fix(calendar): Fix vertical stretching (most probably not on Android …

…and iOS)

src/Uno.UI.FluentTheme/Resources/PriorityDefault/CalendarView_themeresources.xaml

@@ -1,7 +1,8 @@
 <!-- Copyright (c) Microsoft Corporation. All rights reserved. Licensed under the MIT License. See LICENSE in the project root for license information. -->
 <ResourceDictionary 
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
-    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+	xmlns:uno="using:Uno.UI.Xaml.Controls">
     <ResourceDictionary.ThemeDictionaries>
         <ResourceDictionary x:Key="Default">
             <StaticResource x:Key="CalendarViewFocusBorderBrush" ResourceKey="SystemControlForegroundBaseHighBrush" />
@@ -201,6 +202,7 @@
                                 <Setter Property="TabNavigation" Value="Once" />
                                 <Setter Property="BringIntoViewOnFocusChange" Value="False" />
                                 <Setter Property="Template" Value="{StaticResource ScrollViewerScrollBarlessTemplate}" />
+								<Setter Property="(uno:ScrollViewer.ShouldFallBackToNativeScrollBars)" Value="False" />
                             </Style>
                         </Border.Resources>
                         <VisualStateManager.VisualStateGroups>

src/Uno.UI/Microsoft/UI/Xaml/Controls/CalendarView/CalendarView_themeresources.xaml

@@ -2,7 +2,8 @@
 <ResourceDictionary 
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-    xmlns:automation="clr-namespace:Windows.UI.Xaml.Automation">
+    xmlns:automation="clr-namespace:Windows.UI.Xaml.Automation"
+	xmlns:uno="using:Uno.UI.Xaml.Controls">
     <ResourceDictionary.ThemeDictionaries>
         <ResourceDictionary x:Key="Default">
             <StaticResource x:Key="CalendarViewFocusBorderBrush" ResourceKey="SystemControlForegroundBaseHighBrush" />
@@ -200,6 +201,7 @@
                                 <Setter Property="TabNavigation" Value="Once" />
                                 <Setter Property="BringIntoViewOnFocusChange" Value="False" />
                                 <Setter Property="Template" Value="{StaticResource ScrollViewerScrollBarlessTemplate}" />
+								<Setter Property="(uno:ScrollViewer.ShouldFallBackToNativeScrollBars)" Value="False" />
                             </Style>
                         </Border.Resources>
                         <VisualStateManager.VisualStateGroups>

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

@@ -15,7 +15,7 @@ namespace Windows.UI.Xaml.Controls.Primitives
 {
 	// This file is aimed to implement methods that should be implemented by the ModernCollectionBasePanel which is not present in Uno
 
-	partial class CalendarPanel : ILayoutDataInfoProvider
+	partial class CalendarPanel : ILayoutDataInfoProvider, ICustomScrollInfo
 	{
 		// The CalendarView has a minimum size of 296x350, any size under this one will trigger clipping
 		// TODO: Is this size updated according to accessibility font scale factor?
@@ -327,6 +327,13 @@ private void base_Initialize()
 			EffectiveViewportChanged += OnEffectiveViewportChanged;
 		}
 
+
+		/// <inheritdoc />
+		public double? ViewportWidth { get; private set; }
+
+		/// <inheritdoc />
+		public double? ViewportHeight { get; private set; }
+
 		#region Private and internal API required by UWP code
 		internal int FirstVisibleIndexBase { get; private set; } = -1;
 		internal int LastVisibleIndexBase { get; private set; } = -1;
@@ -554,6 +561,9 @@ private Size base_MeasureOverride(Size availableSize)
 				global::System.Diagnostics.Debug.Assert(_cache.LastIndex >= LastVisibleIndex || LastVisibleIndex == -1);
 				global::System.Diagnostics.Debug.Assert(Children.Count == _cache.LastIndex - _cache.FirstIndex + 1 || (_cache.LastIndex == -1 && _cache.LastIndex == -1));
 
+				// We force the parent ScrollViewer to use the same viewport as us, no matter its own stretching.
+				ViewportHeight = viewport.Height;
+
 				ShouldInterceptInvalidate = false;
 				_layoutStrategy.EndMeasure();
 			}
@@ -593,7 +603,7 @@ private Size base_ArrangeOverride(Size finalSize)
 
 			return finalSize;
 		}
-#endregion
+		#endregion
 
 		private static void OnEffectiveViewportChanged(FrameworkElement sender, EffectiveViewportChangedEventArgs args)
 		{

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

@@ -149,9 +149,14 @@ protected override Size MeasureOverride(Size size)
 
 				child.Measure(slotSize);
 
+				var desired = child.DesiredSize;
+
+				// Give opportunity to the the content to define the viewport size itself
+				(child as ICustomScrollInfo)?.ApplyViewport(ref desired);
+
 				return new Size(
-					Math.Min(size.Width, child.DesiredSize.Width),
-					Math.Min(size.Height, child.DesiredSize.Height)
+					Math.Min(size.Width, desired.Width),
+					Math.Min(size.Height, desired.Height)
 				);
 			}
 
@@ -170,6 +175,9 @@ protected override Size ArrangeOverride(Size finalSize)
 				childRect.Height = Math.Max(finalSize.Height, desiredSize.Height);
 
 				child.Arrange(childRect);
+
+				// Give opportunity to the the content to define the viewport size itself
+				(child as ICustomScrollInfo)?.ApplyViewport(ref finalSize);
 			}
 
 			return finalSize;

src/Uno.UI/UI/Xaml/Controls/ScrollViewer/ICustomScrollInfo.cs

@@ -0,0 +1,48 @@
+using System;
+using System.Linq;
+using Windows.Foundation;
+
+namespace Windows.UI.Xaml.Controls
+{
+	internal interface ICustomScrollInfo
+	{
+		/// <summary>
+		/// Defines the desired viewport width, if not set, fallbacks to the default algorithm.
+		/// This is used in the ScrollViewer measure and in computation of all the ScrollViewer properties.
+		/// </summary>
+		public double? ViewportWidth { get; }
+
+		/// <summary>
+		/// Defines the desired viewport height, if not set, fallbacks to the default algorithm
+		/// This is used in the ScrollViewer measure and in computation of all the ScrollViewer properties.
+		/// </summary>
+		public double? ViewportHeight { get; }
+	}
+
+	internal static class CustomScrollInfoExtensions
+	{
+		public static void ApplyViewport(this ICustomScrollInfo scrollInfo, ref Size size)
+		{
+			if (scrollInfo.ViewportWidth is { } width)
+			{
+				size.Width = width;
+			}
+			if (scrollInfo.ViewportHeight is { } height)
+			{
+				size.Height = height;
+			}
+		}
+
+		public static void ApplyViewport(this ICustomScrollInfo scrollInfo, ref Rect rect)
+		{
+			if (scrollInfo.ViewportWidth is { } width)
+			{
+				rect.Width = width;
+			}
+			if (scrollInfo.ViewportHeight is { } height)
+			{
+				rect.Height = height;
+			}
+		}
+	}
+}