Of logical and visual trees in WPF

logical and visual trees in Silverlight

CuriousProgrammer — Sat, 24 May 2008 10:07:29 GMT

Should I be concerned that Silverlight does not make the same distinction between logical and visual trees? What compatibility issues will pop up down the road?

Link Listing - May 26, 2008

Christopher Steen — Tue, 27 May 2008 15:26:09 GMT

ASP.NET Ending a Response without Response.End() Exceptions? [Via: Rick Strahl ] UFrame: div meets...

re: Of logical and visual trees in WPF

gmurray — Tue, 27 May 2008 23:40:51 GMT

I've seen several instances with 3rd party controls where the visual parent chain is broken. I'll try to use VisualTreeHelper to navigate up the VTree and will get nothing before I reach the top. What causes this?

re: logical and visual trees in Silverlight

MikeHillberg — Thu, 29 May 2008 23:57:46 GMT

You mostly don't have to be concerned about it.

We haven't added the logical tree into Silverlight, because Silverlight mostly doesn't encounter the situations that motivate it. For example, one of the motivations for the logical tree is name lookup, primarily for ElementName bindings (e.g. "{Binding ElementName=textBlock1}"). But Silverlight doesn't support ElementName bindings, so the motivation isn't there.

A place where it does show up in Silverlight, though, is the Parent property. Currently in the Silverlight 2.0 beta, the FrameworkElement.Parent property returns the visual parent rather than a logical parent. We're investigating the best way to address that incompatibility.

re: Of logical and visual trees in WPF

MikeHillberg — Fri, 30 May 2008 00:14:19 GMT

Re this comment:

"I've seen several instances with 3rd party controls where the visual parent chain is broken. I'll try to use VisualTreeHelper to navigate up the VTree and will get nothing before I reach the top. What causes this?"

The most common situation for that is the case where the visual tree hasn't been set up yet. Take this markup, for example:

... When this is first parsed, the TextBlock is a logical child of the Button, but it's not a visual descendent yet. It becomes a visual descendent when the Button's control template is applied. That typically happens on the first layout (or if you explicitly call ApplyTemplate).