[UWP] connect the actual ObservableCollection to the ItemsSource

[StephaneDelcroix]

Description of Change

[UWP] connect the actual ObservableCollection to the ComboBox.ItemsSource as it looks like ComboBox doesn't correctly connect to INPC or INPP on a non-ObservableCollection<> ItemsSource. We'd have to look at the ComboBox source to be 100% sure...

The workaround is then to expose our collection as internal

Bugs Fixed

• https://bugzilla.xamarin.com/show_bug.cgi?id=51642

API Changes

Behavioral Changes

PR Checklist

• Has tests (if omitted, state reason in description)
• Rebased on top of master at time of PR
• Changes adhere to coding standard
• Consolidate commits as makes sense

[pauldipietro]

@StephaneDelcroix: On my end, it looks like that the changes break this on Android (both FormsActivity/AppCompat) and the items aren't showing up. iOS seems okay.

There's another issue I'm seeing too where if you add a label to the repro and have it set the text to whatever the SelectedItem is when SelectedIndexChanged fires, the first time something is selected, it's null. That appears to be occurring here because the event's getting invoked before the SelectedItem is updated; swapping their order appears to fix the issue (it also looks vaguely similar to 39407). If you want, I could make that change as another PR for history clarity, or you could include it in this one, since I'm assuming it's legitimate?

[StephaneDelcroix]

@pauldipietro push to this branch, it's fine

[pauldipietro]

I pushed that change which you can take a peek at, but Android still has issues with the items not showing up.

[TomQv]

When will this be merged?
Its desperatly awaited...

[pauldipietro]

I think this should be okay with [Preserve] having been added in for Android.