[Foundation] Improve nullability in NSArray.FromArray.

src/Foundation/NSArray.cs

@@ -675,6 +675,17 @@ static bool TryGetItem<T> (NativeHandle elementHandle, Converter<NativeHandle, T
 			return ArrayFromHandle<T> (handle, createObject, NSNullBehavior.Drop, releaseHandle)!;
 		}
 
+		/// <summary>Returns a strongly-typed C# array from a handle to an NSArray, dropping null elements.</summary>
+		/// <typeparam name="T">Parameter type, determines the kind of array returned.</typeparam>
+		/// <param name="handle">Pointer (handle) to the unmanaged object.</param>
+		/// <param name="nsNullElementBehavior">How to handle null and NSNull elements in the native array.</param>
+		/// <param name="releaseHandle">Whether the native NSArray instance should be released before returning or not.</param>
+		/// <returns>A C# array with the values (excluding null elements). Returns <see langword="null" /> if the handle is <see cref="NativeHandle.Zero" />.</returns>
+		internal static T []? ArrayFromHandleDropNullElements<T> (NativeHandle handle, NSNullBehavior nsNullElementBehavior, bool releaseHandle = false) where T : class, INativeObject
+		{
+			return ArrayFromHandle<T> (handle, (h) => Runtime.GetINativeObject<T> (h, false)!, nsNullElementBehavior, releaseHandle)!;
+		}
+
 		/// <summary>Returns a strongly-typed C# array from a handle to an NSArray, dropping null elements and guaranteeing a non-null return value.</summary>
 		/// <typeparam name="T">Parameter type, determines the kind of array returned.</typeparam>
 		/// <param name="handle">Pointer (handle) to the unmanaged object.</param>
@@ -751,38 +762,51 @@ internal static T [] NonNullEnumsFromHandle<T> (NativeHandle handle) where T : S
 				(element) => (T) Enum.ToObject (typeof (T), Runtime.GetNSObject<NSNumber> (element)?.LongValue ?? 0));
 		}
 
-#nullable disable
-		/// <typeparam name="T">Parameter type, determines the kind of
-		/// 	array returned, limited to NSObject and subclasses of it.</typeparam>
-		///         <param name="weakArray">Handle to an weakly typed NSArray.</param>
-		///         <summary>Returns a strongly-typed C# array of the parametrized type from a weakly typed NSArray.</summary>
-		///         <returns>An C# array with the values.</returns>
-		///         <remarks>
-		///           <para>Use this method to get a set of NSObject arrays from an NSArray.</para>
-		///           <example>
-		///             <code lang="c#"><![CDATA[
+		/// <summary>Creates a strongly-typed C# array from a weakly typed <see cref="NSArray" />.</summary>
+		/// <typeparam name="T">The element type for the returned array, limited to <see cref="NSObject" /> and subclasses.</typeparam>
+		/// <param name="weakArray">A weakly typed <see cref="NSArray" /> to convert, or <see langword="null" />.</param>
+		/// <returns>
+		///   A C# array of <typeparamref name="T" /> elements, or <see langword="null" /> if
+		///   <paramref name="weakArray" /> is <see langword="null" /> or a conversion error occurs.
+		///   Elements that are <see cref="NSNull" /> or not compatible with <typeparamref name="T" /> are excluded.
+		/// </returns>
+		/// <remarks>
+		///   <example>
+		///     <code lang="c#"><![CDATA[
 		/// NSArray someArray = ...;
 		///
-		/// NSString [] values = NSArray.FromArray<CGImage> (someArray);
+		/// var values = NSArray.FromArray<NSString> (someArray);
 		/// ]]></code>
-		///           </example>
-		///         </remarks>
-		static public T [] FromArray<T> (NSArray weakArray) where T : NSObject
+		///   </example>
+		/// </remarks>
+		public static T []? FromArray<T> (NSArray? weakArray) where T : NSObject
 		{
-			if (weakArray is null || weakArray.Handle == NativeHandle.Zero)
-				return null;
 			try {
-				nuint n = weakArray.Count;
-				T [] ret = new T [n];
-				for (nuint i = 0; i < n; i++) {
-					ret [i] = Runtime.GetNSObject<T> (weakArray.ValueAt (i));
-				}
-				return ret;
+				var rv = ArrayFromHandleDropNullElements<T> (weakArray.GetHandle (), NSNullBehavior.DropIfIncompatible);
+				GC.KeepAlive (weakArray);
+				return rv;
 			} catch {
 				return null;
 			}
 		}
 
