David's Weblog

Here’s a tip for using the FlourineFX AMF interface with Silverlight, specifically the public void ResultReceived(IPendingServiceCall call) in the Fluorine Silverlight sample code. After you’ve received a response in your callback it will be running in a different thread. If you don’t use a thread safe way to access the UserControl then you might see the following:

A first chance exception of type ‘System.UnauthorizedAccessException’ occurred in System.Windows.dll. If you examine the details of the exception then you will see the following:

System.UnauthorizedAccessException: Invalid cross-thread access.

You need to make a call in the UI thread, but first you need access to it. Try the following. In App.xaml.cs, create a static class, variable and get/set methods for the dispatcher. On application startup, save the RootVisual.Dispatcher in that static variable.

App.xaml.cs

private void Application_Startup(object sender, StartupEventArgs e)
{
     UIThread.Dispatcher = RootVisual.Dispatcher;
}

/*
* Provide global access to to the UI thread.  Useful for callbacks that
* run in a different thread.
*/
public static class UIThread
{
     public static Dispatcher Dispatcher { get; set; }
}

Now, when you receive a callback in ResultReceived(IPendingServiceCall call) you can use:

App.UIThread.Dispatcher.BeginInvoke(() => _className.methodName());

to call a method in the UserControl you want to manipulate. Here is a helpful link that describes this topic in detail.