Reading XAML from a Silverlight Application Assembly

I was having dinner with Walt Ritscher tonight when he posed an interesting question: how can a Silverlight app load its own XAML from an application assembly?

I thought I knew the answer, because I had just finished doing a lot of research into the various ways to package code and resources in Silverlight 2.0. And I knew that the XAML files in a Silverlight 2.0 app get embedded as resources in the application assembly, which in turn gets embedded in the application package (the application’s XAP file). But when I got back to my hotel and tried it, it didn’t work. So I played around some and found the secret incantation.

Here’s the Page.xaml file in the test app that I wrote:

<UserControl x_Class=”SilverlightTestApp.Page”

    xmlns:x=”http://schemas.microsoft.com/winfx/2006/xaml”

    Width=”400″ Height=”300″>

    <Grid x_Name=”LayoutRoot” Background=”White”>

        <TextBlock x_Name=”Output” />

    </Grid>

</UserControl>

And here’s the output from the program:

Finally, here’s the code in Page.xaml.cs that produces the output by loading Page.xaml from the application assembly and assigning it to a TextBlock object:

StreamResourceInfo sri = Application.GetResourceStream

    (new Uri(“SilverlightTestApp;component/Page.xaml”, UriKind.Relative));

StreamReader reader = new StreamReader(sri.Stream);

Output.Text = reader.ReadToEnd();

The trick is to include “assemblyname;component” in the URI passed to GetResourceStream, even though the assembly you’re loading from is the application assembly and not a library assembly. Normally you don’t have to include the assembly name if you’re targeting the application assembly, but this is obviously an exception–at least in Beta 1.

I don’t know how useful this information is, but it ought to make a good icebreaker at a Silverlight party.