Silverlight Projects

Dynamically load an .xap into a silverlight app

Visual studio solution, Live demo

(Update: You can also use XapLoader, a helper class for loading .xap files into silverlight apps)

This article shows how to dynamically load an .xap into a silverlight app.

Using this technique you can use create a small (< 10 KB) preloader application which shows a loading bar or some fancy animations while the user waits for the big main app.
Furthermore it enables you to divide a big silverlight app into some small ones which are dynamically loaded when they are needed.

The loading of the .xap file is done in two steps. First we download the .xap file from the server (some standard webclient stuff).

// "?t=" + DateTime.Now.Ticks.ToString() to prevent caching by browser
this.Uri = new Uri("ImagePresenter.xap?t=" + DateTime.Now.Ticks.ToString(), UriKind.RelativeOrAbsolute);
this.RootAssembly = "ImagePresenter.dll";
this.TypeName = "ImagePresenter.MainPage";

// Use WebClient to download the .xap file (and get the stream)
WebClient wc = new WebClient();
wc.DownloadProgressChanged += new DownloadProgressChangedEventHandler(wc_DownloadProgressChanged);
wc.OpenReadCompleted += new OpenReadCompletedEventHandler(wc_OpenReadCompleted);
wc.OpenReadAsync(this.Uri);

Then we use the following code to start the app.

this.Stream = e.Result;

// Get the stream of the manifest (which lists the dlls included in the .xap)
// see http://blogs.msdn.com/katriend/archive/2008/03/16/silverlight-2-structure-of-the-new-xap-file-silverlight-packaged-application.aspx
StreamResourceInfo manifestResourceInfo = Application.GetResourceStream(
     new StreamResourceInfo(this.Stream, null),
     new Uri("AppManifest.xaml", UriKind.Relative));

XmlReader reader = XmlReader.Create(manifestResourceInfo.Stream);
Assembly asm = null;
StreamResourceInfo assemblyStream = new StreamResourceInfo(this.Stream, "application/binary");

// Step through all .dlls
while (reader.Read())
{
     // If it's an assembly part...
     if (reader.IsStartElement("AssemblyPart"))
     {
          reader.MoveToAttribute("Source");
          reader.ReadAttributeValue();

          // ...get the stream
          StreamResourceInfo si = Application.GetResourceStream(assemblyStream, new Uri(reader.Value, UriKind.Relative));
          AssemblyPart p = new AssemblyPart();

          // If it's the main assembly,...
          if (reader.Value == this.RootAssembly)
          {
               // ...load it and remember it for later use
               asm = p.Load(si.Stream);
          }
          else
          {
               // Otherwise just load it
               p.Load(si.Stream);
          }
     }
}

if (asm == null)
{
     throw new InvalidOperationException("Could not find specified assembly.");
}

UIElement instance = asm.CreateInstance(this.TypeName) as UIElement;
if (instance == null)
{
     throw new InvalidOperationException("Could not create instance of requested type.");
}

// Host content in a contentPresenter
this.cpHost.Content = instance;