GetApperanceWhenContainedIn method from the UIAppearance API is deprecated in iOS9 (confirmed on the Xamarin page at https://developer.xamarin.com/guides/ios/user_interface/introduction_to_the_appearance_api).
Apple state that [UIAppearance appearanceWhenContainedInInstancesOfClasses] should be used instead but this is not currently supported in Xamarin.iOS and I cannot find any reference to it being addressed.
What's the use case ?
The old API is used internally in our UIAppearance managed API. Since we support iOS6+ we won't* be switching the API we use (and break existing code on older OS).
* the new API is available (internally) when using tvOS (since it's available in all supported versions).