Make static and add using

MvvmCross.Plugins/Share/Platform/iOS/MvxShareTask.cs

@@ -11,6 +11,7 @@ using MvvmCross.Platform.iOS.Platform;
 using MvvmCross.Platform.iOS.Views;
 using MvvmCross.iOS.Support.Views;
 using Twitter;
+using UIKit;
 
 namespace MvvmCross.Plugins.Share.iOS
 {

MvvmCross/Platform/iOS/Views/Extensions.cs

@@ -177,7 +177,7 @@ namespace MvvmCross.iOS.Support.Views
 			return descendantViews;
 		}
 
-        public virtual UIViewController GetTopModalHostViewController(this UIWindow window)
+        public static UIViewController GetTopModalHostViewController(this UIWindow window)
         {
             var vc = window.RootViewController;
             do {
@@ -189,4 +189,4 @@ namespace MvvmCross.iOS.Support.Views
             return vc;
         }
     }
-}
+}