async callback z

public class StackOverflow_5979252
{
    [ServiceContract(Name = "IMessageCallback")]
    public interface IAsyncMessageCallback
    {
        [OperationContract(AsyncPattern = true)]
        IAsyncResult BeginOnMessageAdded(string msg, DateTime timestamp, AsyncCallback callback, object asyncState);
        void EndOnMessageAdded(IAsyncResult result);
    }
    [ServiceContract(CallbackContract = typeof(IAsyncMessageCallback))]
    public interface IMessage
    {
        [OperationContract]
        void AddMessage(string message);
    }
    [ServiceBehavior(IncludeExceptionDetailInFaults = true, ConcurrencyMode = ConcurrencyMode.Multiple)]
    public class Service : IMessage
    {
        public void AddMessage(string message)
        {
            IAsyncMessageCallback callback = OperationContext.Current.GetCallbackChannel<IAsyncMessageCallback>();
            callback.BeginOnMessageAdded(message, DateTime.Now, delegate(IAsyncResult ar)
            {
                callback.EndOnMessageAdded(ar);
            }, null);
        }
    }
    class MyClientCallback : IAsyncMessageCallback
    {
        public IAsyncResult BeginOnMessageAdded(string msg, DateTime timestamp, AsyncCallback callback, object asyncState)
        {
            Action<string, DateTime> act = (txt, time) => { Console.WriteLine("[{0}] {1}", time, txt); };
            return act.BeginInvoke(msg, timestamp, callback, asyncState);
        }

        public void EndOnMessageAdded(IAsyncResult result)
        {
            Action<string,DateTime> act = (Action<string,DateTime>)((System.Runtime.Remoting.Messaging.AsyncResult)result).AsyncDelegate;
            act.EndInvoke(result);
        }
    }
    static Binding GetBinding()
    {
        return new NetTcpBinding(SecurityMode.None);
    }
    public static void Test()
    {
        string baseAddress = "net.tcp://" + Environment.MachineName + ":8000/Service";
        ServiceHost host = new ServiceHost(typeof(Service), new Uri(baseAddress));
        host.AddServiceEndpoint(typeof(IMessage), GetBinding(), "");
        host.Open();
        Console.WriteLine("Host opened");

        InstanceContext instanceContext = new InstanceContext(new MyClientCallback());
        DuplexChannelFactory<IMessage> factory = new DuplexChannelFactory<IMessage>(instanceContext, GetBinding(), new EndpointAddress(baseAddress));
        IMessage proxy = factory.CreateChannel();
        proxy.AddMessage("Hello world");

        Console.Write("Press ENTER to close the host");
        Console.ReadLine();
        ((IClientChannel)proxy).Close();
        factory.Close();
        host.Close();
    }
}