C# Unicast Event: ensure an event has only one subscriber with the use of GetInvocationList

Events in c# are designed for multicasting: one publisher for many subscribers. Limiting the number of subscribers may seeem an anti-pattern but in some cases may come in handy.
Here is a simple implementation of an event that limits to one the number of subscribers.

 public class ClassThatFiresEvents  
   {  
     public Action _myAction;  
     public event Action MyUnicastEvent  
     {  
       add  
       {  
         if (_myAction != null)  
         {  
           var invList = _myAction.GetInvocationList();  
           foreach (var ev in invList)  
           {  
             _myAction -= (Action)ev;  
           }  
         }  
         _myAction += value;  
       }  
       remove  
       {  
         _myAction -= value;   
       }  
     }  
     public void TriggerFromOutside()  
     {   
       if (_myAction != null)  
         _myAction();  
     }  
   }   

The code for testing this class:

  static void Main(string[] args)  
     {  
       ClassThatFiresEvents c = new ConsoleApplication1.ClassThatFiresEvents();  
       c.MyUnicastEvent += Method1;  
       c.MyUnicastEvent += Method2;  
       c.MyUnicastEvent += () => { Console.WriteLine("Anon 1"); };  
       c.MyUnicastEvent += () => { Console.WriteLine("Anon 2"); };  
       c.TriggerFromOutside();  
     }  
     private static void Method1() { Console.WriteLine("Method1"); }  
     private static void Method2() { Console.WriteLine("Method2"); }  

The Output is:

Anon 2