gistfile1.cs

    public abstract class ChatMessage : MessageBase<string>
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="ChatMessage"/> class.
        /// </summary>
        /// <param name="message">The message.</param>
        public ChatMessage(string message)
        {
            this.Message = message;
        }

        /// <summary>
        /// Gets the message.
        /// </summary>
        public string Message { get; private set; }
    }
    
        public class WhisperMessage : ChatMessage
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="WhisperMessage"/> class.
        /// </summary>
        /// <param name="message">The message.</param>
        /// <param name="target">The target.</param>
        public WhisperMessage(string message, ICharacter target) : base(message)
        {
            this.Target = target;
        }

        /// <summary>
        /// Gets the target that this message is intended for.
        /// </summary>
        public ICharacter Target { get; private set; }

        public override string GetContent()
        {
            return base.GetContent<string>();
        }
    }
    
    ### Usage
    
            public void Test()
        {
            var notification = new NotificationManager();
            var handler = new ChatMessageHandler<WhisperMessage>();

            handler.Register((msg, sub) =>
            {
                if (string.IsNullOrEmpty(msg.Content))
                {
                    sub.Unsubscribe(notification);
                }
            }, null);
            notification.Subscribe<WhisperMessage>(handler);
        }