An explicit conversion exists

An explicit conversion exists

• Timmy Lajaunie

  QueryCallbackContract callback = OperationContext.Current.GetCallbackChannel<QueryCallbackContract>();
  
  I don't know why but callback is null.
  Can anyone please explain that to me why there is no instance
  Thanks.
  
  [melack]
  
  

• cosmicstudio

  You will also need to set the CallbackContract property of the ServiceContractAttribute annotation.
  
  For example:
  
  [ServiceContract(CallbackContract=typeof(QueryCallbackContract))]
  public interface QueryContract
  {
  [OperationContract(IsOneWay = true)]
  void Query(string query);
  }

  
  public interface QueryCallbackContract
  {
  [OperationContract(IsOneWay = true)]
  void Response(string response);
  }
  

  
  -- Justin

  
  

• originsnone

  Hey!
  
  Now I have another problem. I get this error:
  Object reference not set to an instance of an object.
  
  service side:
  
  using (new OperationContextScope())
  {
  using (ChannelFactory<QueryContract> factory = new ChannelFactory<QueryContract>(binding, replyTo))
  {
  QueryCallbackContract callback = OperationContext.Current.GetCallbackChannel<QueryCallbackContract>();
  OperationContext.Current.OutgoingMessageHeaders.RelatesTo = messageId;
  
  
  callback.Response("bar"); //error
  
  }
  }
  
  [melack]
  
  
  

• Big Ticket

  It looks like QueryService is your Service, QueryCallbackContract is the callback contract (an interface), and Query is the interface method that has been annotated with OperationContract.

  If this is true, then getting sending a message back to the sender (client) is as follows:

  public void Query(String query){

  ...

  QueryCallbackContract callback = OperationContext.Current.GetCallbackChannel<QueryCallbackContract>();

  // you can then invoke the callback method

  ...

  }

  -- justin smith

  http://www.wintellect.com

  
  
  

• volkerm

  Hey!
  
  This is my code:
  
  
  Client:
  ------
  
  [ServiceContract]
  public interface QueryContract
  {
  [OperationContract(IsOneWay = true)]
  void Query(string query);
  }
  
  [ServiceContract]
  public interface QueryCallbackContract
  {
  [OperationContract(IsOneWay = true)]
  void Response(string response);
  }
  
  
  class QueryCallbackService : QueryCallbackContract
  {
  public void Response(string response)
  {
  UniqueId relatesTo = OperationContext.Current.IncomingMessageHeaders.RelatesTo;
  }
  }
  
  
  class Program
  {
  static void Main(string[] args)
  {
  CustomBinding binding = new CustomBinding(new TextMessageEncodingBindingElement(), new HttpTransportBindingElement());
  ChannelFactory<QueryContract> factory = new ChannelFactory<QueryContract>(binding, new EndpointAddress("http://localhost:8001/destination/"));
  QueryContract channel = factory.CreateChannel();
  
  using (new OperationContextScope())
  {
  OperationContext.Current.OutgoingMessageHeaders.ReplyTo = new EndpointAddress("http://localhost:8002/callback/");
  OperationContext.Current.OutgoingMessageHeaders.MessageId = new UniqueId();
  
  channel.Query("foo");
  
  }
  }
  }
  
  
  Service:
  --------
  
  [ServiceContract]
  public interface QueryContract
  {
  [OperationContract(IsOneWay = true)]
  void Query(string query);
  }
  
  [ServiceContract]
  public interface QueryCallbackContract
  {
  [OperationContract(IsOneWay = true)]
  void Response(string response);
  }
  
  
  class QueryService : QueryContract
  {
  
  public void Query(string query)
  {
  
  EndpointAddress replyTo = OperationContext.Current.IncomingMessageHeaders.ReplyTo;
  UniqueId messageId = OperationContext.Current.IncomingMessageHeaders.MessageId;
  CustomBinding binding = new CustomBinding(new TextMessageEncodingBindingElement(), new HttpTransportBindingElement());
  
  ChannelFactory<QueryContract> factory = new ChannelFactory<QueryContract>(binding, replyTo);
  
  using (new OperationContextScope())
  {
  QueryCallbackContract channel = OperationContext.Current.GetCallbackChannel<QueryCallbackContract>();
  OperationContext.Current.OutgoingMessageHeaders.RelatesTo = messageId;
  
  channel.Response("bar"); //ERROR: Object reference not set to an instance of an object
  }
  }
  
  }
  
  class Program
  {
  static void Main(string[] args)
  {
  using (ServiceHost serviceHost = new ServiceHost(typeof(QueryService)))
  {
  CustomBinding binding = new CustomBinding(new TextMessageEncodingBindingElement(), new HttpTransportBindingElement());
  serviceHost.AddServiceEndpoint(typeof(QueryContract), binding, "http://localhost:8001/destination/");
  serviceHost.Open();
  Console.WriteLine("Service Running - Press Any key to quit");
  Console.ReadLine();
  serviceHost.Close();
  }
  }
  }
  
  
  Thanks in advance.
  
  [melack]
  
  

• MrFaith

  It works now.
  If I look at the svctraceviewer tool I can see the [SOAP Message Header]:
  
  s:mustUnderstand 1
  a:Action http://tempuri.org/QueryContract/Query
  a:Address http://localhost:8004/reply
  a:MessageID urn:uuid:42a6a06e-77a1-4369-8162-d60b1783e7df
  s:mustUnderstand 1
  a:To net.tcp://localhost:8005/duplex
  
  and
  
  s:mustUnderstand 1
  a:Action http://tempuri.org/QueryContract/Response
  a:RelatesTo urn:uuid:42a6a06e-77a1-4369-8162-d60b1783e7df
  s:mustUnderstand 1
  a:To http://schemas.xmlsoap.org/ws/2004/08/addressing/role/anonymous
  
  Thanks.
  
  [melack]
  
  

• _cham

  Thanks, Justin.
  That's it.
  
  [melack]
  
  

• la

  What does the client look like Does it provide an instance of the callback contract before invoking the service

  For example, here "IServiceDuplexCallback" is the callback interface provided in metadata to the client when svcutil.exe generated the proxy. You have to create an instance of a class that implements that interface, then when you instantiate the proxy, provide it in the InstanceContext:

  CALLBACK INTERFACE IMPLEMENTATION

  class ServiceCallback : IServiceDuplexCallback

  {... class implementation }

  CODE TO INVOKE PROXY

  InstanceContext context = new InstanceContext(new ServiceCallback());

  ServiceDuplexProxy proxy = new ServiceDuplexProxy(context);

  
  
  
• An explicit conversion exists