WCF学习之: IsInitiating 和 IsTerminating

       "IsInitiating=false" 表示执行该方法前，必须调用一个标注了 "IsInitiating=true" 的方法来创建 Session；而 "IsTerminating=true" 表示该方法调用结束后，WCF 将会释放服务对象，客户端代理将不能继续任何操作(除非我们创建一个新的代理)。IsInitiating 和 IsTerminating 只能用于启用了 Session 的服务对象上，缺省情况下 "IsInitiating=true, IsTerminating=false"。
      我们可以使用 IsInitiating 和 IsTerminating 来控制服务对象的流程和状态，比如使用 "IsInitiating=false" 强制客户端在调用订单服务的任何操作前，必须使用 "Init(IsInitiating=true)" 来获取一个唯一流水号，而一旦调用 "Process(IsTerminating=true)" 完成订单结算后，就不能再做任何处理。

[ServiceContract(SessionMode = SessionMode.Required)]
public interface IOrderService
{
  [OperationContract(IsInitiating = true)]
  void Init();
  [OperationContract(IsInitiating = false, IsTerminating = false)]
  void DoSomething();

  [OperationContract(IsInitiating = false, IsTerminating = true)]
  void Process();
}

[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession)]
public class OrderService : IOrderService
{
  public void Init()
  {
    Console.WriteLine("Init...");
  }

  public void DoSomething()
  {
    Console.WriteLine("DoSomething...");
  }

  public void Process()
  {
    Console.WriteLine("Process...");
  }
}

public class WcfTest
{
  public static void Test()
  {
    AppDomain.CreateDomain("Server").DoCallBack(delegate
    {
      ServiceHost host = new ServiceHost(typeof(OrderService),
        new Uri("http://localhost:8080/MyService"));
      host.AddServiceEndpoint(typeof(IOrderService), new WSHttpBinding(), "");
      host.Open();
    });

    //-----------------------

    IOrderService order = ChannelFactory<IOrderService>.CreateChannel(new WSHttpBinding(),
      new EndpointAddress("http://localhost:8080/MyService"));

    using (order as IDisposable)
    {
      order.Init();
      order.DoSomething();
      order.Process();
    }
  }
}

如何客户端不按照这个次序调用，则会触发异常。

错误1

IOrderService order = ChannelFactory<IOrderService>.CreateChannel(new WSHttpBinding(),
  new EndpointAddress("http://localhost:8080/MyService"));

using (order as IDisposable)
{
  //order.Init();
  order.DoSomething();
  order.Process();
}

异常

未处理 System.InvalidOperationException
  Message="The operation 'DoSomething' cannot be the first operation to be called because IsInitiating is false."

错误2

IOrderService order = ChannelFactory<IOrderService>.CreateChannel(new WSHttpBinding(),
  new EndpointAddress("http://localhost:8080/MyService"));

using (order as IDisposable)
{
  order.Init();
  order.DoSomething();
  order.Process();
  order.DoSomething();
}

异常

未处理 System.InvalidOperationException
  Message="This channel cannot send any more messages because IsTerminating operation 'Process' has already been called."

       原文：http://www.rainsts.net/article.asp?id=457