FrameworkElement overlay notification?

Hi all,

Is there a way to receive an event notification when some other element
in a visual tree overlays the current element? For example, I have a
grid with a TextBlock in it. At runtime another textblock gets inserted
into the visual tree directly overlaying the existing box (or at least a
portion of it). Is there some event that we can hook into when part of
the tree is covered up?

I'm trying to figure this out for translucency type issues. I want to
adjust the Opacity value of this box when it is covered up. Even
better, is there some way to indicate that when a particular visual
element is in the tree, to change the opacity of the entire area
underneath that element? This will go quite a way towards helping to
develop some nice translucent effects.

Thanks all,
Jason

Not really information WPF tries to provide -- it's extremely expensive to
calculate for every possible element. For your specific scenario, I can
think of a couple approaches --
* After every change in layout, call InputHitTest with accordance of your
control and see if you get the same control
* or better, hook whatever logic put the control there in the first place.
E.g., override some method on Grid.

--
-Nick Kramer [MSFT]
http://blogs.msdn.com/nickkramer

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"Jason Dolinger" <jdolinger@lab49.com> wrote in message
news:euLXd1pJGHA.424@TK2MSFTNGP12.phx.gbl...
> Hi all,
>
> Is there a way to receive an event notification when some other element in
> a visual tree overlays the current element? For example, I have a grid
> with a TextBlock in it. At runtime another textblock gets inserted into
> the visual tree directly overlaying the existing box (or at least a
> portion of it). Is there some event that we can hook into when part of
> the tree is covered up?
>
> I'm trying to figure this out for translucency type issues. I want to
> adjust the Opacity value of this box when it is covered up. Even better,
> is there some way to indicate that when a particular visual element is in
> the tree, to change the opacity of the entire area underneath that
> element? This will go quite a way towards helping to develop some nice
> translucent effects.
>
> Thanks all,
> Jason