fix(listview): [WASM] [Skia] [macOS] Improve ListView measurement

Do item arrangement on the Arrange pass for the managed ListView implementation. This is important for consistency with WinUI in certain layout configurations.

src/Uno.UI/UI/Xaml/Controls/ContentControl/ContentControl.cs

@@ -57,16 +57,27 @@ public partial class ContentControl : Control, IEnumerable
 
 		protected override bool CanCreateTemplateWithoutParent { get { return _canCreateTemplateWithoutParent; } }
 
+		private VirtualizationInformation? _virtualizationInformation;
+		internal VirtualizationInformation GetVirtualizationInformation() => _virtualizationInformation ??= new VirtualizationInformation();
+
 		/// <summary>
 		/// Marks this control as a container generated by, eg, a <see cref="Primitives.Selector"/>, rather than an element explicitly 
 		/// defined in xaml.
 		/// </summary>
-		internal bool IsGeneratedContainer { get; set; }
+		internal bool IsGeneratedContainer
+		{
+			get => _virtualizationInformation?.IsGeneratedContainer ?? false;
+			set => GetVirtualizationInformation().IsGeneratedContainer = value;
+		}
 
 		/// <summary>
 		/// Marks this as a container defined in the root of an ItemTemplate, so that it can be handled appropriately when recycled.
 		/// </summary>
-		internal bool IsContainerFromItemTemplate { get; set; }
+		internal bool IsContainerFromTemplateRoot
+		{
+			get => _virtualizationInformation?.IsContainerFromTemplateRoot ?? false;
+			set => GetVirtualizationInformation().IsContainerFromTemplateRoot = value;
+		}
 
 #nullable disable // Public members should stay nullable-oblivious for now to stay consistent with WinUI
 		public ContentControl()

src/Uno.UI/UI/Xaml/Controls/ItemsControl/ItemsControl.cs

@@ -1063,7 +1063,7 @@ object GetContent()
 					containerAsContentControl.Style = styleFromItemsControl;
 				}
 
-				if (!containerAsContentControl.IsContainerFromItemTemplate)
+				if (!containerAsContentControl.IsContainerFromTemplateRoot)
 				{
 					containerAsContentControl.ContentTemplate = ItemTemplate;
 					containerAsContentControl.ContentTemplateSelector = ItemTemplateSelector;
@@ -1078,7 +1078,7 @@ object GetContent()
 					// the result of the fallback value of the binding set below.
 					containerAsContentControl.DataContext = GetContent();
 
-					if (!containerAsContentControl.IsContainerFromItemTemplate && containerAsContentControl.GetBindingExpression(ContentControl.ContentProperty) == null)
+					if (!containerAsContentControl.IsContainerFromTemplateRoot && containerAsContentControl.GetBindingExpression(ContentControl.ContentProperty) == null)
 					{
 						containerAsContentControl.SetBinding(ContentControl.ContentProperty, new Binding());
 					}

src/Uno.UI/UI/Xaml/Controls/ItemsStackPanel/ItemsStackPanelLayout.managed.cs

@@ -3,7 +3,9 @@
 using System.Collections.Generic;
 using System.Text;
 using Uno.UI;
+using Windows.Foundation;
 using Windows.UI.Xaml.Controls.Primitives;
+using static System.Math;
 
 namespace Windows.UI.Xaml.Controls
 {
@@ -28,6 +30,25 @@ protected override Line CreateLine(GeneratorDirection fillDirection, double exte
 		}
 
 		protected override int GetItemsPerLine() => 1;
+
+		protected override Rect GetElementArrangeBounds(int elementIndex, Rect containerBounds, Size windowConstraint, Size finalSize)
+		{
+			// we will give the container what it requested if bigger than the constraint, and let the clipping occur by the scrollviewer
+			// we will give the container the constraint of the window (the viewport really) so that it can be laid out inside of the 
+			// viewport. Basically this means that a bigger container does not influence the alignment of smaller elements.
+			// we do not use the finalsize, because that will represent the largest element in the viewport.
+			var breadth = Max(GetBreadth(containerBounds), GetBreadth(windowConstraint));
+
+			// unfortunate, but incorrectly configured panels (for instance, panel is set to orient horizontally, where scrollviewer is set to enable scrolling vertically
+			// will potentially have infinity here. Also, the listview itself might have been inside of scrollviewer that allowed infinite in this direction
+			breadth = Min(breadth, GetBreadth(finalSize));
+			SetBreadth(ref containerBounds, breadth);
+
+			// Uno TODO
+			// result.* SizeFromRectInNonVirtualizingDirection() -= GetGroupPaddingAtStart().* SizeInNonVirtualizingDirection() + GetGroupPaddingAtEnd().* SizeInNonVirtualizingDirection();
+
+			return containerBounds;
+		}
 	}
 }
 

