Ensuring your Xamarin application runs in a specific screen orientation couldn’t be simpler.
In your MainActivity class simply add the following to the [Activity()] Activity attribute.
ScreenOrientation.Portrait or ScreenOrientation.Landscape
So that the Activity Attribute looks something like this
[Activity(Label = "MyApp", Icon = "@mipmap/icon", Theme = "@style/MainTheme", ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation, ScreenOrientation = ScreenOrientation.Portrait)]
public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
{
// code here
}
Simple.