Addressed PR comments

native/Avalonia.Native/src/OSX/WindowImpl.mm

@@ -373,7 +373,9 @@ HRESULT WindowImpl::GetWindowZOrder(long* zOrder) {
             return E_POINTER;
         }
 
-        *zOrder = [Window orderedIndex];
+        // negate the value to match expected z-order in Avalonia
+        // (top-most window should have the highest z-order value)
+        *zOrder = -[Window orderedIndex];
         return S_OK;
     }
 }

samples/IntegrationTestApp/MacOSIntegration.cs

@@ -1,27 +0,0 @@
-using System;
-using System.Runtime.InteropServices;
-using Avalonia.Controls;
-
-namespace IntegrationTestApp
-{
-    public static class MacOSIntegration
-    {
-        [DllImport("/usr/lib/libobjc.dylib", EntryPoint = "sel_registerName")]
-        private static extern IntPtr GetHandle(string name);
-        
-        [DllImport("/usr/lib/libobjc.dylib", EntryPoint = "objc_msgSend")]
-        private static extern long Int64_objc_msgSend(IntPtr receiver, IntPtr selector);
-
-        private static readonly IntPtr s_orderedIndexSelector;
-
-        static MacOSIntegration()
-        {
-            s_orderedIndexSelector = GetHandle("orderedIndex");;
-        }
-        
-        public static long GetOrderedIndex(Window window)
-        {
-            return Int64_objc_msgSend(window.PlatformImpl!.Handle.Handle, s_orderedIndexSelector);
-        }
-    }
-}

samples/IntegrationTestApp/ShowWindowTest.axaml.cs

@@ -75,7 +75,7 @@ namespace IntegrationTestApp
 
         private void TimerOnTick(object? sender, EventArgs e)
         {
-            _orderTextBox!.Text = MacOSIntegration.GetOrderedIndex(this).ToString();
+            _orderTextBox!.Text = WindowZOrder.ToString();
         }
     }
 }

src/Avalonia.Native/WindowImpl.cs

@@ -103,14 +103,7 @@ namespace Avalonia.Native
 
         public Thickness OffScreenMargin { get; } = new Thickness();
 
-        public IntPtr? ZOrder
+        public IntPtr? ZOrder => _native.WindowZOrder;
-        {
-            get
-            {
-                // macOS returns z-order in reverse order - the topmost window has the lowest z-order
-                return new IntPtr(-_native.WindowZOrder.ToInt64());
-            }
-        }
 
         private bool _isExtended;
         public bool IsClientAreaExtendedToDecorations => _isExtended;

tests/Avalonia.IntegrationTests.Appium/WindowTests_MacOS.cs

@@ -52,7 +52,7 @@ namespace Avalonia.IntegrationTests.Appium
 
                 var secondaryWindowIndex = GetWindowOrder("SecondaryWindow");
 
-                Assert.Equal(1, secondaryWindowIndex);
+                Assert.Equal(-1, secondaryWindowIndex);
             }
         }
 
@@ -75,7 +75,7 @@ namespace Avalonia.IntegrationTests.Appium
                     .Release()
                     .Perform();
 
-                Assert.Equal(1, secondaryWindowIndex);
+                Assert.Equal(-1, secondaryWindowIndex);
             }
         }
 
@@ -94,7 +94,7 @@ namespace Avalonia.IntegrationTests.Appium
                 using (OpenWindow(new PixelSize(200, 100), ShowWindowMode.Modal, WindowStartupLocation.Manual))
                 {
                     var secondaryWindowIndex = GetWindowOrder("SecondaryWindow");
-                    Assert.Equal(1, secondaryWindowIndex);
+                    Assert.Equal(-1, secondaryWindowIndex);
                 }
             }
             finally
@@ -112,7 +112,7 @@ namespace Avalonia.IntegrationTests.Appium
             {
                 mainWindow.SendClick();
                 var secondaryWindowIndex = GetWindowOrder("SecondaryWindow");
-                Assert.Equal(1, secondaryWindowIndex);
+                Assert.Equal(-1, secondaryWindowIndex);
             }
         }
         
@@ -136,7 +136,7 @@ namespace Avalonia.IntegrationTests.Appium
             {
                 mainWindow.SendClick();
                 var secondaryWindowIndex = GetWindowOrder("SecondaryWindow");
-                Assert.Equal(1, secondaryWindowIndex);
+                Assert.Equal(-1, secondaryWindowIndex);
             }
 
             // Exit fullscreen by menu shortcut Command+R
@@ -159,7 +159,7 @@ namespace Avalonia.IntegrationTests.Appium
                 OpenWindow(null, ShowWindowMode.Modal, WindowStartupLocation.Manual).Dispose();
                 
                 var secondaryWindowIndex = GetWindowOrder("SecondaryWindow");
-                Assert.Equal(1, secondaryWindowIndex);
+                Assert.Equal(-1, secondaryWindowIndex);
             }
         }
 
@@ -212,7 +212,7 @@ namespace Avalonia.IntegrationTests.Appium
 
                 var secondaryWindowIndex = GetWindowOrder("SecondaryWindow");
 
-                Assert.Equal(2, secondaryWindowIndex);
+                Assert.Equal(-2, secondaryWindowIndex);
 
                 var sendToBack = _session.FindElementByAccessibilityId("SendToBack");
                 sendToBack.Click();
@@ -231,7 +231,7 @@ namespace Avalonia.IntegrationTests.Appium
         
                 var secondaryWindowIndex = GetWindowOrder("SecondaryWindow");
         
-                Assert.Equal(1, secondaryWindowIndex);
+                Assert.Equal(-1, secondaryWindowIndex);
             }
         }