+		/// <summary>
+		///   Creates a strongly-typed C# array from a weakly typed <see cref="NSArray" />,
+		///   dropping null and <see cref="NSNull" /> elements and guaranteeing a non-null return value.
+		/// </summary>
+		/// <typeparam name="T">The element type for the returned array, limited to <see cref="NSObject" /> and subclasses.</typeparam>
+		/// <param name="weakArray">A weakly typed <see cref="NSArray" /> to convert, or <see langword="null" />.</param>
+		/// <returns>
+		///   A C# array of <typeparamref name="T" /> elements (excluding null and <see cref="NSNull" /> elements).
+		///   Returns an empty array if <paramref name="weakArray" /> is <see langword="null" /> or empty.
+		/// </returns>
+		internal static T [] ToNonNullArrayDropNullElements<T> (NSArray? weakArray) where T : NSObject
+		{
+			var rv = NSArray.NonNullArrayFromHandleDropNullElements<T> (weakArray.GetHandle ());
+			GC.KeepAlive (weakArray);
+			return rv;
+		}
+#nullable disable
 		/// <typeparam name="T">Parameter type, determines the kind of
 		/// 	array returned, can be either an NSObject, or other
 		/// 	CoreGraphics data types.</typeparam>

src/MetalKit/MTKMesh.cs

@@ -16,7 +16,7 @@ public partial class MTKMesh {
 		///         <summary>Creates and returns a new Metal Kit mesh from the supplied Model IO asset.</summary>
 		///         <returns>To be added.</returns>
 		///         <remarks>To be added.</remarks>
-		public static MTKMesh []? FromAsset (MDLAsset asset, IMTLDevice device, out MDLMesh [] sourceMeshes, out NSError error)
+		public static MTKMesh []? FromAsset (MDLAsset asset, IMTLDevice device, out MDLMesh []? sourceMeshes, out NSError error)
 		{
 			NSArray aret;
 

src/UIKit/UIFontDescriptor.cs

@@ -532,9 +532,7 @@ public NSCharacterSet? CharacterSet {
 		public UIFontDescriptor [] CascadeList {
 			get {
 				var o = GetObject (UIFontDescriptor.CascadeListAttribute) as NSArray;
-				if (o is null)
-					return new UIFontDescriptor [0];
-				return NSArray.FromArray<UIFontDescriptor> (o);
+				return NSArray.ToNonNullArrayDropNullElements<UIFontDescriptor> (o);
 			}
 		}
 

src/bgen/Generator.cs

@@ -4068,7 +4068,7 @@ void GenerateProperty (Type type, PropertyInfo pi, List<string> instance_fields_
 					print ("return src is null ? null! : new {0}(src);", TypeManager.FormatType (pi.DeclaringType, pi.PropertyType));
 				} else {
 					if (TypeManager.IsArrayOfWrappedType (pi.PropertyType))
-						print ("return NSArray.FromArray<{0}>({1} as NSArray);", TypeManager.FormatType (pi.DeclaringType, pi.PropertyType.GetElementType ()), wrap);
+						print ("return NSArray.FromArray<{0}>({1} as NSArray){2};", TypeManager.FormatType (pi.DeclaringType, pi.PropertyType.GetElementType ()), wrap, nullable ? "" : "!");
 					else if (pi.PropertyType.IsValueType)
 						print ("return ({0}) ({1});", TypeManager.FormatType (pi.DeclaringType, pi.PropertyType), wrap);
 					else

tests/monotouch-test/Metal/MTKMeshTest.cs

@@ -0,0 +1,43 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using System;
+using System.Numerics;
+
+using Foundation;
+using Metal;
+using MetalKit;
+using ModelIO;
+
+using NUnit.Framework;
+
+using Vector3i = global::CoreGraphics.NVector3i;
+
+namespace MonoTouchFixtures.MetalKit {
+
+	[TestFixture]
+	[Preserve (AllMembers = true)]
+	public class MTKMeshTest {
+
+		[Test]
+		public void FromAsset ()
+		{
+			var device = MTLDevice.SystemDefault;
+			if (device is null)
+				Assert.Inconclusive ("Metal is not supported on this device.");
+
+			using var allocator = new MTKMeshBufferAllocator (device);
+			using var mesh = MDLMesh.CreateBox (new Vector3 (1, 1, 1), new Vector3i (1, 1, 1), MDLGeometryType.Triangles, false, allocator);
+			using var asset = new MDLAsset ();
+			asset.AddObject (mesh);
+
+			var result = MTKMesh.FromAsset (asset, device, out var sourceMeshes, out var error);
+
+			Assert.IsNull (error, "error");
+			Assert.IsNotNull (result, "result");
+			Assert.That (result!.Length, Is.GreaterThan (0), "result length");
+			Assert.IsNotNull (sourceMeshes, "sourceMeshes");
+			Assert.AreEqual (result.Length, sourceMeshes!.Length, "sourceMeshes length");
+		}
+	}
+}

tests/monotouch-test/ObjCRuntime/RegistrarTest.cs

@@ -5720,13 +5720,13 @@ public void DecidePolicy (WKWebView webView, WKNavigationAction navigationAction
 
 	// These classes implement Metal* protocols, so that the generated registrar code includes the corresponding Metal* headers.
 	// https://github.com/dotnet/macios/issues/4422
-	class MetalKitTypesInTheSimulator : NSObject, MetalKit.IMTKViewDelegate {
-		public void Draw (MetalKit.MTKView view)
+	class MetalKitTypesInTheSimulator : NSObject, global::MetalKit.IMTKViewDelegate {
+		public void Draw (global::MetalKit.MTKView view)
 		{
 			throw new NotImplementedException ();
 		}
 
-		public void DrawableSizeWillChange (MetalKit.MTKView view, CGSize size)
+		public void DrawableSizeWillChange (global::MetalKit.MTKView view, CGSize size)
 		{
 			throw new NotImplementedException ();
 		}