Silverlight out-of-browser and initParams

Silverlight 3 supports a very cool 'deployment model' where you can run the Silverlight Application 'out-of-browser' (OOB) and kick it off from your start menu. It even works offline. This is the future, get to like it.

However, because the plug-in is no longer hosted in your page you lose all those juicy settings and, perhaps worst of all, you initialization parameters aren't available when the app runs OOB. This is frustrating because a lot of people pass in settings from their host web-application's web.config file using this very mechanism.

However, it only takes a little bit of code to work around this scenario by caching the initParams in isolated storage whenever the applicaiton is run in-browser. Here's some code that does just that:
private void Application_Startup(object sender, StartupEventArgs e)
{
    var mp = new MainPage();
this.RootVisual = mp;
    IDictionary<string, string> initParams = LoadInitParams(e);
// this just adds the init params to the MainPage for demo purposes only
foreach (var kv in initParams)
    {
        mp.LayoutRoot.Children.Add(new TextBlock { Text = kv.Key, FontStyle = FontStyles.Italic });
        mp.LayoutRoot.Children.Add(new TextBlock { Text = kv.Value, Margin = new Thickness(5,0,0,0) });
    }
}
private static IDictionary<string, string> LoadInitParams(StartupEventArgs e)
{
    IDictionary<string, string> initParams;
// if running out of browser retrieve 'initParams' from cache
if (Application.Current.IsRunningOutOfBrowser)
    {
using (IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication())
using (IsolatedStorageFileStream stream = new IsolatedStorageFileStream("initParams.txt", System.IO.FileMode.Open, isf))
        {
            DataContractSerializer ser = new DataContractSerializer(typeof(Dictionary<string, string>));
            initParams = (Dictionary<string, string>)ser.ReadObject(stream);
        }
    }
// otherwise write initParams to cache
else
    {
        initParams = e.InitParams;
using (IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication())
using (IsolatedStorageFileStream stream = new IsolatedStorageFileStream("initParams.txt", System.IO.FileMode.Create, isf))
        {
            DataContractSerializer ser = new DataContractSerializer(typeof(Dictionary<string, string>));
            ser.WriteObject(stream, initParams);
        }
    }
return initParams;
}
Easy peasy.

One recommendation here though is that you probably want a layer of indirection between Initalization Parameters and your 'silverlight configuration' in this case. The reason for this is the initParams will only get updated when you run the app in-browser. It's possible that your user will never run the app in-browser again. And even if the XAP gets updated your new parameters may never be seen, unless the app runs in-browser. So I'd recommend storing a static and constant URL in your initParameters that specifies an XML file (or web service) on the web server that contains your silverlight configuration.

You can then download this at will, even out-of-browser, whenever the network is available.

Originally posted by Josh Twist on 21 October 2009 here.