How do I unsubscribe all handlers from an event for a particular class in C#?

Question

Basic premise:

I have a Room which publishes an event when an Avatar "enters" to all Avatars within the Room. When an Avatar leaves the Room I want it to remove all subscriptions for that room.

How can I best unsubscribe the Avatar from all events in the room before I add the Avatar to a new Room and subscribe to the new Room's events?

The code goes something like this:

class Room
{
   public event EventHandler<EnterRoomEventArgs> AvatarEntersRoom;
   public event EvnetHandler<LeaveRoomEventArgs> AvatarLeavesRoom;
   public event EventHandler<AnotherOfManyEventArgs> AnotherOfManayAvatarEvents;


   public void AddPlayer(Avatar theAvatar)
   {
      AvatarEntersRoom(this, new EnterRoomEventArgs()); 

      AvatarEntersRoom += new EventHandler<EnterRoomEventArgs>(theAvatar.HandleAvatarEntersRoom);

      AvatarLeavesRoom += new EventHandler<EnterRoomEventArgs>(theAvatar.HandleAvatarEntersRoom);

      AnotherOfManayAvatarEvents += new EventHandler<EnterRoomEventArgs>(theAvatar.HandleAvatarEntersRoom);          

   }

}

class Avatar
{
   public void HandleAvatarEntersRoom(object sender, EnterRoomEventArgs e)
   {
       Log.Write("avatar has entered the room");
   }

   public void HandleAvatarLeaveRoom(object sender, LeaveRoomEventArgs e)
   {
       Log.Write("avatar has left room");
   }

   public void HandleAnotherOfManayAvatarEvents(object sender, AnotherOfManyEventArgs e)
   {
       Log.Write("another avatar event has occurred");
   }
}

Answer 1

Each delegate has a method named GetInvocationList() that returns all the actual delegates that have been registered. So, assuming the delegate Type (or event) is named say MyDelegate, and the handler instance variable is named myDlgHandler, you can write:

Delegate[] clientList = myDlgHandler.GetInvocationList();
foreach (var d in clientList)
       myDlgHandler -= (d as MyDelegate);

to cover the case where it might be null,

 if(myDlgHandler != null)
  foreach (var d in myDlgHandler.GetInvocationList())
       myDlgHandler -= (d as MyDelegate);

Answer 2

Probably the simplest way to accomplish this would be to store all of your subscribed events for an avatar in an ArrayList of delegates to the events.

When the avatar leaves the room, simply loop through the list of delegates performing a standard remove (-=).

Answer 3

Is there anything wrong with a standard remove?

public void RemovePlayer(Avatar theAvatar) {
 AvatarEntersRoom -= new EventHandler<EnterRoomEventArgs>(theAvatar.HandleAvatarEntersRoom);

}

EDIT

Based on your update it appears that you want code that will remove a particular object from all events on a particular class. There is no realistic way to accomplish this goal. It's often a bit verbose but the best way is to individually add/remove a particular object method combo from every event.

The only way to get close to this functionality is to use reflection. You could reflectively grab all events on your class and then do some magic to find all instances of a class within the event chain. This will only be a partial solution though because it will ignore such things as a lambda expression event handlers.