feat(calendar): Enable phase loading

src/Uno.UI/DirectUI/BudgetManager.uno.cs

@@ -7,7 +7,10 @@ partial class BudgetManager
 	{
 		public int GetElapsedMilliSecondsSinceLastUITick()
 		{
-			throw new NotImplementedException();
+			// This method is use to re-dispatch a work item to the next dispatcher loop if we are about to freeze UI for too long
+			// (40 ms are allowed, cf CalendarViewGeneratorMonthViewHost.BUDGET_MANAGER_DEFAULT_LIMIT)
+
+			return 1; 
 		}
 	}
 }

src/Uno.UI/DirectUI/DXamlCore.cs

@@ -46,7 +46,10 @@ public void RegisterWork(ITreeBuilder treeBuilder)
 					return;
 				}
 
+				treeBuilder.IsRegisteredForCallbacks = false;
+
 				var workerHasWorkLeft = treeBuilder.BuildTree();
+
 				if (workerHasWorkLeft)
 				{
 					var workerReRegistered = treeBuilder.IsRegisteredForCallbacks;

src/Uno.UI/Microsoft/UI/Xaml/Controls/CalendarView/CalendarViewDayItem.cs

@@ -56,7 +56,7 @@ internal CalendarViewDayItemChangingEventArgs GetBuildTreeArgs()
 			{
 				CalendarViewDayItemChangingEventArgs spArgs;
 
-				spArgs = default;
+				spArgs = new CalendarViewDayItemChangingEventArgs();
 				m_tpBuildTreeArgs = spArgs;
 				pspArgs = spArgs;
 			}

src/Uno.UI/Microsoft/UI/Xaml/Controls/CalendarView/CalendarViewGeneratorHost.cs

@@ -160,7 +160,7 @@ internal virtual void PrepareItemContainer(
 			return;
 		}
 
-		internal void ClearContainerForItem(
+		internal virtual void ClearContainerForItem(
 			DependencyObject pContainer,
 			object pItem)
 		{

src/Uno.UI/Microsoft/UI/Xaml/Controls/CalendarView/CalendarViewGeneratorHost.h.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using Windows.Foundation;
 using Windows.Globalization;
 using Windows.UI.Xaml.Controls.Primitives;
 using Windows.UI.Xaml.Data;
@@ -14,5 +15,17 @@ partial class CalendarViewGeneratorHost : IDirectManipulationStateChangeHandler
 		internal DateTime GetMinDateOfCurrentScope() { return m_minDateOfCurrentScope; }
 		internal DateTime GetMaxDateOfCurrentScope() { return m_maxDateOfCurrentScope; }
 		internal string GetHeaderTextOfCurrentScope() { return m_pHeaderText; }
+
+		internal virtual void SetupContainerContentChangingAfterPrepare(
+			DependencyObject pContainer,
+			object pItem,
+			int itemIndex,
+			Size measureSize)
+		{ }
+
+		internal virtual void RaiseContainerContentChangingOnRecycle(
+			UIElement pContainer,
+			object pItem)
+		{ }
 	}
 }

src/Uno.UI/Microsoft/UI/Xaml/Controls/CalendarView/CalendarViewGeneratorMonthViewHost.cs

@@ -137,7 +137,7 @@ internal override void UpdateLabel(CalendarViewBaseItem pItem, bool isLabelVisib
 		}
 
 		// reset CIC event if the container is being cleared.
-		private void ClearContainerForItem(
+		internal override void ClearContainerForItem(
 			DependencyObject pContainer,
 			object pItem)
 		{

src/Uno.UI/Microsoft/UI/Xaml/Controls/CalendarView/CalendarViewGeneratorMonthViewHost_ContainerPhase.cs

@@ -1,3 +1,5 @@
+#nullable enable
+
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License. See LICENSE in the project root for license information.
 
