fix(calendar): Fix decade and year view scrolling on wasm

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

@@ -6,6 +6,7 @@
 using System.Linq;
 using System.Text;
 using Windows.Foundation;
+using Windows.UI.Core;
 using Uno;
 using Uno.Extensions;
 using Uno.Extensions.Specialized;
@@ -386,7 +387,8 @@ internal void ScrollItemIntoView(int index, ScrollIntoViewAlignment alignment, d
 				sv.ChangeView(
 					horizontalOffset: null,
 					verticalOffset: newOffset,
-					zoomFactor: null);
+					zoomFactor: null,
+					forceSynchronous);
 
 				// Makes sure the container of the requested date is materialized before the end of this method
 				base_MeasureOverride(_lastLayoutedViewport.Size);
@@ -599,6 +601,7 @@ private Size base_MeasureOverride(Size availableSize)
 #endif
 				_layoutStrategy.EndMeasure();
 			}
+
 			VisibleIndicesUpdated?.Invoke(this, null);
 
 			_layoutStrategy.EstimatePanelExtent(
@@ -655,7 +658,7 @@ private static void OnEffectiveViewportChanged(FrameworkElement sender, Effectiv
 				// (We bypass the SetItemMinimumSize in the CalendarPanel_Partial.MeasureOverride if m_type is **not** CalendarPanelType.Primary)
 				that._layoutStrategy.SetViewportSize(that.GetLayoutViewport().Size, out var needsMeasure);
 
-				if (needsMeasure || Math.Abs(that._effectiveViewport.Y - that._lastLayoutedViewport.Y) > 100)
+				if (needsMeasure || Math.Abs(that._effectiveViewport.Y - that._lastLayoutedViewport.Y) > (that._lastLayoutedViewport.Height / that.Rows) * .75)
 				{
 					that.InvalidateMeasure();
 				}

src/Uno.UI/UI/Xaml/Controls/ScrollContentPresenter/ScrollContentPresenter.wasm.cs

@@ -12,6 +12,7 @@
 using Windows.Foundation;
 using Uno.UI.Xaml;
 using Microsoft.Extensions.Logging;
+using Uno.UI.Extensions;
 
 namespace Windows.UI.Xaml.Controls
 {
@@ -21,6 +22,9 @@ public partial class ScrollContentPresenter : ContentPresenter, IScrollContentPr
 		private ScrollBarVisibility _horizontalScrollBarVisibility;
 		private bool _eventsRegistered;
 
+		private (double? horizontal, double? vertical)? _pendingScrollTo;
+		private FrameworkElement _rootEltUsedToProcessScrollTo;
+
 		internal Size ScrollBarSize
 		{
 			get
@@ -179,25 +183,71 @@ private protected override void OnUnloaded()
 		{
 			base.OnUnloaded();
 			UnregisterEventHandler("scroll", (EventHandler)OnScroll, GenericEventHandlers.RaiseEventHandler);
+
+			if (_rootEltUsedToProcessScrollTo is {} rootElt)
+			{
+				rootElt.LayoutUpdated -= TryProcessScrollTo;
+				_rootEltUsedToProcessScrollTo = null;
+			}
 		}
 
-		public void ScrollTo(double? horizontalOffset, double? verticalOffset, bool disableAnimation)
-			=> WindowManagerInterop.ScrollTo(HtmlId, horizontalOffset, verticalOffset, disableAnimation);
+		/// <inheritdoc />
+		internal override void OnLayoutUpdated()
+		{
+			base.OnLayoutUpdated();
 
-		private void OnScroll(object sender, EventArgs args)
+			TryProcessScrollTo();
+		}
+
+		public void ScrollTo(double? horizontalOffset, double? verticalOffset, bool disableAnimation)
 		{
-			var left = GetProperty("scrollLeft");
-			var top = GetProperty("scrollTop");
+			_pendingScrollTo = (horizontalOffset, verticalOffset);
 
