Question

I am researching Prism v2 by going thru the quickstarts. And I have created a WCF service with the following signature:

namespace HelloWorld.Silverlight.Web
{
[ServiceContract(Namespace = "http://helloworld.org/messaging")]
[AspNetCompatibilityRequirements(RequirementsMode =
                                 AspNetCompatibilityRequirementsMode.Allowed)]
  public class HelloWorldMessageService
  {
    private string message = "Hello from WCF";

    [OperationContract]
    public void UpdateMessage(string message)
    {
      this.message = message;
    }

    [OperationContract]
    public string GetMessage()
    {
      return message;
    }
  }
}

When I add a service reference to this service in my silverlight project it generates an interface and a class:

[System.ServiceModel.ServiceContractAttribute
        (Namespace="http://helloworld.org/messaging",
         ConfigurationName="Web.Services.HelloWorldMessageService")]
public interface HelloWorldMessageService {

  [System.ServiceModel.OperationContractAttribute
          (AsyncPattern=true,
      Action="http://helloworld.org/messaging/HelloWorldMessageService/UpdateMessage", 
ReplyAction="http://helloworld.org/messaging/HelloWorldMessageService/UpdateMessageResponse")]
    System.IAsyncResult BeginUpdateMessage(string message, System.AsyncCallback callback, object asyncState);

    void EndUpdateMessage(System.IAsyncResult result);

    [System.ServiceModel.OperationContractAttribute(AsyncPattern=true, Action="http://helloworld.org/messaging/HelloWorldMessageService/GetMessage", ReplyAction="http://helloworld.org/messaging/HelloWorldMessageService/GetMessageResponse")]
    System.IAsyncResult BeginGetMessage(System.AsyncCallback callback, object asyncState);

    string EndGetMessage(System.IAsyncResult result);
}

public partial class HelloWorldMessageServiceClient : System.ServiceModel.ClientBase<HelloWorld.Core.Web.Services.HelloWorldMessageService>, HelloWorld.Core.Web.Services.HelloWorldMessageService {
{
    // implementation
}

I’m trying to decouple my application by passing around the interface instead of the concrete class. But I’m having difficulty finding examples of how to do this. When I try and call EndGetMessage and then update my UI I get an exception about updating the UI on the wrong thread. How can I update the UI from a background thread?

---

I tried but I get UnauthorizedAccessException : Invalid cross-thread access.

string messageresult = _service.EndGetMessage(result);

Application.Current.RootVisual.Dispatcher.BeginInvoke(() => this.Message = messageresult );

The exception is thrown by Application.Current.RootVisual.

Answer 1

Just revisiting old posts left unanswered where I finally found an answer. Here’s a post I recently wrote that goes into detail about how I finally handled all this:

http://www.developmentalmadness.com/archive/2009/11/04/mvvm-with-prism-101-ndash-part-6-commands.aspx