gistfile1.cs

    internal class ChatMessageHandler<TMessage> : INotificationHandler<TMessage> where TMessage : ChatMessage
    {
        /// <summary>
        /// The callbacks invoked when the handler processes the messages.
        /// </summary>
        private Action<TMessage, ISubscription> callback;

        /// <summary>
        /// The conditions that must be met in order to fire the callbacks.
        /// </summary>
        private Func<TMessage, bool> condition;

        /// <summary>
        /// Registers a callback for when a chat message is published by the MessageCenter
        /// </summary>
        /// <param name="processor">The message.</param>
        /// <returns></returns>
        public void Register(
            Action<TMessage, ISubscription> processor,
            Func<TMessage, bool> condition)
        {
            this.callback = processor;
            this.condition = condition;
        }

        /// <summary>
        /// Unsubscribes the handler from notifications. This cleans up all of the callback references and conditions.
        /// </summary>
        public void Unsubscribe(INotificationCenter notificationCenter)
        {
            this.callback = null;
            this.condition = null;

            // Let the notification manager know we are unsubscribing.
            notificationCenter.Unsubscribe<TMessage>(this);
        }

        /// <summary>
        /// Processes the message by verifying the callbacks can be invoked, then invoking them.
        /// </summary>
        /// <param name="message">The message.</param>
        public void ProcessMessage(TMessage message)
        {
            if (!CanProcess(message))
            {
                return;
            }

            Post(message);
        }

        /// <summary>
        /// Determines whether this instance can post notifications with the specified message.
        /// </summary>
        /// <param name="message">The message.</param>
        /// <returns></returns>
        private bool CanProcess(TMessage message)
        {
            // If any of the conditions fail, don't process.
            return this.condition(message);
        }

        /// <summary>
        /// Posts the specified message as a notification to the callback.
        /// </summary>
        /// <param name="message">The message.</param>
        private void Post(TMessage message)
        {
            this.callback(message, this);
        }
    }