-			if (!double.TryParse(left, NumberStyles.Number, CultureInfo.InvariantCulture, out var horizontalOffset))
+			WindowManagerInterop.ScrollTo(HtmlId, horizontalOffset, verticalOffset, disableAnimation);
+
+			if (_pendingScrollTo.HasValue)
 			{
-				horizontalOffset = 0;
+				// The scroll to was not processed by the native SCP, we need to re-request ScrollTo a bit later.
+				// This happen has soon as the native SCP element is not in a valid state (like un-arranged or hidden).
+
+				if (_rootEltUsedToProcessScrollTo is null && Window.Current.RootElement is FrameworkElement rootFwElt)
+				{
+					_rootEltUsedToProcessScrollTo = rootFwElt;
+					rootFwElt.LayoutUpdated += TryProcessScrollTo;
+				}
+
+				// As the native ScrollTo is going to be async, we manually raise the event with the provided values.
+				// If those values are invalid, the browser will raise the final event anyway.
+				(TemplatedParent as ScrollViewer)?.OnScrollInternal(
+					horizontalOffset ?? GetNativeHorizontalOffset(),
+					verticalOffset ?? GetNativeVerticalOffset(),
+					isIntermediate: false
+				);
 			}
-			if (!double.TryParse(top, NumberStyles.Number, CultureInfo.InvariantCulture, out var verticalOffset))
+		}
+
+		private void TryProcessScrollTo(object sender, object e)
+			=> TryProcessScrollTo();
+
+		private void TryProcessScrollTo()
+		{
+			if (_pendingScrollTo is { } scrollTo)
+			{
+				WindowManagerInterop.ScrollTo(HtmlId, scrollTo.horizontal, scrollTo.vertical, disableAnimation: true);
+			}
+		}
+
+		private void OnScroll(object sender, EventArgs args)
+		{
+			if (IsArrangeDirty && _pendingScrollTo.HasValue)
 			{
-				verticalOffset = 0;
+				// When the native element of the SCP is becoming "valid" with a non 0 offset, it will raise a scroll event.
+				// But if we have a manual scroll request pending, we need to mute it and wait for the next layout updated.
+				return;
 			}
 
+			_pendingScrollTo = default;
+
 			// We don't have any information from the DOM 'scroll' event about the intermediate vs. final state.
 			// We could try to rely on the IsPointerPressed state to detect when the user is scrolling and use it.
 			// This would however not include scrolling due to the inertia which should also be flagged as intermediate.
@@ -210,12 +260,22 @@ private void OnScroll(object sender, EventArgs args)
 			var isIntermediate = false;
 
 			(TemplatedParent as ScrollViewer)?.OnScrollInternal(
-				horizontalOffset,
-				verticalOffset,
+				GetNativeHorizontalOffset(),
+				GetNativeVerticalOffset(),
 				isIntermediate
 			);
 		}
 
+		private double GetNativeHorizontalOffset()
+			=> double.TryParse(GetProperty("scrollLeft"), NumberStyles.Number, CultureInfo.InvariantCulture, out var horizontalOffset)
+				? horizontalOffset
+				: 0;
+
+		private double GetNativeVerticalOffset()
+			=> double.TryParse(GetProperty("scrollTop"), NumberStyles.Number, CultureInfo.InvariantCulture, out var verticalOffset)
+				? verticalOffset
+				: 0;
+
 		void IScrollContentPresenter.OnMinZoomFactorChanged(float newValue) { }
 
 		void IScrollContentPresenter.OnMaxZoomFactorChanged(float newValue) { }

src/Uno.UI/UI/Xaml/FrameworkElement.EffectiveViewport.cs

@@ -96,7 +96,7 @@ private void ReconfigureViewportPropagation(IFrameworkElement_EffectiveViewport
 				}
 				else
 				{
-					TRACE_EFFECTIVE_VIEWPORT("New child requested viewport propagation which has already been enabled. Force updating all children.");
+					TRACE_EFFECTIVE_VIEWPORT("New child requested viewport propagation which has already been enabled, forwarding current viewport to it.");
 
 					// We are already subscribed, the parent won't send any update (and our _parentViewport is expected to be up-to-date).
 					// But if this "reconfigure" was made for a new child (child != null), we have to initialize its own _parentViewport.