From 926a0025c0d83dcfc6bcea4daa3fed50b5ef2788 Mon Sep 17 00:00:00 2001
From: Mike Corsaro <corsarom@gmail.com>
Date: Wed, 22 Nov 2023 14:20:41 -0800
Subject: [PATCH] [Windows] Address CollectionView virtualization (#18813)

* Add hard value for height w/ ItemContent control to partially allow virtualization to work

* Update test to be more robust

* Add real-width for ItemContentControl

---------

Co-authored-by: Mike Corsaro <mikecorsaro@microsoft.com>
---
 .../CollectionView/ItemContentControl.cs      |  6 ++
 .../CollectionViewTests.Windows.cs            | 61 +++++++++++++++++++
 2 files changed, 67 insertions(+)

diff --git a/src/Controls/src/Core/Platform/Windows/CollectionView/ItemContentControl.cs b/src/Controls/src/Core/Platform/Windows/CollectionView/ItemContentControl.cs
index 22a4449f7c86..4be1e9dedf38 100644
--- a/src/Controls/src/Core/Platform/Windows/CollectionView/ItemContentControl.cs
+++ b/src/Controls/src/Core/Platform/Windows/CollectionView/ItemContentControl.cs
@@ -284,6 +284,12 @@ protected override WSize MeasureOverride(WSize availableSize)
 		{
 			if (_renderer == null)
 			{
+				// Make sure we supply a real number for sizes otherwise virtualization won't function
+				if (double.IsFinite(availableSize.Width) && !double.IsFinite(availableSize.Height))
+					return new WSize(availableSize.Width, 32);
+				else if (!double.IsFinite(availableSize.Width) && double.IsFinite(availableSize.Height))
+					return new WSize(88, availableSize.Height);
+
 				return base.MeasureOverride(availableSize);
 			}
 
diff --git a/src/Controls/tests/DeviceTests/Elements/CollectionView/CollectionViewTests.Windows.cs b/src/Controls/tests/DeviceTests/Elements/CollectionView/CollectionViewTests.Windows.cs
index a4eb1e2f914f..cedafb04aa28 100644
--- a/src/Controls/tests/DeviceTests/Elements/CollectionView/CollectionViewTests.Windows.cs
+++ b/src/Controls/tests/DeviceTests/Elements/CollectionView/CollectionViewTests.Windows.cs
@@ -4,6 +4,7 @@
 using Microsoft.Maui.Controls;
 using Microsoft.Maui.Controls.Handlers.Items;
 using Microsoft.Maui.Handlers;
+using Microsoft.Maui.Platform;
 using Microsoft.UI.Xaml;
 using Xunit;
 using WSetter = Microsoft.UI.Xaml.Setter;
@@ -101,6 +102,66 @@ void ValidateItemContainerStyle(CollectionView collectionView)
 			Assert.Equal(0d, minHeight);
 		}
 
+		[Fact]
+		public async Task ValidateItemsVirtualize()
+		{
+			SetupBuilder();
+
+			const int listItemCount = 1000;
+
+			var collectionView = new CollectionView()
+			{
+				ItemTemplate = new Controls.DataTemplate(() =>
+				{
+					var template = new Grid()
+					{
+						ColumnDefinitions = new ColumnDefinitionCollection(
+						[
+							new ColumnDefinition(25),
+							new ColumnDefinition(25),
+							new ColumnDefinition(25),
+							new ColumnDefinition(25),
+							new ColumnDefinition(25),
+						])
+					};
+
+					for (int i = 0; i < 5; i++)
+					{
+						var label = new Label();
+						label.SetBinding(Label.TextProperty, new Binding("Symbol"));
+						Grid.SetColumn(label, i);
+						template.Add(label);
+					}
+
+					return template;
+				}),
+				ItemsSource = Enumerable.Range(0, listItemCount)
+					.Select(x => new { Symbol = x })
+					.ToList()
+			};
+
+			await CreateHandlerAndAddToWindow<CollectionViewHandler>(collectionView, async handler =>
+			{
+				var listView = (UI.Xaml.Controls.ListView)collectionView.Handler.PlatformView;
+
+				int childCount = 0;
+				int prevChildCount = -1;
+
+				await Task.Delay(2000);
+
+				await AssertionExtensions.Wait(() =>
+				{
+					// Wait until the list stops growing
+					prevChildCount = childCount;
+					childCount = listView.GetChildren<UI.Xaml.Controls.TextBlock>().Count();
+					return childCount == prevChildCount;
+				}, 10000);
+
+				// If this is broken we'll get way more than 1000 elements
+				Assert.True(childCount < 1000);
+			});
+		}
+
 		[Fact]
 		public async Task ValidateSendRemainingItemsThresholdReached()
 		{