@@ -18,9 +20,9 @@ partial class CalendarViewGeneratorMonthViewHost : ITreeBuilder
 		// the CalendarView version removes UIPlaceHolder and handles blackout state.
 		// Other logicals are still same as ListViewBase.
 
-		private void SetupContainerContentChangingAfterPrepare(
+		internal override void SetupContainerContentChangingAfterPrepare(
 			DependencyObject pContainer,
-			DependencyObject pItem,
+			object pItem,
 			int itemIndex,
 			Size measureSize)
 		{
@@ -49,6 +51,12 @@ private void SetupContainerContentChangingAfterPrepare(
 				spArgsConcrete = spArgs as CalendarViewDayItemChangingEventArgs;
 			}
 
+			// Uno only null-ref fix:
+			if (pVirtualizationInformation is null || spArgsConcrete is null)
+			{
+				return;
+			}
+
 			// store the size we would measure with
 			pVirtualizationInformation.MeasureSize = measureSize;
 
@@ -202,9 +210,9 @@ bool ITreeBuilder.BuildTree()
 			return pWorkLeft;
 		}
 
-		private void RaiseContainerContentChangingOnRecycle(
+		internal override void RaiseContainerContentChangingOnRecycle(
 			UIElement pContainer,
-			DependencyObject pItem)
+			object pItem)
 		{
 			CalendarViewDayItemChangingEventArgs spArgs;
 			CalendarViewDayItemChangingEventArgs spArgsConcrete;

src/Uno.UI/Microsoft/UI/Xaml/Controls/CalendarView/Primitives/CalendarPanel.ModernCollectionBasePanel.cs

@@ -181,7 +181,7 @@ internal IEnumerable<CacheEntry> CompleteGeneration(int endIndex)
 				return unusedEntries;
 			}
 
-			internal (UIElement container, bool isNew) GetOrCreate(int index)
+			internal (CacheEntry entry, CacheEntryKind kind) GetOrCreate(int index)
 			{
 				Debug.Assert(_host is { });
 				Debug.Assert(_generationStartIndex <= index);
@@ -223,7 +223,7 @@ internal IEnumerable<CacheEntry> CompleteGeneration(int endIndex)
 
 						Debug.Assert(entry.Index == index);
 
-						return (entry.Container, false);
+						return (entry, CacheEntryKind.Kept);
 					}
 
 					case GenerationState.Before:
@@ -233,19 +233,19 @@ internal IEnumerable<CacheEntry> CompleteGeneration(int endIndex)
 						var item = _host![index];
 
 						CacheEntry entry;
-						bool isNew;
+						CacheEntryKind kind;
 						if (_generationRecyclableBefore.count > 0)
 						{
 							entry = _entries[_generationRecyclableBefore.at];
-							isNew = false;
+							kind = CacheEntryKind.Recycled;
 
 							_generationRecyclableBefore.at++;
 							_generationRecyclableBefore.count--;
 						}
 						else if (_generationRecyclableAfter.count > 0)
 						{
 							entry = _entries[_generationRecyclableAfter.at + _generationRecyclableAfter.count - 1];
-							isNew = false;
+							kind = CacheEntryKind.Recycled;
 
 							_generationRecyclableAfter.count--;
 
@@ -255,7 +255,7 @@ internal IEnumerable<CacheEntry> CompleteGeneration(int endIndex)
 						{
 							var container = (UIElement)_host.GetContainerForItem(item, null);
 							entry = new CacheEntry(container);
-							isNew = true;
+							kind = CacheEntryKind.New;
 
 							_entries.Add(entry);
 						}
@@ -265,7 +265,7 @@ internal IEnumerable<CacheEntry> CompleteGeneration(int endIndex)
 
 						_host.PrepareItemContainer(entry.Container, item);
 
-						return (entry.Container, isNew);
+						return (entry, kind);
 					}
 				}
 
