问如何计算有多少侦听器连接到一个事件？

EN

MessageReceived?.GetInvocationList().Length

class A
{
   public event EventArgs<SyslogMessageEventArgs> MessageReceived;

   public int SubscribedClients
   {
       get {
         return (MessageReceived == null)
                ? 0
                : MessageReceived.GetInvocationList().Length
                ;
       }
   } 
}


void Main()
{
    A a = new A();
    if(a.SubscribedClients == 0)
    {
        a.MessageReceived += ...;
    }
}