title: Xamarin.Forms class in namespace not found (only on iOS)
body: <p>I've a Xamarin.Forms solutions, which consists of several PCLs and device-specific projects:</p>
  
  <ul>
  <li>MyApp.Controls (Portable)
  
  <ul>
  <li>Helper (MyApp.Controls.Helper)</li>
  </ul></li>
  <li>MyApp.App (Portable)</li>
  <li>MyApp.iOS</li>
  <li>MyApp.Android</li>
  </ul>
  
  <p>MyApp.App is my main implementation, where the App.xaml and all Views/ ViewModels are implemented. This project references MyApp.Controls and refers to this project within XAML via xmlns. The XAML-references work fine on Android but on iOS I get the following exception:
  controls:MyClass not found in xmlns clr-namespace:MyApp.Controls.Helper;assembly=MyApp.Controls</p>
  
  <p>I have no idea, why "MyClass" can't be resolved on iOS. I'm using Xamarin.Forms 2.3.3.180.</p>