Microsoft has released their February 2006 CTP WinFX runtime components. According to Tim Sneath, a Windows Vista Technical Evangelist, this release offers a number of major performance improvements and is API and/or feature complete. This said, "there shouldn't be any more breaking changes between now and RTM".
Here are the relevant links:
Thanks to Karsten Januszewski, here is a list of the major breaking changes surrounding this release:
1) The following XML namespace Uris are modified:
OLD
http://schemas.microsoft.com/winfx/avalon/2005
NEW
http://schemas.microsoft.com/winfx/2006/xaml/presentation
OLD
http://schemas.microsoft.com/winfx/xaml/2005
NEW
http://schemas.microsoft.com/winfx/2006/xaml
2) The syntax for mapping a CLR namespace to an XML namespace has changed. This is true for namespaces in the same assembly or different a different assembly. A Mapping Processing Instruction is no longer necessary.
Mapping PI for same assembly
OLD
<?Mapping XmlNamespace="local" ClrNamespace="MyCompany.MyProduct" ?>
<... xmlns:my="local" >
NEW
<... xmlns:my="clr-namespace:MyCompany.MyProduct" >
Mapping PI for different assembly
OLD
<?Mapping XmlNamespace="local" ClrNamespace="MyCompany.MyProduct" Assembly="someDLL" ?>
<... xmlns:my="local" >
NEW
<... xmlns:my="clr-namespace:MyCompany.MyProduct;assembly=someDLL" >
For fully specified assembly names, follow the syntax outlined here: http://msdn2.microsoft.com/en-us/library/system.reflection.assemblyname.aspx
3) Specifying columns and rows in Grids is now stricter.
OLD
<Grid>
<ColumnDefinition />
</Grid>.
NEW
<Grid>
<ColumnDefinitions>
<ColumnDefinition/>
</ColumnDefinitions>
</Grid>
4) Increased strictness with databinding such that binding statements must be set using attribute syntax.
OLD
<TextBox.Text>{Binding}</TextBox.Text>
NEW
Text = "{Binding}"
5) System.Windows.Serialization is now System.Windows.Markup
6) UserControl has changed to be a ContentControl. The FixedTemplate property has beenremoved.
OLD
<UserControl>
<UserControl.FixedTemplate>
<Grid>
</Grid>
</UserControl.FixedTemplate>
</UserControl>
NEW
<UserControl>
<Grid>
</Grid>
</UserControl>
7) Removing MediaElement.Player property, and the player methods of MediaPlayer onto MediaElement.
MediaElement myME;
OLD
myME.Player.Play();
NEW
myME.Play(); // new
8) Behavior change to media
In the Jan CTP, the following XAML would play the video file until the file ended, or until the MediaElement was GCd.
<MediaElement Source="a.wmv">
A MediaElement now stops when it is Unloaded by default.
If MediaElement is incorporated into a visual that does not propagate OnLoaded and Unloaded events (such as VisualBrush), it won't play automatically on Load. There are a number of work-around for this:
If you want to preserve the old behavior of MediaElement of starting to play at parse time rather than OnLoaded - <MediaElement Source="foo" UnloadedBehavior="Play"/>
If you want to use a Storyboard - <MediaElement UnloadedBehavior="Manual"/>
If you want to use code-behind - <MediaElement UnloadedBehavior="Manual"/>
9) In order to insert an XML data island into a XAML file, the XML source must be wrapped in an x:XData tag:
OLD
<XmlDataProvider x:Key="aXmlDP">
<Root xmlns="">
<Number type="int">333</Number>
</Root>
</XmlDataProvider>
NEW
<XmlDataProvider x:Key="aXmlDP">
<x:XData>
<Root xmlns="">
<Number type="int">333</Number>
</Root>
</x:XData>
</XmlDataProvider>
10) VideoDrawing is broken in this build.
11) SinglePageViewer is now FlowDocumentPageViewer
12) The relative ource binding syntax has changed
OLD
{Binding Path=foo, RelativeSource=/TemplatedParent}
NEW
{Binding Path=foo, RelativeSource='{RelativeSource TemplatedParent}'}