src/Uno.UI/UI/Xaml/Controls/ListViewBase/VirtualizingPanelLayout.cs

@@ -139,23 +139,23 @@ public bool ShouldBreadthStretch
 		{
 			get
 			{
-				if (XamlParent == null)
+				var stretchOwner =
+#if !__IOS__ && !__ANDROID__
+					IsInsidePopup ? (FrameworkElement)OwnerPanel :
+#endif
+					XamlParent;
+				if (stretchOwner == null)
 				{
 					return true;
 				}
 
-				if (IsInsidePopup)
-				{
-					return false;
-				}
-
 				if (ScrollOrientation == Orientation.Vertical)
 				{
-					return XamlParent.HorizontalAlignment == HorizontalAlignment.Stretch;
+					return stretchOwner.HorizontalAlignment == HorizontalAlignment.Stretch;
 				}
 				else
 				{
-					return XamlParent.VerticalAlignment == VerticalAlignment.Stretch;
+					return stretchOwner.VerticalAlignment == VerticalAlignment.Stretch;
 				}
 			}
 		}

src/Uno.UI/UI/Xaml/Controls/ListViewBase/VirtualizingPanelLayout.managed.cs

@@ -252,6 +252,7 @@ private void OnScrollChanged(object sender, ScrollViewerViewChangedEventArgs e)
 				unappliedDelta = Max(0, unappliedDelta);
 				UpdateLayout(extentAdjustment: sign * -unappliedDelta);
 			}
+			ArrangeElements(_availableSize, ViewportSize);
 			UpdateCompleted();
 
 			_lastScrollOffset = ScrollOffset;
@@ -272,7 +273,7 @@ private double GetScrollConsumptionIncrement(GeneratorDirection fillDirection)
 				return _averageLineHeight;
 			}
 
-			return GetExtent(incrementView);
+			return GetActualExtent(incrementView);
 		}
 
 		internal Size MeasureOverride(Size availableSize)
@@ -308,7 +309,7 @@ internal Size ArrangeOverride(Size finalSize)
 			{
 				if (this.Log().IsEnabled(LogLevel.Debug))
 				{
-					this.Log().LogDebug("Measured without an ItemsControl: simply return size(0,0) for now...");
+					this.Log().LogDebug("Arranged without an ItemsControl: simply return size(0,0) for now...");
 				}
 
 				return new Size(0, 0);
@@ -321,11 +322,28 @@ internal Size ArrangeOverride(Size finalSize)
 			}
 
 			_availableSize = finalSize;
-			UpdateLayout(extentAdjustment: _scrollAdjustmentForCollectionChanges);
+			var adjustedVisibleWindow = ViewportSize;
+			ArrangeElements(finalSize, adjustedVisibleWindow);
 
 			return EstimatePanelSize(isMeasure: false);
 		}
 
+		private void ArrangeElements(Size finalSize, Size adjustedVisibleWindow)
+		{
+			foreach (var line in _materializedLines)
+			{
+				var indexAdjustment = -1;
+				foreach (var view in line.ContainerViews)
+				{
+					indexAdjustment++;
+
+					var bounds = GetBoundsForElement(view);
+					var arrangedBounds = GetElementArrangeBounds(line.FirstItemFlat + indexAdjustment, bounds, adjustedVisibleWindow, finalSize);
+					view.Arrange(arrangedBounds);
+				}
+			}
+		}
+
 		/// <summary>
 		/// Update the item container layout by removing no-longer-visible views and adding visible views.
 		/// </summary>
@@ -419,7 +437,7 @@ private void UnfillLayout(double extentAdjustment)
 			void UnfillBackward()
 			{
 				var firstMaterializedLine = GetFirstMaterializedLine();
-				while (firstMaterializedLine != null && GetEnd(firstMaterializedLine.FirstView) < ExtendedViewportStart + extentAdjustment)
+				while (firstMaterializedLine != null && GetMeasuredEnd(firstMaterializedLine.FirstView) < ExtendedViewportStart + extentAdjustment)
 				{
 					// Dematerialize lines that are entirely outside extended viewport
 					RecycleLine(firstMaterializedLine);
@@ -431,7 +449,7 @@ void UnfillBackward()
 			void UnfillForward()
 			{
 				var lastMaterializedLine = GetLastMaterializedLine();
-				while (lastMaterializedLine != null && GetStart(lastMaterializedLine.FirstView) > ExtendedViewportEnd + extentAdjustment)
+				while (lastMaterializedLine != null && GetMeasuredStart(lastMaterializedLine.FirstView) > ExtendedViewportEnd + extentAdjustment)
 				{
 					// Dematerialize lines that are entirely outside extended viewport
 					RecycleLine(lastMaterializedLine);
@@ -617,12 +635,11 @@ private double EstimatePanelExtent()
 
