceived;publisher.DataReceived += subscriber2.OnDataReceived;// 模拟接收数据publisher.ReceiveData("Hello, World!");// 取消订阅publisher.DataReceived -= subscriber1.OnDataReceived;// 再次模拟接收数据publisher.ReceiveData("Goodbye, World!");Console.ReadLine();}}
}

1. 事件定义
首先，在 Publisher 类中定义了一个事件 DataReceived，它的类型是 EventHandler<DataReceivedEventArgs>。这意味着该事件可以传递一个 DataReceivedEventArgs 类型的参数，通常用于包含与事件相关的数据。

public event EventHandler<DataReceivedEventArgs> DataReceived;
2. 事件处理方法
在 Subscriber 类中定义了一个方法 OnDataReceived，这个方法将会作为事件处理程序（event handler）来处理 DataReceived 事件。当事件被触发时，OnDataReceived 方法会被调用，并接收事件的发出者（sender）和事件数据（DataReceivedEventArgs）作为参数。

public void OnDataReceived(object sender, DataReceivedEventArgs e)
{
    // 处理事件
}
3. 订阅事件
publisher.DataReceived += subscriber1.OnDataReceived; 这行代码的作用是将 subscriber1 的 OnDataReceived 方法注册为 publisher 的 DataReceived 事件的处理程序。具体的执行逻辑如下：

事件订阅：使用 += 运算符将 subscriber1.OnDataReceived 方法添加到 DataReceived 事件的事件处理列表中。这意味着，当 DataReceived 事件被触发时，所有订阅了该事件的方法（包括 subscriber1.OnDataReceived）都会被调用。
4. 事件触发
在 Publisher 类中，有一个方法 OnDataReceived，它会触发 DataReceived 事件。这个方法会检查是否有订阅者，并调用它们的事件处理方法：

protected virtual void OnDataReceived(string data)
{
    DataReceived?.Invoke(this, new DataReceivedEventArgs(data));
}
5. 事件处理
当调用 publisher.ReceiveData("Hello, World!"); 时，会触发 DataReceived 事件，导致 OnDataReceived 方法被调用。所有订阅了 DataReceived 事件的方法都会被执行。在这种情况下，subscriber1.OnDataReceived 将会被调用，并传入 publisher 作为 sender 和包含数据 "Hello, World!" 的 DataReceivedEventArgs 对象。

总结
publisher.DataReceived += subscriber1.OnDataReceived; 是将 subscriber1 的 OnDataReceived 方法注册为事件处理程序的过程。
当 DataReceived 事件被触发时，所有注册的处理程序（包括 subscriber1.OnDataReceived）会被依次调用，处理相关的事件数据。
这种机制使得发布者（Publisher）和订阅者（Subscriber）之间实现了松耦合的关系，发布者不需要知道具体的订阅者，只需触发事件即可。