Include headers/footers in EmptySource count so they show up when ItemsSource is null (#15979)

* Include headers/footers in EmptySource count so they show up when ItemsSource is null
Fixes #8934

* More tests

src/Controls/src/Core/Handlers/Items/Android/Adapters/EmptyViewAdapter.cs

@@ -10,12 +10,12 @@ namespace Microsoft.Maui.Controls.Handlers.Items
 {
 	public class EmptyViewAdapter : RecyclerView.Adapter
 	{
-		int _headerHeight;
+		double _headerHeight;
 		int _headerViewType;
 		object _headerView;
 		DataTemplate _headerViewTemplate;
 
-		int _footerHeight;
+		double _footerHeight;
 		int _footerViewType;
 		object _footerView;
 		DataTemplate _footerViewTemplate;
@@ -301,18 +301,25 @@ namespace Microsoft.Maui.Controls.Handlers.Items
 			if (item == null)
 				return;
 
-			var sizeRequest = new SizeRequest(new Size(0, 0));
+			var size = Size.Zero;
 
-			if (item is View view)
-				sizeRequest = view.Measure(double.PositiveInfinity, double.PositiveInfinity, MeasureFlags.IncludeMargins);
+			if (item is IView view)
+			{
+				if (view.Handler == null)
+				{
+					TemplateHelpers.GetHandler(view as View, ItemsView.FindMauiContext());
+				}
+
+				size = view.Measure(double.PositiveInfinity, double.PositiveInfinity);
+			}
 
 			if (item is DataTemplate dataTemplate)
 			{
-				var content = dataTemplate.CreateContent() as View;
-				sizeRequest = content.Measure(double.PositiveInfinity, double.PositiveInfinity, MeasureFlags.IncludeMargins);
+				var content = dataTemplate.CreateContent() as IView;
+				size = content.Measure(double.PositiveInfinity, double.PositiveInfinity);
 			}
 
-			var itemHeight = (int)sizeRequest.Request.Height;
+			var itemHeight = size.Height;
 
 			if (isHeader)
 				_headerHeight = itemHeight;

src/Controls/src/Core/Handlers/Items/Android/ItemsSources/EmptySource.cs

@@ -3,7 +3,7 @@ namespace Microsoft.Maui.Controls.Handlers.Items
 {
 	sealed internal class EmptySource : IItemsViewSource
 	{
-		public int Count => 0;
+		public int Count => (HasHeader? 1 : 0) + (HasFooter? 1 : 0);
 
 		public bool HasHeader { get; set; }
 		public bool HasFooter { get; set; }

src/Controls/tests/DeviceTests/Elements/CollectionView/CollectionViewTests.Android.cs

@@ -50,5 +50,37 @@ namespace Microsoft.Maui.DeviceTests
 			// Without Exceptions here, the test has passed.
 			Assert.Equal(0, (rootPage as IPageContainer<Page>).CurrentPage.Navigation.ModalStack.Count);
 		}
+
+		[Fact]
+		public async Task NullItemsSourceDisplaysHeaderFooterAndEmptyView() 
+		{
+			SetupBuilder();
+
+			var emptyView = new Label { Text = "Empty" };
+			var header = new Label { Text = "Header" };
+			var footer = new Label { Text = "Footer" };
+
+			var collectionView = new CollectionView
+			{
+				ItemsSource = null,
+				EmptyView = emptyView,
+				Header = header,
+				Footer = footer
+			};
+
+			ContentPage contentPage = new ContentPage() { Content = collectionView };
+
+			var frame = collectionView.Frame;
+
+			await CreateHandlerAndAddToWindow<IWindowHandler>(contentPage,
+				async (_) =>
+				{
+					await WaitForUIUpdate(frame, collectionView);
+
+					Assert.True(emptyView.Height > 0, "EmptyView should be laid out");
+					Assert.True(header.Height > 0, "Header should be laid out");
+					Assert.True(footer.Height > 0, "Footer should be laid out");
+				});
+		}
 	}
 }

src/Controls/tests/DeviceTests/Elements/CollectionView/CollectionViewTests.cs

@@ -170,6 +170,66 @@ namespace Microsoft.Maui.DeviceTests
 			});
 		}
 
+		[Theory]
+		[InlineData(true, false, false)]
+		[InlineData(true, false, true)]
+		[InlineData(true, true, false)]
+		[InlineData(true, true, true)]
+		[InlineData(false, false, false)]
+		[InlineData(false, false, true)]
+		[InlineData(false, true, false)]
+		[InlineData(false, true, true)]
+		public async Task CollectionViewStructuralItems(bool hasHeader, bool hasFooter, bool hasData) 
+		{
+			SetupBuilder();
+
+			double containerHeight = 500;
+			double containerWidth = 500;
+			var layout = new Grid() { IgnoreSafeArea = true, HeightRequest = containerHeight, WidthRequest = containerWidth };
+
+			Label headerLabel = hasHeader ? new Label { Text = "header" } : null;
+			Label footerLabel = hasFooter ? new Label { Text = "footer" } : null;
+
+			var collectionView = new CollectionView
+			{
+				ItemsLayout = LinearItemsLayout.Vertical,
+				ItemTemplate = new DataTemplate(() => new Label() { HeightRequest = 20, WidthRequest = 20 }),
+				Header = headerLabel,
+				Footer = footerLabel,
+				ItemsSource = hasData ? null : new ObservableCollection<string> { "data" }
+			};
+
+			layout.Add(collectionView);
+
+			var frame = collectionView.Frame;
+
+			await CreateHandlerAndAddToWindow<LayoutHandler>(layout, async handler =>
+			{
+				await WaitForUIUpdate(frame, collectionView);
+				frame = collectionView.Frame;
+
+#if WINDOWS
+					// On Windows, the ListView pops in and changes the frame, then actually
+					// loads in the data, which updates it again. So we need to wait for the second
+					// update before checking the size
+					await WaitForUIUpdate(frame, collectionView);
+					frame = collectionView.Frame;
+#endif
+
+				if (hasHeader)
+				{
+					Assert.True(headerLabel.Height > 0);
+					Assert.True(headerLabel.Width > 0);
+				}
+
+				if (hasFooter)
+				{
+					Assert.True(footerLabel.Height > 0);
+					Assert.True(footerLabel.Width > 0);
+				}
+			});
+		}
+
 		public static IEnumerable<object[]> GenerateLayoutOptionsCombos()
 		{
 			var layoutOptions = new LayoutOptions[] { LayoutOptions.Center, LayoutOptions.Start, LayoutOptions.End, LayoutOptions.Fill };