feat(mobile): use animation for LVB.ScrollIntoView

doc/articles/feature-flags.md

@@ -10,6 +10,13 @@ By default, this mode is enabled for the time being, as it is quite disrupting.
 Use `Uno.UI.FeatureConfiguration.UIElement.UseLegacyClipping` to control this mode.
 Additionally, `Uno.UI.FeatureConfiguration.UIElement.ShowClippingBounds` can be used to show the clipping boundaries to determine if the behavior of the clipping is appropriate.
 
+## ListView Scrolling
+
+On iOS and Android platforms specifically, `ListView.ScrollIntoView` performs an animated scrolling instead of an instant scrolling than other platforms.
+
+This feature can be toggled with: `Uno.UI.FeatureConfiguration.ListViewBase.AnimateScrollIntoView`.
+Alternatively, `Uno.UI.Helpers.ListViewHelper` offer two extension methods, `InstantScrollToIndex` and `SmoothScrollToIndex`, to perform a specific type of scrolling irrespective of the flag set.
+
 # UWP Styles default
 
 By default, Uno favors the default UWP XAML styles over the native styles for Button, Slider, ComboBox, etc...

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Controls/Given_ListViewBase.cs

@@ -2476,7 +2476,7 @@ public async Task When_Smooth_Scrolling()
 			Assert.IsTrue(count < source.Length, $"Native ListView is not {(count.HasValue ? $"virtualized (count={count})" : "loaded")}.");
 
 			// scroll to bottom
-			Uno.UI.Helpers.ListViewHelper.SmoothScroll(lv, lv.Items.Count - 1);
+			Uno.UI.Helpers.ListViewHelper.SmoothScrollToIndex(lv, lv.Items.Count - 1);
 			await Task.Delay(2000);
 			await WindowHelper.WaitForIdle();
 

src/Uno.UI/FeatureConfiguration.cs

@@ -323,6 +323,18 @@ public static class ListViewBase
 			/// the default value at the UWP default of 4.0.
 			/// </summary>
 			public static double? DefaultCacheLength = 1.0;
+
+#if __IOS__ || __ANDROID__
+			/// <summary>
+			/// Sets a flag indicating whether <see cref="Windows.UI.Xaml.Controls.ListViewBase.ScrollIntoView(object)"/> will be animated smoothly or instant.
+			/// </summary>
+			/// <remarks>
+			/// Regardless of the value set, <see cref="Uno.UI.Helpers.ListViewHelper.InstantScrollToIndex(Windows.UI.Xaml.Controls.ListViewBase, int)"/>
+			/// and <see cref="Uno.UI.Helpers.ListViewHelper.SmoothScrollToIndex(Windows.UI.Xaml.Controls.ListViewBase, int)"/>
+			/// can be used to force a specific behavior.
+			/// </remarks>
+			public static bool AnimateScrollIntoView { get; set; } = true;
+#endif
 		}
 
 #if __ANDROID__

src/Uno.UI/Helpers/ListViewHelper.cs

@@ -10,16 +10,28 @@ public static partial class ListViewHelper
 		public static NativeListViewBase GetNativePanel(ListViewBase lvb) => lvb.NativePanel;
 
 #if __IOS__
-		public static void SmoothScroll(this ListViewBase lvb, int index, UIKit.UICollectionViewScrollPosition scrollPosition = UIKit.UICollectionViewScrollPosition.Top)
+		public static void InstantScrollToIndex(this ListViewBase lvb, int index, UIKit.UICollectionViewScrollPosition scrollPosition = UIKit.UICollectionViewScrollPosition.Top)
 		{
 			var indexPath = lvb.GetIndexPathFromIndex(index)?.ToNSIndexPath() ?? throw new IndexOutOfRangeException();
 
-			lvb.NativePanel.ScrollToItem(indexPath, scrollPosition, animated: true);
+			lvb.NativePanel?.ScrollToItem(indexPath, scrollPosition, animated: false);
+		}
+
+		public static void SmoothScrollToIndex(this ListViewBase lvb, int index, UIKit.UICollectionViewScrollPosition scrollPosition = UIKit.UICollectionViewScrollPosition.Top)
+		{
+			var indexPath = lvb.GetIndexPathFromIndex(index)?.ToNSIndexPath() ?? throw new IndexOutOfRangeException();
+
+			lvb.NativePanel?.ScrollToItem(indexPath, scrollPosition, animated: true);
 		}
 #elif __ANDROID__
-		public static void SmoothScroll(this ListViewBase lvb, int index)
+		public static void InstantScrollToIndex(this ListViewBase lvb, int index)
+		{
+			lvb.NativePanel?.ScrollToPosition(index);
+		}
+
+		public static void SmoothScrollToIndex(this ListViewBase lvb, int index)
 		{
-			lvb.NativePanel.SmoothScrollToPosition(index);
+			lvb.NativePanel?.SmoothScrollToPosition(index);
 		}
 #endif
 	}

src/Uno.UI/UI/Xaml/Controls/ListViewBase/Legacy/ListViewBase.Legacy.iOS.cs

@@ -73,7 +73,7 @@ public abstract partial class ListViewBase : BindableUICollectionView, IFramewor
 		/// <summary>
 		/// This property enables animations when using the ScrollIntoView Method.
 		/// </summary>
-		public bool AnimateScrollIntoView { get; set; } = false;
+		public bool AnimateScrollIntoView { get; set; } = Uno.UI.FeatureConfiguration.ListViewBase.AnimateScrollIntoView;
 		#endregion
 
 		#region Members

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

@@ -322,13 +322,19 @@ public void ScrollIntoView(object item, ScrollIntoViewAlignment alignment)
 			// occurring during scrolling are not always properly picked up by the layouting/rendering engine.
 			Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
 			{
-				var index = IndexFromItem(item);
-				if (index < 0)
+				if (IndexFromItem(item) is var index and >= 0)
 				{
-					return;
+					if (Uno.UI.FeatureConfiguration.ListViewBase.AnimateScrollIntoView)
+					{
+						NativePanel?.SmoothScrollToPosition(index);
+					}
+					else
+					{
+						var displayPosition = ConvertIndexToDisplayPosition(index);
+
+						NativePanel?.ScrollIntoView(displayPosition, alignment);
+					}
 				}
-				var displayPosition = ConvertIndexToDisplayPosition(index);
-				NativePanel?.ScrollIntoView(displayPosition, alignment);
 			});
 		}
 

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

@@ -27,7 +27,7 @@ public partial class ListViewBase
 		[Uno.UnoOnly]
 		public bool UseCollectionAnimations { get; set; } = true;
 
-		private bool _animateScrollIntoView;
+		private bool _animateScrollIntoView = Uno.UI.FeatureConfiguration.ListViewBase.AnimateScrollIntoView;
 		public bool AnimateScrollIntoView
 		{
 			get { return _animateScrollIntoView; }

src/Uno.UI/UI/Xaml/Controls/ListViewBase/NativeListViewBase.iOS.cs

@@ -65,7 +65,7 @@ public partial class NativeListViewBase : UICollectionView
 		/// <summary>
 		/// This property enables animations when using the ScrollIntoView Method.
 		/// </summary>
-		public bool AnimateScrollIntoView { get; set; } = false;
+		public bool AnimateScrollIntoView { get; set; } = Uno.UI.FeatureConfiguration.ListViewBase.AnimateScrollIntoView;
 		#endregion
 
 		#region Members