 		private void UpdateAverageLineHeight()
 		{
-			_averageLineHeight = _materializedLines.Count > 0 ? _materializedLines.Select(l => GetExtent(l.FirstView)).Average()
+			_averageLineHeight = _materializedLines.Count > 0 ? _materializedLines.Select(l => GetMeasuredExtent(l.FirstView)).Average()
 				: 0;
 		}
 
-		private double CalculatePanelMeasureBreadth() => ShouldMeasuredBreadthStretch ? AvailableBreadth :
-					_materializedLines.Select(l => GetDesiredBreadth(l.FirstView)).MaxOrDefault()
+		private double CalculatePanelMeasureBreadth() => _materializedLines.Select(l => GetDesiredBreadth(l.FirstView)).MaxOrDefault()
 #if __WASM__
 			+ GetBreadth(XamlParent.ScrollViewer.ScrollBarSize)
 #endif
@@ -796,26 +813,29 @@ protected void AddView(FrameworkElement view, GeneratorDirection fillDirection,
 				new Point(breadthOffset, extentOffset + extentOffsetAdjustment) :
 				new Point(extentOffset + extentOffsetAdjustment, breadthOffset);
 
-			var adjustedDesiredSize = ScrollOrientation == Orientation.Vertical
-				? new Size(
-					ShouldMeasuredBreadthStretch ? AvailableBreadth :
-					(_lastMeasuredSize != default ? GetBreadth(_lastMeasuredSize) : view.DesiredSize.Width),
-					view.DesiredSize.Height
-				)
-				: new Size(
-					view.DesiredSize.Width,
-					ShouldMeasuredBreadthStretch ? AvailableBreadth :
-					(_lastMeasuredSize != default ? GetBreadth(_lastMeasuredSize) : view.DesiredSize.Height)
-				);
-
-			var finalRect = new Rect(topLeft, adjustedDesiredSize);
+			// TODO: GetElementBounds()
+			var finalRect = new Rect(topLeft, view.DesiredSize);
 
 			if (this.Log().IsEnabled(LogLevel.Debug))
 			{
-				this.Log().LogDebug($"{GetMethodTag()} finalRect={finalRect} AvailableBreadth={AvailableBreadth} adjustedDesiredSize={adjustedDesiredSize} DC={view.DataContext}");
+				this.Log().LogDebug($"{GetMethodTag()} finalRect={finalRect} AvailableBreadth={AvailableBreadth} DesiredSize={view.DesiredSize} DC={view.DataContext}");
 			}
 
-			view.Arrange(finalRect);
+			SetBounds(view, finalRect);
+		}
+
+		protected abstract Rect GetElementArrangeBounds(/*TODO ElementType, */int elementIndex, Rect containerBounds, Size windowConstraint, Size finalSize);
+
+		private void SetBounds(FrameworkElement view, Rect bounds)
+		{
+			if (view is ContentControl container)
+			{
+				container.GetVirtualizationInformation().Bounds = bounds;
+			}
+			else if (this.Log().IsEnabled(LogLevel.Warning))
+			{
+				this.Log().LogWarning($"Non-ContentControl containers aren't supported for virtualizing panel types.");
+			}
 		}
 
 		private Line? GetFirstMaterializedLine() => _materializedLines.Count > 0 ? _materializedLines[0] : null;
@@ -831,7 +851,7 @@ protected void AddView(FrameworkElement view, GeneratorDirection fillDirection,
 			var firstView = GetFirstMaterializedLine()?.FirstView;
 			if (firstView != null)
 			{
-				return GetStart(firstView);
+				return GetMeasuredStart(firstView);
 			}
 
 			return null;
@@ -842,7 +862,7 @@ protected void AddView(FrameworkElement view, GeneratorDirection fillDirection,
 			var lastView = GetLastMaterializedLine()?.LastView;
 			if (lastView != null)
 			{
-				return GetEnd(lastView);
+				return GetMeasuredEnd(lastView);
 			}
 
