perf(macOS): Avoid calling Subviews getter inside Dispose

Author: spouliot

src/SourceGenerators/Uno.UI.SourceGenerators/DependencyObject/DependencyObjectGenerator.cs

@@ -157,6 +157,9 @@ private void ProcessType(INamedTypeSymbol typeSymbol)
 					builder.AppendLineInvariant($"using Windows.UI.Xaml;");
 					builder.AppendLineInvariant($"using Windows.UI.Xaml.Data;");
 					builder.AppendLineInvariant($"using Uno.Diagnostics.Eventing;");
+					builder.AppendLineInvariant("#if __MACOS__");
+					builder.AppendLineInvariant("using AppKit;");
+					builder.AppendLineInvariant("#endif");
 
 					using (builder.BlockInvariant($"namespace {typeSymbol.ContainingNamespace}"))
 					{
@@ -667,21 +670,27 @@ protected sealed override void Dispose(bool disposing)
 							// a native representation via the IntPtr ctor, particularly on iOS.
 							__Store?.Dispose();
 
+#if __IOS__
 							var subviews = Subviews;
 
 							if (subviews.Length > 0)
 							{{
 								BinderCollector.RequestCollect();
-#if __IOS__
 								foreach (var v in subviews)
 								{{
 									v.RemoveFromSuperview();
 								}}
+							}}
 #elif __MACOS__
+							// avoids the managed array (and items) allocation(s) since we do not need them
+							if (this.GetSubviewsCount() > 0)
+							{{
+								BinderCollector.RequestCollect();
+
 								// avoids multiple native calls to remove subviews
-								Subviews = Array.Empty<AppKit.NSView>();
-#endif
+								Subviews = Array.Empty<NSView>();
 							}}
+#endif
 
 							base.Dispose(disposing);
 

src/Uno.UI/Extensions/UIViewExtensions.iOSmacOS.cs

@@ -4,14 +4,16 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Runtime.InteropServices;
 using System.Text;
 using Uno.UI.Extensions;
 using Windows.UI.Xaml;
 using Uno.Foundation.Logging;
 using Uno.UI.Controls;
-
-#if NET6_0_OR_GREATER
 using ObjCRuntime;
+
+#if !NET6_0_OR_GREATER
+using NativeHandle = System.IntPtr;
 #endif
 
 #if XAMARIN_IOS_UNIFIED
@@ -687,5 +689,30 @@ public static void SetNeedsDisplay(this _View view)
 			view.NeedsDisplay = true;
 #endif
 		}
+
+#if __MACOS__
+		static readonly NativeHandle selSubviewsHandle = Selector.GetHandle("subviews");
+#endif
+
+		[DllImport("/usr/lib/libobjc.dylib", EntryPoint="objc_msgSendSuper")]
+		private extern static NativeHandle NativeHandle_objc_msgSendSuper(NativeHandle receiver, IntPtr selector);
+
+		private static NativeHandle GetSubviewsHandle(this _View view)
+		{
+#if __IOS__
+			return NativeHandle_objc_msgSendSuper(view.SuperHandle, Selector.GetHandle("subviews"));
+#elif __MACOS__
+			return NativeHandle_objc_msgSendSuper(view.SuperHandle, selSubviewsHandle);
+#endif
+		}
+
+		[DllImport("/System/Library/Frameworks/CoreFoundation.framework/CoreFoundation")]
+		private extern static /* CFIndex */ nint CFArrayGetCount(/* CFArrayRef */ NativeHandle theArray);
+
+		internal static nint GetSubviewsCount(this _View view)
+		{
+			var handle = view.GetSubviewsHandle();
+			return CFArrayGetCount(handle);
+		}
 	}
 }