Today I learned how to write a custom renderer in iOS for a ContentPage in Xamarin Forms.
At first I tried using extending Xamarin Forms' View class, but I found that the View did not size itself properly within the content page which was hosted in a NavigationPage. My custom content, which was supposed to be in the vertical center, appeared too far down because it didn't know it was being pushed down by the navigation bar.
-> Content View
-> Custom View
-> Custom Content View
and everything is centered properly.