foo.cs

using AppKit;
using CoreGraphics;
using Foundation;

namespace XamarinMacMojaveTest2
{
	[Register("AppDelegate")]
	public class AppDelegate : NSApplicationDelegate
	{
		MyViewTest outlineViewTest;
		public override void DidFinishLaunching(NSNotification notification)
		{
			outlineViewTest = new MyViewTest ();
		}
	}

	public class MyViewTest : NSObject
	{
		NSWindow Window;
		NSOutlineView Outline;
		public MyViewTest ()
		{
			NSWindowStyle windowStyle = NSWindowStyle.Closable | NSWindowStyle.Miniaturizable | NSWindowStyle.Resizable | NSWindowStyle.Titled;
			Window = new NSWindow (new CGRect (100, 100, 500, 500), windowStyle, NSBackingStore.Buffered, false);
			NSView outlineView = MakeView (Window.ContentView.Bounds);
			Window.ContentView.AddSubview (outlineView);
			Window.MakeKeyAndOrderFront (this);
		}

		NSView MakeView (CGRect frame)
		{
			Outline = new NSOutlineView (frame);
			NSScrollView scrollView = new NSScrollView (frame);
			scrollView.DocumentView = Outline;
			return scrollView;
		}
	}
}