RenderTargetBitmap.LoadAsync fails with UIElement on a Flyout? (value out of range)

Question

I have a Rectangle that contains a thumbnail that I render to a bitmap using RenderTargetBitmap.  When the Rectangle was a child of the main page grid this worked fine.  But now that it is a child control in a Flyout I get a "Value does not fall within the expected range" Exception from mscorlib.dll.  

As a test I created a Rectangle directly on the main page grid that had the same Fill source as the (now) Flyout based Rectangle.  I passed it to RenderTargetBitmap.LoadAsync() instead and it worked fine.  As an additional test, I set it's opacity to 0%.  This time the whole IDE crashed.

Can I fix this without having to resort to a duplicate Rectangle on the main page?

UPDATE: For now I am moving the duplicate rectangle far off the client area with the following statement:

            rectDuplicateThumbnail.Margin = new Thickness(-1000, -1000, -1000 + rectVideomarkThumbnail.ActualWidth, -1000 + rectVideomarkThumbnail.ActualHeight);

I'd still like to get rid of this kludge if possible.

-- roschler

Answer 1

This is by design and documented in the class:

http://msdn.microsoft.com/en-us/library/windows/apps/windows.ui.xaml.media.imaging.rendertargetbitmap.aspx

See the notes:

Content that's not directly connected to the XAML visual tree and the content of the main window won't be captured. This includes Popup content, which is considered to be like a sub-window.

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Jeff Sanders (MSFT)

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Answer 2

Ok, thanks. I'll just keep using a hidden Rectangle then.  At least it works.

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-- roschler