[mac] fix build (#5608)

diff --git a/Xamarin.Forms.Platform.iOS/Forms.cs b/Xamarin.Forms.Platform.iOS/Forms.cs
index 5530f7a..13c0e50 100644 (file)
--- a/Xamarin.Forms.Platform.iOS/Forms.cs
+++ b/Xamarin.Forms.Platform.iOS/Forms.cs
@@ -98,8 +98,13 @@ namespace Xamarin.Forms
                        Device.SetIdiom(TargetIdiom.Desktop);
                        Device.SetFlowDirection(NSApplication.SharedApplication.UserInterfaceLayoutDirection.ToFlowDirection());
                        var mojave = new NSOperatingSystemVersion(10, 14, 0);
-                       if (NSProcessInfo.ProcessInfo.IsOperatingSystemAtLeastVersion(mojave))
-                               NSApplication.SharedApplication.Appearance = NSAppearance.GetAppearance(NSAppearance.NameAqua);
+                       if (NSProcessInfo.ProcessInfo.IsOperatingSystemAtLeastVersion(mojave) && 
+                               typeof(NSApplication).GetProperty("Appearance") is PropertyInfo appearance &&
+                               appearance != null)
+                       {
+                               var aquaAppearance = NSAppearance.GetAppearance(NSAppearance.NameAqua);
+                               appearance.SetValue(NSApplication.SharedApplication, aquaAppearance);
+                       }
 #endif
                        Device.SetFlags(s_flags);
                        Device.PlatformServices = new IOSPlatformServices();