This session discussed how you can use ASP.NET AJAX controls and take advantage of Silverlight at the same time - creating a server control using the ASP.NET AJAX server control framework that uses Silverlight for its presentation.

There are several advantages to doing things like this - you can do this to slowly migrate a site to using Silverlight (one control at a time); you can separate the presentation of the control into code and XAML, giving more control to site designers; and it gives you new abilities using cross-platform vector graphics.

The meat of this presentation was code, so there’s not a lot of bullet-point style items to recount, but there were two controls shown using this technique. The first was a slideshow control that used Silverlight to show a nice transition when switching pictures in the slideshow; the second was a dynamic graph of stock prices that refreshed periodically.

The pattern for doing this is similar to that of creating other ASP.NET AJAX controls. To that end, both demos were done by deriving from the Xaml control that has a lot of base functionality and implements the proper AJAX script interface and saves you time when starting your own XAML based controls. The Xaml control is a part of ASP.NET Futures (so it’s not the base package yet but should be soon).

Basically there are three parts - write your XAML to handle the UI, set the XamlUrl property on the Xaml control so it knows how to display, and write the client script to work against the XAML tree. Obviously that’s pretty simplified, but it seems to me that the hard part really is working out the proper JavaScript to manipulate the XAML and intercept the events. ASP.NET AJAX seems to have a lot of helpers and convenience methods to make this easier, but if you’re not writing this in Orcas I can see where it’ll be a little slow to ramp up on.

I like the approach of writing controls using Silverlight. The ability to slowly migrate a site or individual functionality over to use Silverlight one control at a time is appealing. I can envision several charting or graphing applications I could use this sort of thing in.