WCF Callbacks between the Service and Client

Callbacks

WCF supports duplex communication between service and client also. In other words, service can also call a client's function to inform the client during an event. A callback contract must be defined, and client should implement that contract interface.

public interface IResult
{
  [OperationContract]
  void Result (int result);
}

Client needs to inform the WCF that it supports the callback. This is done when creating the ChannelFactory.

class Client : IResult
{
  public void Result (int result)
  {
    Console.WriteLine("Result = {0}", result);
  }

  public Client ()
  {
        NetTcpBinding netTcpBinding = new NetTcpBinding();

        Uri serviceUri = new Uri("http://localhost:9090/AdderService");

        IChannelFactory channelFactory = new DuplexChannelFactory(
            this, netTcpBinding);

        IAdder adder = channelFactory.CreateChannel(serviceUri);
  }
}

On the service side, the service gets the callback channel using the OperationContext's GetCallbackChannel method.

IResult resultCallback = OperationContext.Current.GetCallbackChannel();
resultCallback.Result(5);

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