[mac] Manual theme image handling

Author: Eric Maupin

Xamarin.PropertyEditing.Mac.Standalone/ViewController.cs

@@ -93,7 +93,9 @@ partial void OnThemeChanged (NSObject sender)
 					appearance = NSAppearance.NameVibrantDark;
 			}
 
-			View.Appearance = NSAppearance.GetAppearance (appearance);
+			var realAppearance = NSAppearance.GetAppearance (appearance);
+			((HostResourceProvider)PropertyPanel.HostResourceProvider).CurrentAppearance = realAppearance;
+			View.Appearance = realAppearance;
 		}
 	}
 }

Xamarin.PropertyEditing.Mac/HostResourceProvider.cs

@@ -7,6 +7,12 @@ namespace Xamarin.PropertyEditing.Mac
 	public class HostResourceProvider
 		: IHostResourceProvider
 	{
+		public NSAppearance CurrentAppearance
+		{
+			get;
+			set;
+		}
+
 		public virtual NSAppearance GetVibrantAppearance (NSAppearance appearance)
 		{
 			if (appearance == null)
@@ -25,6 +31,9 @@ public virtual NSColor GetNamedColor (string name)
 
 		public virtual NSImage GetNamedImage (string name)
 		{
+			if ((CurrentAppearance ?? NSAppearance.CurrentAppearance).Name.ToLower ().Contains ("dark"))
+				name += "~dark";
+
 			return NSImage.ImageNamed (name);
 		}