In my Xamarin solution, I added a new library project in a Controls solution folder. From my XAML in Views I called my component and everything was working fine.
I don't know if something changed today after the update to iOS 10 and Visual Studio for Mac but not if I try to compile my solution, I receive an error
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> Xamarin.Forms.Xaml.XamlParseException: Position 43:38. Type Doughnut not found in xmlns clr-namespace:Mobile.Controls.Wheel;assembly=Mobile.Controls.Wheel
at Xamarin.Forms.Xaml.Internals.XamlTypeResolver.Xamarin.Forms.Xaml.IXamlTypeResolver.Resolve (System.String qualifiedTypeName, System.IServiceProvider serviceProvider)
The XAML page is so defined:
<ContentPage [...]
xmlns:ctl="clr-namespace:Mobile.Controls.Wheel;assembly=Mobile.Controls.Wheel"
x:Class="Views.DashboardPage">
<StackLayout>
<ctl:Doughnut HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand" />
</StackLayout>
</ContentPage>
Doughnut is a class derived from ContentView in Mobile.Controls.Wheel.