[Foundation] Improve NSArray.FromIntPtrs slightly. (#24501)

* Enable nullability.
* Simplify code, with both reduced memory footprint, and faster execution speed.
* Add tests.
* Add xml docs.

Contributes towards #17285.

Author: rolfbjarne

src/Foundation/NSArray.cs

@@ -283,6 +283,7 @@ static public NSArray FromStrings (IReadOnlyList<string> items)
 			}
 		}
 
+#nullable enable
 		/// <summary>Create an <see cref="NSArray" /> from the specified pointers.</summary>
 		/// <param name="items">Array of pointers (to <see cref="NSObject" /> instances).</param>
 		/// <remarks>If the <paramref name="items" /> array is null, an <see cref="ArgumentNullException" /> is thrown.</remarks>
@@ -293,24 +294,25 @@ static internal NSArray FromIntPtrs (IntPtr [] items)
 
 			unsafe {
 				fixed (IntPtr* valuesPtr = items)
-					return Runtime.GetNSObject<NSArray> (NSArray.FromObjects ((IntPtr) valuesPtr, items.Length))!;
+					return Runtime.GetNSObject<NSArray> (NSArray.FromObjects ((IntPtr) valuesPtr, items.Length)) ?? new NSArray ();
 			}
 		}
 
-		static public NSArray FromIntPtrs (NativeHandle [] vals)
+		/// <summary>Create an <see cref="NSArray" /> from the specified pointers.</summary>
+		/// <param name="vals">Array of pointers (to <see cref="NSObject" /> instances).</param>
+		/// <remarks>If the <paramref name="vals" /> array is null, an <see cref="ArgumentNullException" /> is thrown.</remarks>
+		public static NSArray FromIntPtrs (NativeHandle [] vals)
 		{
 			if (vals is null)
-				throw new ArgumentNullException ("vals");
-			int n = vals.Length;
-			IntPtr buf = Marshal.AllocHGlobal (n * IntPtr.Size);
-			for (int i = 0; i < n; i++)
-				Marshal.WriteIntPtr (buf, i * IntPtr.Size, vals [i]);
-
-			NSArray arr = Runtime.GetNSObject<NSArray> (NSArray.FromObjects (buf, vals.Length));
+				throw new ArgumentNullException (nameof (vals));
 
-			Marshal.FreeHGlobal (buf);
-			return arr;
+			unsafe {
+				fixed (NativeHandle* valuesPtr = vals) {
+					return Runtime.GetNSObject<NSArray> (NSArray.FromObjects ((IntPtr) valuesPtr, vals.Length)) ?? new NSArray ();
+				}
+			}
 		}
+#nullable disable
 
 		internal static nuint GetCount (IntPtr handle)
 		{

tests/cecil-tests/Documentation.KnownFailures.txt

@@ -11806,7 +11806,6 @@ M:Foundation.INSUrlSessionWebSocketDelegate.DidOpen(Foundation.NSUrlSession,Foun
 M:Foundation.INSXpcListenerDelegate.ShouldAcceptConnection(Foundation.NSXpcListener,Foundation.NSXpcConnection)
 M:Foundation.NSArray.ArrayFromHandle``1(ObjCRuntime.NativeHandle,System.Converter{ObjCRuntime.NativeHandle,``0},System.Boolean)
 M:Foundation.NSArray.EnumsFromHandle``1(ObjCRuntime.NativeHandle)
-M:Foundation.NSArray.FromIntPtrs(ObjCRuntime.NativeHandle[])
 M:Foundation.NSArray.FromNSObjects``1(``0[][])
 M:Foundation.NSArray.FromNSObjects``1(``0[0:,0:])
 M:Foundation.NSArray.FromStrings(System.Collections.Generic.IReadOnlyList{System.String})

tests/monotouch-test/Foundation/NSArray1Test.cs

@@ -125,6 +125,38 @@ public void ToArray_T ()
 			}
 		}
 
+		[Test]
+		public void FromIntPtrs_NativeHandle ()
+		{
+			var str1 = (NSString) "1";
+			var str2 = (NSString) "2";
+			var str3 = (NSString) "3";
+
+			var handles = new NativeHandle [] { str1.Handle, str2.Handle, str3.Handle };
+			using (var arr = NSArray.FromIntPtrs (handles)) {
+				Assert.AreEqual ((nuint) 3, arr.Count, "NSArray Count");
+				Assert.AreEqual ("1", arr.GetItem<NSString> (0).ToString (), "NSArray item 0");
+				Assert.AreEqual ("2", arr.GetItem<NSString> (1).ToString (), "NSArray item 1");
+				Assert.AreEqual ("3", arr.GetItem<NSString> (2).ToString (), "NSArray item 2");
+			}
+		}
+
+		[Test]
+		public void FromIntPtrs_NativeHandle_Null ()
+		{
+			NativeHandle []? handles = null;
+			Assert.Throws<ArgumentNullException> (() => NSArray.FromIntPtrs (handles!), "Null array");
+		}
+
+		[Test]
+		public void FromIntPtrs_NativeHandle_Empty ()
+		{
+			var handles = new NativeHandle [0];
+			using (var arr = NSArray.FromIntPtrs (handles)) {
+				Assert.AreEqual ((nuint) 0, arr.Count, "NSArray Count");
+			}
+		}
+
 #if false // https://github.com/dotnet/macios/issues/15577
 		[Test]
 		public void GetDifferenceFromArrayTest ()