To start, I will create a simple control that displays an image. This control will be packaged in a Silverlight class library DLL.

1. Open Visual Studio.

2. Create a new Silverlight application

3. Right click on the top node in your Solution Explorer. Choose  Add->New Project.

4. Select “Silverlight Class Library” and give it a name (mine is called TestCtrl). This project will create the DLL that will contain your control(s).

5. In your class library add a new a new Silverlight User Control (mine is called ImageTest).

6. Open up the XAML page (ImageTest.xaml) for this user control and add something like an Image control. If you are using a relative path to an image, make certain the image you reference is also included in your class library project.

<Image Source="scarlett.jpg"></Image> 

At this point your class library DLL is good to go. Build the and place it on your server in a location you can reference. Note that after building the DLL you will find it in your projects Bin\Debug folder. Clicking the “Show all Files” in the toolbar for your Solution Explorer will make this bin folder visible.

7. Next, proceed to your Silverlight Application opening up MainPage.xaml.cs

8. Add a reference to System.Reflection;

9. Use the WebClient class to download the DLL from the server. From the purpose of this demo, I have placed my test DLL at http://www.flaired.com/TestCtrl.dll 

private Assembly _testCtrl; 

public MainPage() 

{ 

    InitializeComponent(); 

    WebClient downloader = new WebClient(); 

    string path = "http://www.flaired.com/TestCtrl.dll"; 

    downloader.OpenReadCompleted += new OpenReadCompletedEventHandler 

      (downloader_OpenReadCompleted);  

    downloader.OpenReadAsync(new Uri(path, UriKind.Absolute)); 

} 

void downloader_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e) 

{ 

    AssemblyPart assemblyPart = new AssemblyPart(); 

    _testCtrl = assemblyPart.Load(e.Result); 

    UserControl control = (UserControl) 

    _testCtrl.CreateInstance("TestCtrl.ImageTest"); 

    LayoutRoot.Children.Add(control); 

}

10. Before you run this code, as a final step, make certain to have a ClientAccessPolicy.xml file located in the same location as your DLL. Silverlight will look for this file for permissions when making calls cross-domain. By default Silverlight only allows site-of -origin communication.

<?xml version="1.0" encoding="utf-8"?> 

<access-policy> 

  <cross-domain-access> 

    <policy> 

      <allow-from http-request-headers= "*"> 

        <domain uri="*"/> 

      </allow-from> 

      <grant-to> 

        <resource path="/" include-subpaths="true"/> 

      </grant-to> 

    </policy> 

  </cross-domain-access> 

</access-policy>

Demo:

[silverlight: Tip14_DLLLoading.xap]

Thank you,

–Mike