test: startIndex approach

src/Uno.UI/UI/Xaml/Controls/CalendarView/CalendarView_Partial.cs

@@ -1649,34 +1649,6 @@ namespace Microsoft.UI.Xaml.Controls
 			global::System.Diagnostics.Debug.Assert(index >= 0);
 			global::System.Diagnostics.Debug.Assert(pHost.Panel is { });
 
-			if (pHost is CalendarViewGeneratorDecadeViewHost)
-			{
-				var rowsToMax = (MaxDate.Year - date.Year) / m_colsInYearDecadeView;
-
-				if (rowsToMax <= m_rowsInYearDecadeView / 2)
-				{
-					index -= m_rowsInYearDecadeView - rowsToMax;
-
-					int maxItemsInView = m_rowsInYearDecadeView * m_colsInYearDecadeView;
-
-					// when the last displayed date year is near the MaxDate.Year the index is offset too much
-					if (m_lastDisplayedDate.Year >= MaxDate.AddYears(-maxItemsInView).Year)
-					{
-						index -= m_rowsInYearDecadeView;
-					}
-				}
-			}
-
-			if (pHost is CalendarViewGeneratorYearViewHost && date.Year == MaxDate.Year)
-			{
-				var rowsToMax = (MaxDate.Month - date.Month) / m_colsInYearDecadeView;
-
-				if (rowsToMax <= m_rowsInYearDecadeView / 2)
-				{
-					index -= m_rowsInYearDecadeView - rowsToMax;
-				}
-			}
-
 			pHost.Panel.ScrollItemIntoView(
 				index,
 				ScrollIntoViewAlignment.Leading,

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

@@ -564,6 +564,22 @@ namespace Microsoft.UI.Xaml.Controls.Primitives
 				renderWindow.Size = requestedRenderingWindow.Size; // The renderWindow contains only position information
 				startIndex = Math.Max(0, startIndex - StartIndex);
 
+				if (Rows > 0 && Cols > 0)
+				{
+					var maxItemsInView = Rows * Cols;
+					var totalYears = _host.Owner.MaxDate.Year - _host.Owner.MinDate.Year;
+
+					if (_host is CalendarViewGeneratorDecadeViewHost && startIndex >= totalYears - maxItemsInView)
+					{
+						startIndex = totalYears - maxItemsInView;
+					}
+					else if (_host is CalendarViewGeneratorYearViewHost && startIndex >= totalYears * 12 - maxItemsInView)
+					{
+						// TODO: find a way to get number of months in calendar so we can replace magic number
+						startIndex = totalYears * 12 - maxItemsInView;
+					}
+				}
+
 				// Prepare the items generator to generate some new items (will also set which items can be recycled in this measure pass).
 				var expectedItemsCount = LastVisibleIndex - FirstVisibleIndex;
 				_cache.BeginGeneration(startIndex, startIndex + expectedItemsCount);