wcf中的使用全双工通信

wcf中的契约通信默认是请求恢复的方式，当客户端发出请求后，一直到服务端回复时，才可以继续执行下面的代码。

除了使用请求应答方式的通信外，还可以使用全双工。下面给出例子：

1.添加一个wcf类库

2.在服务契约添加如下一个片段

[ServiceContract(Namespace = "http://Microsoft.ServiceModel.Samples", SessionMode = SessionMode.Required,
        CallbackContract = typeof(ICalculatorDuplexCallback))]

public interface ICalculatorDuplex
   {
       [OperationContract(IsOneWay = true)]
       void Clear();
       [OperationContract(IsOneWay = true)]
       void AddTo(double n);
       [OperationContract(IsOneWay = true)]
       void SubtractFrom(double n);
       [OperationContract(IsOneWay = true)]
       void MultiplyBy(double n);
       [OperationContract(IsOneWay = true)]
       void DivideBy(double n);
   }

其中ICalculatorDuplexCallback为实现全双工客户端的接口

3.定义ICalculatorDuplexCallback接口。该接口目的主要是回调客户端的方法。和服务端无关，所以让该接口的方法设置为单向的

public interface ICalculatorDuplexCallback
{
    [OperationContract(IsOneWay = true)]
    void Equals(double result);
    [OperationContract(IsOneWay = true)]
    void Equation(string eqn);
}
4.由于回话是必须的，那么在契约实现的时候也要加上一个特性

  [ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession)]

public class Service1 : IService1
   {
       double result;
       string equation;
       ICalculatorDuplexCallback callback = null;

       public Service1()
       {
           result = 0.0D;
           equation = result.ToString();
           callback = OperationContext.Current.GetCallbackChannel<ICalculatorDuplexCallback>();
       }

       public void Clear()
       {
           callback.Equation(equation + " = " + result.ToString());
           result = 0.0D;
           equation = result.ToString();
       }

       public void AddTo(double n)
       {
           result += n;
           equation += " + " + n.ToString();
           callback.Equals(result);
       }

       public void SubtractFrom(double n)
       {
           result -= n;
           equation += " - " + n.ToString();
           callback.Equals(result);
       }

       public void MultiplyBy(double n)
       {
           result *= n;
           equation += " * " + n.ToString();
           callback.Equals(result);
       }

       public void DivideBy(double n)
       {
           result /= n;
           equation += " / " + n.ToString();
           callback.Equals(result);
       }
}

5.接着在项目中添加一个控制台程序，添加服务。服务会报异常

System.InvalidOperationException: 协定需要会话，但是绑定“BasicHttpBinding”不支持它或者因配置不正确而无法支持它。
   在 System.ServiceModel.Description.DispatcherBuilder.BuildChannelListener(StuffPerListenUriInfo stuff, ServiceHostBase serviceHost, Uri listenUri, ListenUriMode listenUriMode, Boolean supportContextSession, IChannelListener& result)
   在 System.ServiceModel.Description.DispatcherBuilder.InitializeServiceHost(ServiceDescription description, ServiceHostBase serviceHost)
   在 System.ServiceModel.ServiceHostBase.InitializeRuntime()
   在 System.ServiceModel.ServiceHostBase.OnOpen(TimeSpan timeout)
   在 System.ServiceModel.Channels.CommunicationObject.Open(TimeSpan timeout)
   在 Microsoft.Tools.SvcHost.ServiceHostHelper.OpenService(ServiceInfo info)

需要把服务端配置文件中的Binding换成

<endpoint address="" binding="BasicHttpBinding" contract="WcfServiceLibrary1.IService1">

<endpoint address="" binding="wsDualHttpBinding" contract="WcfServiceLibrary1.IService1">

6.在控制台端，添加服务引用，实现服务定义的ICalculatorDuplexCallback接口（该接口自动生成的对应到服务引用中的IService1Callback）

public class CallbackHandler : IService1Callback
  {
      public void Equals(double result)
      {
          Console.WriteLine("Result({0})", result);
      }

      public void Equation(string eqn)
      {
          Console.WriteLine("Equation({0})", eqn);
      }
  }

7.在main函数中，去调用服务

           InstanceContext instanceContext = new InstanceContext(new CallbackHandler());

            // Create a client
            ServiceReference1.Service1Client client = new ServiceReference1.Service1Client(instanceContext);

            Console.WriteLine("Press <ENTER> to terminate client once the output is displayed.");
            Console.WriteLine();

            // Call the AddTo service operation.
            double value = 100.00D;
            client.AddTo(value);

            // Call the SubtractFrom service operation.
            value = 50.00D;
            client.SubtractFrom(value);

            // Call the MultiplyBy service operation.
            value = 17.65D;
            client.MultiplyBy(value);

            // Call the DivideBy service operation.
            value = 2.00D;
            client.DivideBy(value);

            // Complete equation
            client.Clear();

            Console.ReadLine();

            //Closing the client gracefully closes the connection and cleans up resources
            client.Close();

8.运行结果

9.源码