What steps do I need to take to use WCF Callbacks?

Question

I am trying to learn WCF. I have a simple client and server application setup and upon pressing a button on the client, it gets an updated value from the server.

Answer 1

I know, old question... I came across this question from a google search earlier today and the answer provided by Ray Vernagus is the easiest to understand example of WCF that I have read to date. So much so that I was able to rewrite it in VB.NET without using any online converters. I thought I'd add the VB.NET variant of the example that Ray Vernagus provided. Just create a new VB.NET Windows Console application, add a reference to System.ServiceModel, and copy/paste the entire code below into the default Module1 class file.

Imports System.ServiceModel
Imports System.ServiceModel.Channels



Public Interface IMyContractCallback
     _
    Sub OnCallBack()
End Interface

 _
Public Interface IMyContract
     _
    Sub DoSomething()
End Interface

 _
Public Class Myservice
    Implements IMyContract

    Public Sub DoSomething() Implements IMyContract.DoSomething
        Console.WriteLine("Hi from server!")
        Dim callback As IMyContractCallback = OperationContext.Current.GetCallbackChannel(Of IMyContractCallback)()
        callback.OnCallBack()
    End Sub
End Class

Public Class MyContractClient
    Inherits DuplexClientBase(Of IMyContract)

    Public Sub New(ByVal callbackinstance As Object, ByVal binding As Binding, ByVal remoteAddress As EndpointAddress)
        MyBase.New(callbackinstance, binding, remoteAddress)
    End Sub
End Class

Public Class MyCallbackClient
    Implements IMyContractCallback

    Public Sub OnCallBack() Implements IMyContractCallback.OnCallBack
        Console.WriteLine("Hi from client!")
    End Sub
End Class


Module Module1

    Sub Main()
        Dim uri As New Uri("net.tcp://localhost")
        Dim binding As New NetTcpBinding()
        Dim host As New ServiceHost(GetType(Myservice), uri)
        host.AddServiceEndpoint(GetType(IMyContract), binding, "")
        host.Open()

        Dim callback As New MyCallbackClient()
        Dim client As New MyContractClient(callback, binding, New EndpointAddress(uri))
        Dim proxy As IMyContract = client.ChannelFactory.CreateChannel()

        proxy.DoSomething()
        ' Printed in console:
        '  Hi from server!
        '  Hi from client!

        Console.ReadLine()

        client.Close()
        host.Close()
    End Sub

End Module