silverlight 4, dynamically loading xap modules

Question

I know that it is possible to load xap modules dynamically using Prism or MEF framework. However, I'd like not to use those frameworks; instead load my xap files manually. So, I created the following class (adapted from internet):

public class XapLoader
{
    public event XapLoadedEventHandler Completed;

    private string _xapName;

    public XapLoader(string xapName)
    {
        if (string.IsNullOrWhiteSpace(xapName))
            throw new ArgumentException("Invalid module name!");
        else
            _xapName = xapName;
    }

    public void Begin()
    {
        Uri uri = new Uri(_xapName, UriKind.Relative);
        if (uri != null)
        {
            WebClient wc = new WebClient();
            wc.OpenReadCompleted += onXapLoadingResponse;
            wc.OpenReadAsync(uri);
        }
    }

    private void onXapLoadingResponse(object sender, OpenReadCompletedEventArgs e)
    {
        if ((e.Error == null) && (e.Cancelled == false))
            initXap(e.Result);

        if (Completed != null)
        {
            XapLoadedEventArgs args = new XapLoadedEventArgs();
            args.Error = e.Error;
            args.Cancelled = e.Cancelled;
            Completed(this, args);
        }
    }

    private void initXap(Stream stream)
    {
        string appManifest = new StreamReader(Application.GetResourceStream(
        new StreamResourceInfo(stream, null), new Uri("AppManifest.xaml",
                                       UriKind.Relative)).Stream).ReadToEnd();

        XElement deploy = XDocument.Parse(appManifest).Root;

        List<XElement> parts = (from assemblyParts in deploy.Elements().Elements()
                                select assemblyParts).ToList();

        foreach (XElement xe in parts)
        {
            string source = xe.Attribute("Source").Value;
            AssemblyPart asmPart = new AssemblyPart();
            StreamResourceInfo streamInfo = Application.GetResourceStream(
                 new StreamResourceInfo(stream, "application/binary"), 
                 new Uri(source, UriKind.Relative));
            asmPart.Load(streamInfo.Stream);
        }
    }
}

public delegate void XapLoadedEventHandler(object sender, XapLoadedEventArgs e);

public class XapLoadedEventArgs : EventArgs
{
    public Exception Error { get; set; }

    public bool Cancelled { get; set; }
}

The above code works fine; I can load any xap the following way:

XapLoader xapLoader = new XapLoader("Sales.xap");
xapLoader.Completed += new XapLoadedEventHandler(xapLoader_Completed);
xapLoader.Begin();

Now, I have a UserControl called InvoiceView in the Sales.xap project, so I would like to instantiate the class. In the current project (Main.xap) I added reference to Sales.xap project, however, since I load it manually I set "Copy Local = False". But when executed, the following code throws TypeLoadException:

Sales.InvoiceView view = new Sales.InvoiceView();

It seems the code can't find InvoiceView class. But I checked that XapLoader's initXap() method was successfully executed. So why the code can't find InvoiceView class? Can someone help me with this problem?

An easier way to do this is to use the Managed Extensibility Framework (MEF) that is built into Silverlight 4, in addition to .NET 4. — Chris Pietschmann

Gone Coding Gone Coding · Accepted Answer · 2010-09-09T08:21:43

This is based on the asker's self-answer below, rather than the question.

If you delete a project/module the output DLLs/XAP files do hang around. If you click the "show all files" button you will see some these left-over output files in your clientbin, bin and obj folders of related projects.

alt text

You can delete them individually from the project, or, when in doubt, search for all BIN and OBJ (e.g. using desktop explorer) and delete all those folders. The BIN/CLIENTBIN/OBJ folders will be recreated when needed (this the job that the "clean" option in Visual Studio should have done!)

Hope this helps.

silverlight 4, dynamically loading xap modules

4 Answers