 			// This will be null except immediately after ScrapLayout(), when it will be the previous start of materialized items
@@ -853,37 +873,82 @@ protected void AddView(FrameworkElement view, GeneratorDirection fillDirection,
 
 		private double GetContentEnd() => GetItemsEnd() ?? 0;
 
-		private double GetStart(FrameworkElement child)
+		private double GetMeasuredStart(FrameworkElement child)
 		{
-			var offset = GetRelativePosition(child);
+			var bounds = GetBoundsForElement(child);
+
 			return ScrollOrientation == Orientation.Vertical ?
-				offset.Y - child.Margin.Top :
-				offset.X - child.Margin.Left;
+				bounds.Top :
+				bounds.Left;
 		}
 
-		private double GetEnd(FrameworkElement child)
+		private double GetMeasuredEnd(FrameworkElement child)
 		{
-			var offset = GetRelativePosition(child);
+			var bounds = GetBoundsForElement(child);
+
 			return ScrollOrientation == Orientation.Vertical ?
-				offset.Y + child.ActualHeight + child.Margin.Bottom :
-				offset.X + child.ActualWidth + child.Margin.Right;
+				bounds.Bottom :
+				bounds.Right;
 		}
 
-		private double GetExtent(FrameworkElement child)
+		private double GetMeasuredExtent(FrameworkElement child)
 		{
+			var bounds = GetBoundsForElement(child);
+
 			return ScrollOrientation == Orientation.Vertical ?
-				child.ActualHeight + child.Margin.Top + child.Margin.Bottom :
-				child.ActualWidth + child.Margin.Left + child.Margin.Right;
+				bounds.Height :
+				bounds.Width;
+
+		}
+
+		private double GetActualExtent(FrameworkElement child)
+		{
+			return ScrollOrientation == Orientation.Vertical ?
+				child.ActualHeight :
+				child.ActualWidth;
+		}
+
+		private Rect GetBoundsForElement(FrameworkElement child)
+		{
+			if (!(child is ContentControl container))
+			{
+				if (this.Log().IsEnabled(LogLevel.Warning))
+				{
+					this.Log().LogWarning($"Non-ContentControl containers aren't supported for virtualizing panel types.");
+				}
+
+				return default;
+			}
+
+			return container.GetVirtualizationInformation().Bounds;
+
 		}
 
 		private double GetExtent(Size size) => ScrollOrientation == Orientation.Vertical ?
 			size.Height :
 			size.Width;
 
-		private double GetBreadth(Size size) => ScrollOrientation == Orientation.Vertical ?
+		protected double GetBreadth(Size size) => ScrollOrientation == Orientation.Vertical ?
 			size.Width :
 			size.Height;
 
+		protected double GetBreadth(Rect rect) => ScrollOrientation == Orientation.Vertical ?
+			rect.Width :
+			rect.Height;
+
+		protected void SetBreadth(ref Rect rect, double breadth)
+		{
+			if (ScrollOrientation == Orientation.Vertical)
+			{
+				rect.Width = breadth;
+			}
+			else
+			{
+				rect.Height = breadth;
+			}
+		}
+
+
 		private double GetActualBreadth(FrameworkElement view) => ScrollOrientation == Orientation.Vertical ?
 			view.ActualWidth :
 			view.ActualHeight;

src/Uno.UI/UI/Xaml/Controls/Primitives/Selector.cs

@@ -508,7 +508,7 @@ private protected override DependencyObject GetRootOfItemTemplateAsContainer(Dat
 					// The container has been created from a template and can be recycled, so we mark it as generated
 					contentControl.IsGeneratedContainer = true;
 
-					contentControl.IsContainerFromItemTemplate = true;
+					contentControl.IsContainerFromTemplateRoot = true;
 				}
 
 				return templateRoot as DependencyObject;

src/Uno.UI/UI/Xaml/VirtualizationInformation.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Windows.Foundation;
+
+namespace Windows.UI.Xaml
+{
+	/// <summary>
+	/// Class that holds virtualization information. We do not create this class indiscriminately, but only
+	// for containers that happen to be virtualizing.
+	/// </summary>
+	internal sealed class VirtualizationInformation
+	{
+		/// <summary>
+		/// Marks this as a container generated by, eg, a <see cref="Controls.Primitives.Selector"/>, rather than an element explicitly 
+		/// defined in xaml.
+		/// </summary>
+		public bool IsGeneratedContainer { get; set; }
+
+		/// <summary>
+		/// Marks this as a container defined in the root of an ItemTemplate, so that it can be handled appropriately when recycled.
+		/// </summary>
+		public bool IsContainerFromTemplateRoot { get; set; }
+
+		public Rect Bounds { get; set; }
+	}
+}