Using WCF to communicate over Windows service and Windows forms applications

Question

Currently, I have 2 solutions in Visual Studio 2017:

1. A Windows forms application
2. A Windows service application hosting a WCF service class library (.dll)

And I need to communicate between them, in a cyclic way, as followed by the image below. The numbers represent the order.

The problem is, I'm actually able to communicate between WF and WCF application by using the request-replay operation contract (represented by numbers 1 and 4). But I'm not sure how to acomplhish steps 2 and 3.

Code for WCF interface:

namespace SmithWcfService {
    [ServiceContract]
    public interface ISmithWcfService {
        [OperationContract]
        void SendRequest( ); //Operation called by Windows Forms
    }
}

Code for WCF interface implementation

namespace SmithWcfService {
    public class SmithWcfService : ISmithWcfService {
        public void SendRequest( ) {
            //Ok, now I need to call Windows service application
        }
    }
}

Code for Windows service

namespace SmithWindowsService {
    static class Program {
        static void Main( ) {
            ServiceBase[ ] ServicesToRun;
            ServicesToRun = new ServiceBase[ ] {
                new SmithWindowsService( )
            };
            ServiceBase.Run( ServicesToRun );
        }
    }
}

namespace SmithWindowsService {    
    public partial class SmithWindowsService : ServiceBase {
        private ServiceHost host;

        public SmithWindowsService( ) {
            InitializeComponent( );
        }

        protected override void OnStart( string[ ] args ) {
            host = new ServiceHost( typeof( SmithWcfService.SmithWcfService ) );
            host.Open( );
        }
    }
}

Answer 1

If the windows service hosts your WCF service, you can simply pass anything it needs (callbacks, values, settings) at service start. You could pass a method of the windows service as Func<Input2, Output3> that the WCF service should call.

Without your code it's hard to tell where you need to put it though. Normally, it goes into your custom ServiceHostFactory.

---

Example of service with callback:

namespace SmithWcfService 
{
    [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single)] 
    public class SmithWcfService : ISmithWcfService 
    {
        private Func<string, int> callback;

        public SmithWcfService(Func<string, int> callback)
        {
            this.callback = callback;
        }

        public void SendRequest() 
        {
            //Ok, now I need to call Windows service application:
            var output = this.callback("input");
        }
    }
}

Example of hosting:

namespace SmithWindowsService 
{    
    public partial class SmithWindowsService : ServiceBase 
    {
        private ServiceHost host;

        public SmithWindowsService( ) 
        {
            InitializeComponent( );
        }

        protected override void OnStart(string[] args) 
        {
            var instance = new SmithWcfService.SmithWcfService(this.SomeMethodYouWantToCallIn);
            host = new ServiceHost(instance, new Uri("your.url.com"));
            host.Open( );
        } 

        private int SomeMethodYouWantToCall(string data)
        {
            // do things...
        }
    }
}