Xamarin forms WPF

Using sharpgl with vs2017 (xamarin forms & WPF) for a customrender like this

public sealed class VDSPreviewWpfSharpGL : OpenGLControl

i get this erro on runtime
System.Exception: 'Per il componente 'SapAndroidApp.Wpf.VDSPreviewWpfSharpGL' non è disponibile una risorsa identificata dall'URI '/SharpGL.WPF;component/openglcontrol.xaml'.'
hresult: -2146233088

something like
For the component 'SapAndroidApp.Wpf.VDSPreviewWpfSharpGL' a resource identified by the URI '/SharpGL.WPF ;component/openglcontrol.xaml' is not available