c# - 当某事订阅事件/委托(delegate)时有什么方法可以得到通知？

Question

是否有任何方法可以在我的类(class)中订阅某个事件时收到通知，或者我是否需要在方法中包装订阅/取消订阅，例如:

public class MyClass : ISomeInterface
{
     public event SomeEventHandler SomeEvent; //How do I know when something subscribes?

     private void OnSomeEventSubscription(SomeEventHandler handler)
     { 
          //do some work
     }

     private void OnSomeEventUnsubscription(SomeEventHandler handler)
     { 
          //do some work
     }
}

代替

public class MyClass : ISomeInterface
{
     private SomeEventHandler _someEvent;

     public void SubscribeToSomeEvent(SomeEventHandler handler)
     {
          _someEvent += handler;

          //do some work
     }

     public void UnsubscribeFromSomeEvent(SomeEventHandler handler)
     {
          _someEvent -= handler;

          //do some work
     }    
}

我问的原因是因为事件已经直接暴露在 ISomeInterface 上，但是这个特定的实现需要知道什么时候订阅/取消订阅。

Answer 1

您可以为您的事件编写自定义访问器:

private SomeEventHandler _someEvent;
public event SomeEventHandler SomeEvent
{
    add
    {
        _someEvent += value;
        Console.WriteLine("Someone subscribed to SomeEvent");
    }
    remove
    {
        _someEvent -= value;
        Console.WriteLine("Someone unsubscribed from SomeEvent");
    }
}