如何获取添加和删除块中的事件订阅者数量？ [英] How do I get the number of event subscribers in the add and remove blocks?

问题描述

如果我使用显式语法来声明一个事件，是否可以获得 中的订阅者数量 add {} 和删除{} 代码块？例如：

If I use the explicit syntax for declaring an event, is it possible to get the number of subscribers inside the add {} and remove {} code blocks? For example:

public event EventHandler MyEvent
{
    add
    {
        MyEvent += value;
        // Can I get a count of subscribers here?
    }
    remove
    {
        MyEvent -= value;
        // And also here?
    }
}

我的尝试：



我已经找到了在代码的其他部分执行此操作的方法，使用...

What I have tried:

I have found a way to do this in other parts of the code, using...

MyEvent.GetInvocationList().Count

...但是我无法弄清楚如何在事件声明代码中使用这种语法。

...but I can't figure out how or even if this syntax can be used inside the event declaration code.

推荐答案

这个怎么样？

How about this?

private EventHandler _myEvent;
private int _myEventSubscribersCount;

public event EventHandler MyEvent
{
    add
    {
        _myEvent += value;
        _myEventSubscribersCount = _myEvent.GetInvocationList().Length;
    }

    remove
    {
        _myEvent -= value;
        _myEventSubscribersCount = _myEvent.GetInvocationList().Length;
    }
}

您只能在创建事件的类中执行此操作：

You can only do it from within the class that creates the event:

public class MyClass
    {
    public event EventHandler MyEvent;
    protected virtual void OnMyEvent(EventArgs e)
        {
        EventHandler eh = MyEvent;
        if (eh != null)
            {
            eh(this, e);
            }
        }
    public int CountEvents()
        {
        return MyEvent.GetInvocationList().Length;
        }
    }
...
private void MyButton_Click(object sender, EventArgs e)
    {
    MyClass mc = new MyClass();
    mc.MyEvent += mc_MyEvent;
    Console.WriteLine(mc.CountEvents());
    mc.MyEvent += mc_MyEvent;
    Console.WriteLine(mc.CountEvents());

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