WPF to support hosting of Silverlight controls in vNext

To the great consternation of the blogosphere, Joe Stegman’s planned session on Silverlight quietly disappeared from the Microsoft PDC schedule, and no new announcements were made on that front. Instead we got a pre-recorded session from Rob Relyea entitled WPF Today and Tomorrow.

Microsoft adoption

Early on in his talk Rob reminded us that Microsoft is making the ultimate commitment to WPF in that many of their latest products are built on it, including the Expression Studio suite, Visual Studio, and most recently Web Matrix [see the demo in Rob’s talk]. He also hinted that there are other products on the way which cannot be announced yet.

As part of these efforts across Microsoft a number of controls have been developed which Rob feels would be widely applicable(one of which is WPF equivalent of the Silverlight ChildWindow) and he intends to work with the respective teams to release these components to the web.

Silverlight Integration

One welcome announcement Rob made was that the next version of WPF will support hosting of Silverlight controls [watch his demo]. Today, of course, this is somewhat possible by hosting a Web Browser inside WPF, then navigating it to some Silverlight content. What Rob announced was something deeper than that, in two ways. The first is that they want to enable good communication between the WPF host and the Silverlight components, including sharing data.

The second improvement was part of a bigger announcement: they are planning to solve the airspace issues with hosting embedded Hwnd content [watch]. This was something I didn’t expect – in fact, I thought the airspace issue was a problem here to stay.

To briefly recap what the airspace issue is: in current versions of WPF, whenever you need to embed Win32-based content inside WPF, the embedded content always ends up sitting on top of the WPF stuff. This is because Win32 Hwnds don’t layer well with WPF elements – they can’t share airspace. You also can’t rotate or scale the Hwnds or adjust their opacity like you can with WPF elements.

Rob announced that Microsoft will be making a large investment, and will remove the airspace restrictions. And I can see why it will be a large investment. From what Rob said [watch] it seems that they way they plan to tackle this is by rendering Hwnds off-screen so that their visuals can be composited into the appropriate place in the visual tree, then any keyboard our mouse input intended for the control will have to be redirected from the WPF surface back to the Hwnd. A tough challenge indeed – but with great rewards for anybody looking to port legacy applications.

Amongst other things that Microsoft are considering for WPF vNext, Rob mentioned the following:

• Proper support for Grouping in ItemsControls when doing UI Virtualization [watch]
• Improved support for data-binding to collections and properties that get updated in a background thread [watch]. For collections, this will involve adding APIs to allow the data-binding engine to interact with the locking scheme used in the collection.