Question

I am currently developing a WCF duplex service and I am trying to implement the callback method in my client app however there is a error of

'App.CallbackHandler' does not implement interface member IPostingServiceCallback.retrieveNotification(Service.Posting)' 

the service contract for my service are as follow

[ServiceContract(SessionMode=SessionMode.Required , CallbackContract = typeof(IPostingServiceCallBack))]
public interface IPostingService
{
    [OperationContract(IsOneWay = true)]
    void postNotification(Posting post);
}

public interface IPostingServiceCallBack
{
    [OperationContract]
    String retrieveNotification(Posting post);
}

I have generated the proxy and added into the project file of my client and adding the endpoint address into the app.config.

EDIT

The code I have in my client app currently is

public class CallBackHandler : IPostingServiceCallback
{
    public void retrieveNotification()
    {
        //planning to do something
    }
}

Answer 1

Your client application needs to implement IPostingServiceCallBack and define the retrieveNotification method.

Say you have a client (not the proxy) that will be consuming your duplex service:

public class MyClient : IPostingServiceCallBack
{

    public String retrieveNotification(Posting post)
    {

       // Implement your logic here
    }
}

Note the above is a bare-bones example as a simple illustration. Your client will probably derive from another class as well (depending on whether it’s ASP.NET, WinForms, WPF, etc).

Updated

You’re still not implementing the method. Your callback interface is:

public interface IPostingServiceCallBack
{
    [OperationContract]
    String retrieveNotification(Posting post);
}

Your implementation is:

public class CallBackHandler : IPostingServiceCallback
{
    public void retrieveNotification()
    {
        //planning to do something
    }
}

You have public void retrieveNotification(), whereas the interface has String retrieveNotification(Posting post). The method signatures don’t match.

You need to do:

public class CallBackHandler : IPostingServiceCallback
{
    public String retrieveNotification(Posting post)
    {
        // planning to do something
    }
}