fix(scrollviewer): keyboard scrolling with arrow keys

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

@@ -72,6 +72,7 @@ partial void InitializePartial()
 
 			// Mouse wheel support
 			PointerWheelChanged += PointerWheelScroll;
+			KeyDown += KeyDownScroll;
 
 			// Touch scroll support
 			ManipulationMode = ManipulationModes.TranslateX | ManipulationModes.TranslateY; // Updated in PrepareTouchScroll!

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

@@ -3,6 +3,7 @@
 using Windows.Foundation;
 using Uno.UI;
 using Windows.System;
+using Windows.UI.Xaml.Input;
 #if __ANDROID__
 using View = Android.Views.View;
 using Font = Android.Graphics.Typeface;
@@ -272,6 +273,47 @@ private void PointerWheelScroll(object sender, Input.PointerRoutedEventArgs e)
 			}
 		}
 
+		private void KeyDownScroll(object sender, KeyRoutedEventArgs e)
+		{
+			var key = e.Key;
+			if (key != VirtualKey.Up && key != VirtualKey.Down && key != VirtualKey.Left && key != VirtualKey.Right)
+			{
+				return;
+			}
+
+			if (Content is UIElement)
+			{
+				var canScrollHorizontally = CanHorizontallyScroll;
+				var canScrollVertically = CanVerticallyScroll;
+				var delta = key is VirtualKey.Down or VirtualKey.Right ? -24 : 24;
+
+				if (canScrollHorizontally && (!canScrollVertically || key == VirtualKey.Left || key == VirtualKey.Right))
+				{
+#if __WASM__ // On wasm the scroll might be async (especially with disableAnimation: false), so we need to use the pending value to support high speed multiple wheel events
+					var horizontalOffset = _pendingScrollTo?.horizontal ?? HorizontalOffset;
+#else
+					var horizontalOffset = HorizontalOffset;
+#endif
+
+					Set(
+						horizontalOffset: horizontalOffset + delta,
+						disableAnimation: false);
+				}
+				else if (canScrollVertically && key is VirtualKey.Up or VirtualKey.Down)
+				{
+#if __WASM__ // On wasm the scroll might be async (especially with disableAnimation: false), so we need to use the pending value to support high speed multiple wheel events
+					var verticalOffset = _pendingScrollTo?.vertical ?? VerticalOffset;
+#else
+					var verticalOffset = VerticalOffset;
+#endif
+
+					Set(
+						verticalOffset: verticalOffset - delta,
+						disableAnimation: false);
+				}
+			}
+		}
+
 		public void SetVerticalOffset(double offset)
 			=> Set(verticalOffset: offset, disableAnimation: true);