Visual Studio 16.10.0 breaks support for Xaml Islands Apps

[vsfeedback]

This issue has been moved from a ticket on Developer Community.

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[severity:I'm unable to use this version] [regression] [worked-in:16.9.8]
Visual Studio 16.10.0 and above (including 17) break support for Xaml islands apps throwing Error APPX0501 as seen below.
The issue has also been reported here and here, but no workaround has been found thus far.
This is a frequently reported bug breaking xaml islands support for a lot of developers.

APPX0501 Validation error. error 80080204: App manifest validation error: Line 66, Column 27, Reason: The field "[local-name()='Extensions']/[local-name()='Extension']/[local-name()='InProcessServer']/[local-name()='ActivatableClass']" with value "Microsoft.Toolkit.Win32.UI.XamlHost.XamlApplication" must only be declared once. A duplicate exists on Line 60, Column 27.

Severity Code Description Project File Line Suppression State
Error APPX0501 Validation error. error 80080204: App manifest validation error: Line 190, Column 27, Reason: The field "[local-name()='Extensions']/[local-name()='Extension']/[local-name()='InProcessServer']/[local-name()='ActivatableClass']" with value "Microsoft.Toolkit.Win32.UI.XamlHost.XamlApplication" must only be declared once. A duplicate exists on Line 80, Column 27. ModernFlyouts.Package C:\Users\samue\Source\Repos\ModernFlyouts-0.11final\ModernFlyouts.Package\bin\x64\Debug\AppxManifest.xml 1

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Original Comments

Feedback Bot on 1/11/2022, 07:44 PM:

We have directed your feedback to the appropriate engineering team for further evaluation. The team will review the feedback and notify you about the next steps.

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Original Solutions

(no solutions)

[atiyka]

Any estimation when will be this issue fixed?

[asklar]

@SvetBonev it looks like this got moved from devcom, but this is a regression in vs 16.10 (even when using old WinUI packages).
Can you help route this?

[atiyka]

Here is the issue about that app manifest validation error with the newest VS 2019 (also referenced in the post). I'm not sure where has to be posted/mentioned to be fixed this issue in VS.

[asklar]

@atiyka For VS to take a fix, it would need to be filed in the Developer Community website, here's the link to the original post: https://developercommunity2.visualstudio.com/t/Visual-Studio-16100-breaks-support-for/1634426?
Maybe there needs to be another issue filed in DevCom, since the original one was closed, hence why I asked Svet to help route it :)

[atiyka]

oh yeah, sorry, I didn't observed you not asking from me :)

[michael-hawker]

@StephenLPeters @asklar the VS issue is closed as a duplicate of this one (don't see a way to comment on it), and this one is closed as external. Something needs to be open somewhere no? Was originally reported here: CommunityToolkit/Microsoft.Toolkit.Win32#328

[asklar]

@srdjanjovcic I think this should be tracked in DevCom, agree? / is this something your team might be tracking already?

[srdjanjovcic]

@asklar I'll start email thread with relevant people from my team (it seems that I cannot ping them here?)