委托与事件底层原理

1. 委托本质

delegate int MyDelegate(string s);

编译为继承 System.MulticastDelegate 的类：

class MyDelegate : MulticastDelegate {
    public extern int Invoke(string s);
    public extern IAsyncResult BeginInvoke(string s, AsyncCallback cb, object state);
    public extern int EndInvoke(IAsyncResult result);
}

2. 多播委托

MyDelegate d1 = s => s.Length;
MyDelegate d2 = s => int.Parse(s);
MyDelegate combined = d1 + d2;  // InvocationList 包含两个委托

3. 事件本质

public event EventHandler<string> OnMessage;

编译为：

private EventHandler<string> _onMessage;
public event EventHandler<string> OnMessage {
    add => Delegate.Combine(ref _onMessage, value);
    remove => Delegate.Remove(ref _onMessage, value);
}

4. 委托 vs 事件