@@ -309,6 +309,13 @@ private class CacheEntryComparer : IComparer<CacheEntry>
 			public int Compare(CacheEntry x, CacheEntry y) => x.Index.CompareTo(y.Index);
 		}
 
+		private enum CacheEntryKind
+		{
+			New,
+			Kept,
+			Recycled
+		}
+
 		internal event VisibleIndicesUpdatedEventCallback VisibleIndicesUpdated;
 
 		private readonly ContainersCache _cache = new ContainersCache();
@@ -328,8 +335,8 @@ private void base_Initialize()
 		#region Private and internal API required by UWP code
 		internal int FirstVisibleIndexBase { get; private set; }
 		internal int LastVisibleIndexBase { get; private set; }
-		internal int FirstCacheIndexBase { get; private set; }
-		internal int LastCacheIndexBase { get; private set; }
+		internal int FirstCacheIndexBase => _cache.StartIndex;
+		internal int LastCacheIndexBase => _cache.EndIndex;
 
 		[NotImplemented]
 		internal PanelScrollingDirection PanningDirectionBase { get; } = PanelScrollingDirection.None;
@@ -370,14 +377,10 @@ internal void ScrollItemIntoView(int index, ScrollIntoViewAlignment alignment, d
 		}
 
 		private Size GetViewportSize()
-		{
-			return _lastLayoutedViewport.Size.AtLeast(_defaultHardCodedSize).FiniteOrDefault(_defaultHardCodedSize);
-		}
+			=> _lastLayoutedViewport.Size.AtLeast(_defaultHardCodedSize).FiniteOrDefault(_defaultHardCodedSize);
 
 		internal Size GetDesiredViewportSize()
-		{
-			return _layoutStrategy.GetDesiredViewportSize();
-		}
+			=> _layoutStrategy?.GetDesiredViewportSize() ?? default;
 
 		[NotImplemented]
 		internal void GetTargetIndexFromNavigationAction(
@@ -396,9 +399,7 @@ internal void GetTargetIndexFromNavigationAction(
 		}
 
 		internal IItemContainerMapping GetItemContainerMapping()
-		{
-			throw new NotImplementedException();
-		}
+			=> _cache;
 
 		private void SetLayoutStrategyBase(CalendarLayoutStrategy spLayoutStrategy)
 		{
@@ -463,10 +464,10 @@ private Size base_MeasureOverride(Size availableSize)
 						|| _layoutStrategy.ShouldContinueFillingUpSpace(ElementType.ItemContainer, index, layout, remainingWindowToFill))
 					)
 				{
-					var (container, isNew) = _cache.GetOrCreate(index);
-					if (isNew)
+					var (entry, kind) = _cache.GetOrCreate(index);
+					if (kind == CacheEntryKind.New)
 					{
-						Children.Add(container);
+						Children.Add(entry.Container);
 					}
 
 					var itemSize = _layoutStrategy.GetElementMeasureSize(ElementType.ItemContainer, index, renderWindow); // Note: It's actually the same for all items
@@ -480,8 +481,19 @@ private Size base_MeasureOverride(Size availableSize)
 						return default;
 					}
 
-					container.Measure(itemSize);
-					container.GetVirtualizationInformation().MeasureSize = itemSize;
+					entry.Container.Measure(itemSize);
+					entry.Container.GetVirtualizationInformation().MeasureSize = itemSize;
+					switch (kind)
+					{
+						case CacheEntryKind.New:
+							_host.SetupContainerContentChangingAfterPrepare(entry.Container, entry.Item, entry.Index, itemSize);
+							break;
+
+						case CacheEntryKind.Recycled:
+							// Note: ModernBasePanel seems to use only SetupContainerContentChangingAfterPrepare
+							_host.RaiseContainerContentChangingOnRecycle(entry.Container, entry.Item);
+							break;
+					}
 
 					var isVisible = viewport.Contains(itemBounds.Location);
 					if (firstVisibleIndex == -1 && isVisible)