Services
Technology Web App Development Mobile App Development Windows App Development Database Development UI/UX Development Cloud Development SEO Digital Marketing Guest Posting Content Writing Artificial Intelligence Data Science ERP Development CRM Development CMS Development LMS Development Business Listing Blockchain Technology Startup Promotion AI Tools Integration
Products
Data Converter Cleaner TUC - Unit Converter Import Export Survey Manager Tweet Controller
Developer
Article Blog Forum Interview Beginner News Startup Quiz
Users
Career
Apply Job Internship
Pricing
Login Sign Up Get a Quote

interview

Home Interviews How does WCF support duplex communication? – MindStick
Ask Question

1 Answers

ICSM Computer
ICSM Computer 28 May 2025
Report Abuse

WCF supports duplex communication using a callback contract, enabling two-way communication between a service and its client. This is useful for scenarios like chat applications, real-time notifications, or event-based systems.

How Duplex Communication Works in WCF

  1. Client calls the service
  2. Service holds a reference to the client’s callback
  3. Service calls back the client asynchronously

Key Components

Component Description
ServiceContract The main service interface
CallbackContract An interface that defines operations the client must implement
InstanceContextMode Usually set to PerSession to maintain the callback reference
binding Must support sessions (e.g., NetTcpBinding, WSDualHttpBinding)

Example

1. Define Callback Contract

public interface IMyCallback
{
    [OperationContract(IsOneWay = true)]
    void OnNotify(string message);
}

2. Define Service Contract with Callback

[ServiceContract(CallbackContract = typeof(IMyCallback))]
public interface IMyService
{
    [OperationContract]
    void Register();

    [OperationContract]
    void SendMessage(string msg);
}

3. Implement the Service

[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession)]
public class MyService : IMyService
{
    public void Register()
    {
        var callback = OperationContext.Current.GetCallbackChannel<IMyCallback>();
        callback.OnNotify("Registered successfully.");
    }

    public void SendMessage(string msg)
    {
        var callback = OperationContext.Current.GetCallbackChannel<IMyCallback>();
        callback.OnNotify("Server received: " + msg);
    }
}

4. Create Client with Callback Implementation

public class MyClientCallback : IMyCallback
{
    public void OnNotify(string message)
    {
        Console.WriteLine("Received from server: " + message);
    }
}

5. Connect Client

var instanceContext = new InstanceContext(new MyClientCallback());
var client = new MyServiceClient(instanceContext); // auto-generated proxy
client.Register();
client.SendMessage("Hello from client");

Required Bindings for Duplex

Binding Supports Duplex? Notes
NetTcpBinding Yes Best for intranet scenarios
WSDualHttpBinding Yes Allows duplex over HTTP (complex setup)
NetNamedPipeBinding Yes For on-machine communication
BasicHttpBinding NO No duplex support
MindStick Training
Markdown for AI

A clean, structured version of this page for AI assistants and LLMs.

Open .md