Consume WCF service over TCP transport in Silverlight 4

This article describes how to consume Windows Communication Foundation (WCF) Service over Transmission Control Protocol (TCP) transport in Microsoft Silverlight 4.

Original product version:   Silverlight
Original KB number:   2425652


Silverlight 4 supports a netTcp transport binding element that gives us a new choice to implement duplex WCF. This code sample demonstrates how to consume netTcp WCF in Silverlight by creating a weather report subscription.

To demonstrate Silverlight accessing WCF, you may need a WCF service and a Silverlight WCF client. To create a weather report subscription application, follow these three steps:

Step 1: Create a Duplex WCF service with NetTcpBinding

  1. Create a new console project NetTcpWCFService. Then add a new WCF Service WeatherService to the project.

  2. Open an IWeatherService.cs file, run the following code to define the service contract:

     namespace NetTcpWCFService
        public interface IWeatherService
            [OperationContract(IsOneWay = true)]
            void Subscribe();
                [OperationContract(IsOneWay = true)]
            void UnSubscribe();
        public interface IWeatherServiceCallback
            void WeatherReport(string report);
  3. Open a WeatherService.cs file, use static event approach to implement subscription service. You first need to prefix the ServiceBehavior attribute to the existing WeatherService class, set an InstanceContext mode to a PerSession service. Then, run the following code to replace the default contents of the WeatherService class:

        public class WeatherService : IWeatherService
            static event EventHandler<WeatherEventArgs> WeatherReporting;
            IWeatherServiceCallback _callback;
            public void Subscribe()
                _callback = OperationContext.Current.GetCallbackChannel<IWeatherServiceCallback>();
                WeatherReporting += new EventHandler<WeatherEventArgs>(WeatherService_WeatherReporting);
            public void UnSubscribe()
                WeatherReporting -= new EventHandler<WeatherEventArgs>(WeatherService_WeatherReporting);
            void WeatherService_WeatherReporting(object sender, WeatherEventArgs e)
                // Remember check the callback channel's status before using it.
                if (((ICommunicationObject)_callback).State == CommunicationState.Opened)
        class WeatherEventArgs:EventArgs
            public string WeatherReport{set;get;}
  4. Create a separate thread to generate a mock weather report periodically. Run the following code to add the System.Threading namespace, in a static constructor of the WeatherService class:  

    static WeatherService()
            new WaitCallback(delegate
                string[] weatherArray = { "Sunny", "Windy", "Snow", "Rainy" };
                Random rand = new Random();
                while (true)
                    if (WeatherReporting != null)
                            new WeatherEventArgs
                                WeatherReport = weatherArray[rand.Next(weatherArray.Length)]
  5. To add a netTcpbinding endpoint to WCF service, run the following code to configure an app.config:

                <behavior name="NetTcpWCFService.WeatherServiceBehavior">
                    <serviceMetadata />
                    <serviceDebug includeExceptionDetailInFaults="false" />
            <service behaviorConfiguration="NetTcpWCFService.WeatherServiceBehavior"
                <endpoint address="" binding="netTcpBinding" bindingConfiguration="b1"
                  contract="NetTcpWCFService.IWeatherService" />
                <endpoint address="mex" binding="mexTcpBinding" contract="IMetadataExchange" />
                        <add baseAddress="net.tcp://localhost:4504/WeatherService" />
                    <binding name="b1">
                        <security mode="None"/>


    Only a few ports that are from 4502 to 4534 are allowed to be accessed by Silverlight, and you need a client access policy file to permit Silverlight access. For more information about how to permit Silverlight access, please refer to Step 3.

  6. Open a Program.cs file, add a namespace System.ServiceModel. Run the following code to start a ServiceHost service in Main method:

    static void Main(string[] args)
        using (var host = new ServiceHost(typeof(WeatherService)))
            Console.WriteLine("Service is running...");
            Console.WriteLine("Service address: "+host.BaseAddresses[0]);

Step 2: Create a Silverlight WCF client

Create a Silverlight application to consume the WCF. You need a button to subscribe or unsubscribe service, and a listbox to display the weather report from service.

  1. Create a new Silverlight project CSSL4WCFNetTcp. In the New Silverlight Application dialog box, you need to check the Host the Silverlight application in a new Web site checkbox, and then set the Silverlight Version to Silverlight 4.

  2. Run the following code to open a MainPage.xaml file and edit the default Grid element:

    <Grid x:Name="LayoutRoot" Background="White">
            <RowDefinition Height="46*" />
            <RowDefinition Height="26*" />
            <RowDefinition Height="228*" />
        <TextBlock Text="Silverlight NetTcp Sample" Grid.Row="0" Margin="0,0,0,10" FontSize="24"/>
        <StackPanel Orientation="Horizontal" Grid.Row="1">
            <Button Content="Subscribe weather report" Name="btnSubscribe" Click="Button_Click"/>
            <TextBlock VerticalAlignment="Center" FontStyle="Italic" Foreground="Red" Margin="5,0,0,0" Name="tbInfo"/>
        <ListBox Name="lbWeather" Grid.Row="2" Margin="0,5,0,0"/>
  3. Add a Service Reference to the weatherService class in WCF service. To do it, set the NetTcpWCFService project as a startup project, press Ctrl+F5 to start the service. Then, right-click the Silverlight project, select Add Service Reference option, in the Add Service Reference dialog box, input the weatherservice address, and press OK. And then, Visual studio 2010 generates WCF proxy code in Silverlight project.

  4. Run the following code to open the MainPage.xaml.cs file, and Initialize the WCF proxy in Loaded event:

    public partial class MainPage : UserControl,IWeatherServiceCallback
        public MainPage()
            Loaded += new RoutedEventHandler(MainPage_Loaded);
        bool _subscribed;
        WeatherServiceClient _client;
        void MainPage_Loaded(object sender, RoutedEventArgs e)
            _client = new WeatherServiceClient(
                new System.ServiceModel.InstanceContext(this));
            _client.SubscribeCompleted += _client_SubscribeCompleted;
            _client.UnSubscribeCompleted += _client_UnSubscribeCompleted;
        void _client_UnSubscribeCompleted(object sender, System.ComponentModel.AsyncCompletedEventArgs e)
            if (e.Error == null)
                _subscribed = false;
                btnSubscribe.Content = "Subscribe weather report";
                tbInfo.Text = "";
                tbInfo.Text = "Unable to connect to service.";
            btnSubscribe.IsEnabled = true;
        void _client_SubscribeCompleted(object sender, System.ComponentModel.AsyncCompletedEventArgs e)
            if (e.Error == null)
                _subscribed = true;
                btnSubscribe.Content = "UnSubscribe weather report";
                tbInfo.Text = "";
                tbInfo.Text="Unable to connect to service.";
            btnSubscribe.IsEnabled = true;
        // Display report when callback channel get called.
        public void WeatherReport(string report)
                new ListBoxItem
                    Content = string.Format("{0} {1}",DateTime.Now, report)
  5. Run the following code to add an event handler to handle button click event:

    private void Button_Click(object sender, RoutedEventArgs e)
        if (!_subscribed)
        btnSubscribe.IsEnabled = false;

Step 3: Deploying cross domain policy file

  1. Create an xml file clientaccesspolicy.xml, use the following code to configure content:

                    <domain uri="*"/>
                    <socket-resource port="4502-4506" protocol="tcp" />


    This file grants permissions to the Silverlight clients that are from any domain to access the server ports that are between 4502 to 4506.

  2. Find out the path of root physical directory (by default, C:\inetpub\wwwroot if you use IIS) of the server web site, place the policy file in the path.