Incorrect target type for RelativeAncestor attached properties

[Sergio0694]

Describe the bug

The attached properties for the "relative ancestor" feature are currently targeting the wrong type:

https://github.com/CommunityToolkit/WindowsCommunityToolkit/blob/44ad0cc6806c99f1a693c923cb94ea7551718c13/Microsoft.Toolkit.Uwp.UI/Extensions/FrameworkElement/FrameworkElementExtensions.RelativeAncestor.cs#L18-L21

These are defined in FrameworkElementExtensions but target a DependencyObject. This is not correct on its own, but in particular it also makes the APIs technically more error prone, as there is no type guarantee at build-time, and we're doing additional checks at runtime to ensure the input elements are in fact FrameworkElement-s, otherwise we do nothing:

https://github.com/CommunityToolkit/WindowsCommunityToolkit/blob/44ad0cc6806c99f1a693c923cb94ea7551718c13/Microsoft.Toolkit.Uwp.UI/Extensions/FrameworkElement/FrameworkElementExtensions.RelativeAncestor.cs#L62-L65

Given that these APIs only make sense for FrameworkElement instances, and that they're defined within FrameworkElementExtensions too, we should update the signature and have them only target FrameworkElement objects. I should note: this would not be a source breaking change when the API was being used correctly, but it would be a binary breaking change.

[oscarjaergren]

Does this cause relativeAncestor not to work?

"DataContext="{Binding DataContext.(mainDetails:MasterDetailViewModel.CasaDetailsViewModel), RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type mainDetails:MasterDetailView}}}""
and this version without being qualifed

DataContext="{Binding DataContext.CasaDetailsViewModel, RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type mainDetails:MasterDetailView}}}"

Previously worked, but when I tried upgrading to source generator it no longer worked, as it just couldn't find the viewmodel, no error messages or anything, just a crash whenever I opened it due to property being null

[michael-hawker]

@oscarjaergren your example appears to be WPF based, this issue is about the UWP polyfill we have for RelativeSource Mode=FindAncestor in the Windows Community Toolkit and is unrelated to whatever issue you may have had.

If there's some difference between code you had before with the MVVM Toolkit and code after switching to the Source Generator version, you should open a discussion/issue in the .NET Community Toolkit repo here: https://aka.ms/toolkit/dotnet

[michael-hawker]

Thanks @Sergio0694, brought this over to the new repo and will fix in #105.

Note, Ancestor can be a DependencyObject still as it's the output of the call to FindAscendant which can return a DependencyObject.

However, you're correct, since we generally want to wait until the element is loaded, we should make AncestorType dependent on FrameworkElement. Related to our discussion in Labs too: CommunityToolkit/Labs-Windows#449

Though technically, we could still call the visual tree helpers on a DependencyObject, I don't think there's going to be many of those cases though, so think fine to exclude?