Fix CollectionView Header is not visible when ItemsSource is not set and an EmptyView is set in iOS, Mac platform

src/Controls/src/Core/Handlers/Items2/iOS/StructuredItemsViewController2.cs

@@ -48,6 +48,26 @@ protected override void Dispose(bool disposing)
 
 		protected override bool IsHorizontal => (ItemsView?.ItemsLayout as ItemsLayout)?.Orientation == ItemsLayoutOrientation.Horizontal;
 
+		public override nint NumberOfSections(UICollectionView collectionView)
+		{
+			var count = base.NumberOfSections(collectionView);
+
+			// UICollectionViewCompositionalLayout does not render global boundary supplementary items
+			// (header/footer set on NSCollectionLayoutConfiguration) when there are 0 sections.
+			// Return at least 1 section so the header/footer remains visible when ItemsSource is empty.
+			// Only applies to non-grouped collections: grouped collections put group headers in
+			// per-section supplementary items, which would crash when accessing the empty group source.
+			if (count == 0
+				&& ItemsSource is not null && !(ItemsView is GroupableItemsView { IsGrouped: true })
+				&& (ItemsView?.Header is not null || ItemsView?.HeaderTemplate is not null
+					|| ItemsView?.Footer is not null || ItemsView?.FooterTemplate is not null))
+			{
+				return 1;
+			}
+
+			return count;
+		}
+
 		internal void UpdateHeaderView()
 		{
 			// Clean up header view if no header content

src/Controls/src/Core/PublicAPI/net-ios/PublicAPI.Unshipped.txt

@@ -4,5 +4,6 @@ override Microsoft.Maui.Controls.Shapes.Shape.OnPropertyChanged(string? property
 override Microsoft.Maui.Controls.Platform.Compatibility.ShellTableViewController.LoadView() -> void
 *REMOVED*~override Microsoft.Maui.Controls.Platform.Compatibility.ShellSectionRootRenderer.TraitCollectionDidChange(UIKit.UITraitCollection previousTraitCollection) -> void
 ~override Microsoft.Maui.Controls.Handlers.Items2.CollectionViewHandler2.DisconnectHandler(UIKit.UIView platformView) -> void
+~override Microsoft.Maui.Controls.Handlers.Items2.StructuredItemsViewController2<TItemsView>.NumberOfSections(UIKit.UICollectionView collectionView) -> nint
 override Microsoft.Maui.Controls.Platform.Compatibility.ShellItemRenderer.ViewDidAppear(bool animated) -> void
 ~override Microsoft.Maui.Controls.Platform.Compatibility.ShellSectionRenderer.DidMoveToParentViewController(UIKit.UIViewController parent) -> void

src/Controls/src/Core/PublicAPI/net-maccatalyst/PublicAPI.Unshipped.txt

@@ -4,5 +4,6 @@ override Microsoft.Maui.Controls.Shapes.Shape.OnPropertyChanged(string? property
 override Microsoft.Maui.Controls.Platform.Compatibility.ShellTableViewController.LoadView() -> void
 *REMOVED*~override Microsoft.Maui.Controls.Platform.Compatibility.ShellSectionRootRenderer.TraitCollectionDidChange(UIKit.UITraitCollection previousTraitCollection) -> void
 ~override Microsoft.Maui.Controls.Handlers.Items2.CollectionViewHandler2.DisconnectHandler(UIKit.UIView platformView) -> void
+~override Microsoft.Maui.Controls.Handlers.Items2.StructuredItemsViewController2<TItemsView>.NumberOfSections(UIKit.UICollectionView collectionView) -> nint
 override Microsoft.Maui.Controls.Platform.Compatibility.ShellItemRenderer.ViewDidAppear(bool animated) -> void
 ~override Microsoft.Maui.Controls.Platform.Compatibility.ShellSectionRenderer.DidMoveToParentViewController(UIKit.UIViewController parent) -> void

src/Controls/tests/TestCases.HostApp/Issues/Issue34897.cs

@@ -0,0 +1,54 @@
+using Microsoft.Maui.Controls;
+using System.Collections.ObjectModel;
+
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 34897, "CollectionView Header is not visible when ItemsSource is not set and EmptyView is set", PlatformAffected.iOS | PlatformAffected.macOS)]
+public class Issue34897 : ContentPage
+{
+	public Issue34897()
+	{
+		var collectionView = new CollectionView
+		{
+			ItemsLayout = new GridItemsLayout(2, ItemsLayoutOrientation.Vertical),
+			AutomationId = "Issue34897CollectionView",
+			Header = new Label
+			{
+				Text = "CollectionView Header",
+				AutomationId = "Issue34897Header",
+				BackgroundColor = Colors.LightBlue,
+			},
+			EmptyView = new Label
+			{
+				Text = "No items available",
+				AutomationId = "Issue34897EmptyView",
+				BackgroundColor = Colors.LightYellow,
+			},
+			Footer = new Label
+			{
+				Text = "CollectionView Footer",
+				AutomationId = "Issue34897Footer",
+				BackgroundColor = Colors.LightGreen,
+			},
+		};
+
+		var grid = new Grid
+		{
+			RowDefinitions =
+			{
+				new RowDefinition(GridLength.Auto),
+				new RowDefinition(GridLength.Star),
+			}
+		};
+
+		var label = new Label
+		{
+			Text = "Header, Footer and EmptyView should all be visible below:",
+		};
+
+		grid.Add(label, 0, 0);
+		grid.Add(collectionView, 0, 1);
+
+		Content = grid;
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue34897.cs

@@ -0,0 +1,23 @@
+#if TEST_FAILS_ON_WINDOWS // This test fails on Windows because we no longer works with CollectionView on Windows.
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue34897 : _IssuesUITest
+{
+	public Issue34897(TestDevice device) : base(device) { }
+
+	public override string Issue => "CollectionView Header is not visible when ItemsSource is not set and EmptyView is set";
+
+	[Test]
+	[Category(UITestCategories.CollectionView)]
+	public void CollectionViewHeaderVisibleWithEmptyViewAndNullItemsSource()
+	{
+		App.WaitForElement("Issue34897EmptyView");
+		App.WaitForElement("Issue34897Header");
+		App.WaitForElement("Issue34897Footer");
+	}
+}
+#endif