Sample App: OnXamlRendered does not get called.

[Rosuavio]

Describe the bug

In the sample app, for samples with *.xmal.cs files, if the page inherits from IXamlRenderListener OnXamlRendered does not seem to be getting called.
My investigating showed that in this line the cast fails for the pages I tested (CarouselPage, DockPanel, AdaptiveGridView)
https://github.com/windows-toolkit/WindowsCommunityToolkit/blob/205eedfc930e62dd8e21c8a8df63a9e75ba4955f/Microsoft.Toolkit.Uwp.SampleApp/Pages/SampleController.xaml.cs#L555

• Is this bug a regression in the toolkit? If so, what toolkit version did you last see it work: cb4dc66
  It was introduced in Type property is now optional for Samples #3648

Steps to Reproduce

• Can this be reproduced in the Sample App? (Either in a sample as-is or with new XAML pasted in the editor.) If so, please provide custom XAML or steps to reproduce. If not, let us know why it can't be reproduced (e.g. more complex setup, environment, dependencies, etc...)

Steps to reproduce the behavior:

1. Given the Sample App is open
2. Open a sample that makes use of the functionality (like "Carousel" )
3. Notice that the action it was supposed to take once it loaded (load carousel items for the Carousel) does not occur.

Expected behavior

For every sample that uses IXamlRenderListener and OnXamlRendered the code in OnXamlRendered is called when the sample is loaded.

Screenshots

If applicable, add screenshots to help explain your problem.

Environment

NuGet Package(s): 

Package Version(s): 

Windows 10 Build Number:
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [ ] May 2019 Update (18362)
- [ ] May 2020 Update (19041)
- [x] ???? ????? Update (19042)
- [ ] Insider Build (build number: )

App min and target version:
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [ ] May 2019 Update (18362)
- [ ] May 2020 Update (19041)
- [ ] Insider Build (xxxxx)

Device form factor:
- [x] Desktop
- [ ] Xbox
- [ ] Surface Hub
- [ ] IoT

Visual Studio 
- [ ] 2017 (version: )
- [x] 2019 (version: ) 
- [ ] 2019 Preview (version: )

Additional context

Add any other context about the problem here.

[ghost]

Hello RosarioPulella, thank you for opening an issue with us!

I have automatically added a "needs triage" label to help get things started. Our team will analyze and investigate the issue, and escalate it to the relevant team if possible. Other community members may also look into the issue and provide feedback 🙌

[michael-hawker]

I wasn't able to reproduce for AdaptiveGridView (which is parsing twice), but was able to see it for Carousel, so investigating...

[michael-hawker]

Think I see the problem, assumed I'd find a XamlRoot and made wrong assumption about what to do if I didn't. Will compare against previous behavior and update.

Did also see where we update twice. We load once from the Pivot SelectionChanged and also in the SamplePage_Loaded method, but we have a comment there about not getting the event from the Pivot selection changed, so wonder if this was an OS bug which was later fixed... We could add a private value to track if we've rendered from loading the initial sample yet to only render once, but not sure if we want to mess with that now or just fix later when we work on samples in 7.1...

[michael-hawker]

Alright, testing out a fix. Tried to clean-up the notion we had of the SampleContent vs SamplePage too.