Question

I am creating a Silverlight 2 user interface to a remote instrument. There are two concurrent users at different sites interacting with the instrument (operator at the instrument and remote scientist) and any number of observer users not interacting with it, just watching. However, whenever one of the two active users changes something these changes must be immediately reflected in the UIs of all users, e.g. panning or zooming an image or annotating or selecting part of an image, adding items to a collection displayed in a listbox. Within the client I use observable collections which easily reflect changes made by that user, but it is harder seeing changes made by another user. I can poll for changes from each client but something like push notifications would be better. I have extensively Googled for examples but not found anything which is quite what I need. There are all sorts of security issues with Silverlight interacting with WCF services which mean many potential examples just don’t work. I have essentially run out of time on this project and need help fast. Does anyone have any suggestion of a suitable simple example which illustrates how to do this? I am an experienced developer but have had to teach myself Silverlight and WCF services and there is noone in my area who knows anything about these. Even tho’ I have done a fair amount of ASP.NET work I am not a web/Javascript guru. Thanks.

Answer 1

Push notification is supported in Silverlight 2 using the new WCF PollingDuplexHttpBinding support. There are two assemblies installed with the Silverlight SDK (one for Silverlight app one for WCF server).

I have a few blog posts and a full sample application that demonstrate how to ‘push’ Stock updates from a Console Application server that self-hosts a WCF service to connected clients. It also shows how each client can add notes against a Stock and have those notes synchronized (pushed from server) to all other connected clients.

The latest version of the sample (Part 4) shows how to synchronize pushed updates between both Silverlight and WPF clients using two server endpoints as follows:

using System; using System.ServiceModel; using System.ServiceModel.Description;  namespace StockServer {     public class StockServiceHost : ServiceHost     {         public StockServiceHost(object singletonInstance, params Uri[] baseAddresses)             : base(singletonInstance, baseAddresses)         {         }          public StockServiceHost(Type serviceType, params Uri[] baseAddresses)             : base(serviceType, baseAddresses)         {         }          protected override void InitializeRuntime()         {             this.AddServiceEndpoint(                 typeof(IPolicyProvider),                 new WebHttpBinding(),                 new Uri('http://localhost:10201/')).Behaviors.Add(new WebHttpBehavior());              this.AddServiceEndpoint(                 typeof(IStockService),                 new PollingDuplexHttpBinding(),                 new Uri('http://localhost:10201/SilverlightStockService'));              this.AddServiceEndpoint(                 typeof(IStockService),                 new WSDualHttpBinding(WSDualHttpSecurityMode.None),                 new Uri('http://localhost:10201/WpfStockService'));              base.InitializeRuntime();         }     } } 

WPF clients connect to the WSDualHttpBinding endpoint and Silverlight clients connect to the PollingDuplexHttpBinding endpoint of the same WCF service. The app also shows how to handle the Silverlight client access policy requirements.

Clients (Silverlight or WPF) can add notes against a Stock in their UI and these notes propagate back to the server to be pushed to all other clients. This demonstrates communication in either direction and hopefully performs all of the necessary communication required for your app.

You can see a screenshot of the demo application running here.