這兩天翻了很多關于回調資料，后來才恍然大悟，貼上來說下解決方案。

1. 回調接口聲明

    public interface ICallback    {        [OperationContract(IsOneWay = true)] // 回調操作也必須One Way          void CallbackToClient(DateTime timestamp, string message);    }

2.回調使用

/// <summary>    /// 設置服務行為為單例模式,即所有客戶端共享一個服務實例    /// </summary>    [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single, ConcurrencyMode = ConcurrencyMode.Multiple)]    public class MyTagService : IService    {

           static List<ICallback> m_Callbacks = new List<ICallback>();

           public void AddMessage(string message)        {            m_Callbacks.ForEach(callback =>            {                if (((ICommunicationObject)callback).State == CommunicationState.Opened)                    callback.CallbackToClient(DateTime.Now, message);                else                    m_Callbacks.Remove(callback);            });

         }

       /// <summary>        /// read from plc and update local value        /// </summary>        /// <param name="plcTag">需要讀取PLC的變量</param>        /// <returns>無</returns>        public string Read_PLC_Tag(PLCTag tag)        {            string value=plc.TagValue(tag);            if (ServerMessageGot != null)            {                ServerMessageGot(this, new MessageReceiveEventArgs(DateTime.Now,tag.Address.ToString() + "-" + tag.DataSize.ToString() + "-" + value.ToString()));            }            AddMessage(tag.Address.ToString() + "-" + tag.DataSize.ToString() + "-" + value.ToString());     //回調                        return value;        }

    }

3. 回調事件

///<summary>      ///實現回調接口      ///</summary>       [CallbackBehavior(ConcurrencyMode = ConcurrencyMode.Multiple, UseSynchronizationContext = false)]    public class MyCallback : ICallback    {        /// <summary>          // 回調后觸發該事件，用于通知客戶端          /// </summary>           public event EventHandler<MessageReceiveEventArgs> ValueCallbacked = delegate { };        // 因為該方法是由服務器調用的          // 如果希望在客戶端能即時作出響應          // 應當使用事件          public void CallbackToClient(DateTime timestamp, string message)        {            MessageReceiveEventArgs e = new MessageReceiveEventArgs(timestamp,message);            if (this.ValueCallbacked != null)            {                this.ValueCallbacked(this, e);            }        }    }

4.客戶端回調

 public class Client     {        IService ClientChanel;        DuplexChannelFactory<IService> channelFactory;        MyCallback Callback = new MyCallback();                /// <summary>        /// 服務端對客戶端的消息通知        /// </summary>        public event EventHandler<MessageReceiveEventArgs> ServerMessageReceived = delegate { };        public Client(string ServerName)        {            NetTcpBinding binding = new NetTcpBinding();            binding.Security.Mode = SecurityMode.None;            InstanceContext instanceContext = new InstanceContext(Callback);            channelFactory = new DuplexChannelFactory<IService>(instanceContext, binding, new EndpointAddress("net.tcp://" + ServerName + ":2970/PLCTagServices/"));            ClientChanel=channelFactory.CreateChannel();            ClientChanel.Subscribe();            channelFactory.Faulted += new EventHandler(channelFactory_Faulted);                        Callback.ValueCallbacked+=new EventHandler<MessageReceiveEventArgs>(Callback_ValueCallbacked);        }                void Callback_ValueCallbacked(object sender,MessageReceiveEventArgs e)        {            ServerMessageReceived(this, e);        }

}