From a5ec556f0d8516f03f670de2494ed5fff5be76a7 Mon Sep 17 00:00:00 2001
From: David <github.site@torick.net>
Date: Thu, 6 May 2021 15:52:07 -0400
Subject: [PATCH] feat(scrollviewer): Add ability to configure scrollbar's
 auto-hide delay, and fully disable auto-hide

---
 src/Uno.UI/FeatureConfiguration.cs            |  8 +++++
 .../Controls/ScrollViewer/ScrollViewer.cs     | 36 +++++++++++++++----
 2 files changed, 38 insertions(+), 6 deletions(-)

diff --git a/src/Uno.UI/FeatureConfiguration.cs b/src/Uno.UI/FeatureConfiguration.cs
index 299c7fdb6d14..cdbd6dc4f91f 100644
--- a/src/Uno.UI/FeatureConfiguration.cs
+++ b/src/Uno.UI/FeatureConfiguration.cs
@@ -395,6 +395,14 @@ public static class ScrollViewer
 			/// </remarks>
 			public static ScrollViewerUpdatesMode DefaultUpdatesMode { get; set; } = ScrollViewerUpdatesMode.AsynchronousIdle;
 
+			/// <summary>
+			/// Defines the delay after which the scrollbars hide themselves when pointer is not over.<br/>
+			/// Default is 4 sec.<br/>
+			/// Setting this to <see cref="TimeSpan.MaxValue"/> will completely disable the auto hide feature.
+			/// </summary>
+			/// <remarks>This is effective only for managed scrollbars (WASM, macOS and Skia for now)</remarks>
+			public static TimeSpan? DefaultAutoHideDelay { get; set; }
+
 #if __ANDROID__
 			/// <summary>
 			/// This value defines an optional delay to be set for native ScrollBar thumbs to disapear. The
diff --git a/src/Uno.UI/UI/Xaml/Controls/ScrollViewer/ScrollViewer.cs b/src/Uno.UI/UI/Xaml/Controls/ScrollViewer/ScrollViewer.cs
index f57fae020379..6d4bff1b7c93 100644
--- a/src/Uno.UI/UI/Xaml/Controls/ScrollViewer/ScrollViewer.cs
+++ b/src/Uno.UI/UI/Xaml/Controls/ScrollViewer/ScrollViewer.cs
@@ -907,7 +907,7 @@ protected override void OnApplyTemplate()
 
 			OnBringIntoViewOnFocusChangeChangedPartial(BringIntoViewOnFocusChange);
 
-			ResetScrollIndicator(forced: true);
+			PrepareScrollIndicator();
 		}
 
 		partial void OnApplyTemplatePartial();
@@ -1368,16 +1368,30 @@ public bool ChangeView(double? horizontalOffset, double? verticalOffset, float?
 			return ChangeViewNative(horizontalOffset, verticalOffset, zoomFactor, disableAnimation);
 		}
 
-#region Scroll indicators visual states (Managed scroll bars only)
+		#region Scroll indicators visual states (Managed scroll bars only)
+		private static readonly TimeSpan _indicatorResetDelay = FeatureConfiguration.ScrollViewer.DefaultAutoHideDelay ?? TimeSpan.FromSeconds(4);
+		private static readonly bool _indicatorResetDisabled = _indicatorResetDelay == TimeSpan.MaxValue;
 		private DispatcherQueueTimer? _indicatorResetTimer;
 		private string? _indicatorState;
 
+		private void PrepareScrollIndicator() // OnApplyTemplate
+		{
+			if (_indicatorResetDisabled)
+			{
+				ShowScrollIndicator(PointerDeviceType.Mouse, forced: true);
+			}
+			else
+			{
+				ResetScrollIndicator(forced: true);
+			}
+		}
+
 		private static void ShowScrollIndicator(object sender, PointerRoutedEventArgs e) // OnPointerMove
 			=> (sender as ScrollViewer)?.ShowScrollIndicator(e.Pointer.PointerDeviceType);
 
-		private void ShowScrollIndicator(PointerDeviceType type)
+		private void ShowScrollIndicator(PointerDeviceType type, bool forced = false)
 		{
-			if (!ComputedIsVerticalScrollEnabled && !ComputedIsHorizontalScrollEnabled)
+			if (!forced && !ComputedIsVerticalScrollEnabled && !ComputedIsHorizontalScrollEnabled)
 			{
 				return;
 			}
@@ -1393,13 +1407,18 @@ private void ShowScrollIndicator(PointerDeviceType type)
 				_indicatorState = indicatorState;
 			}
 
+			if (_indicatorResetDisabled)
+			{
+				return;
+			}
+
 			// Automatically hide the scroll indicator after a delay without any interaction
 			if (_indicatorResetTimer == null)
 			{
 				var weakRef = WeakReferencePool.RentSelfWeakReference(this);
 				_indicatorResetTimer = new DispatcherQueueTimer
 				{
-					Interval = TimeSpan.FromSeconds(4),
+					Interval = _indicatorResetDelay,
 					IsRepeating = false
 				};
 				_indicatorResetTimer.Tick += (snd, e) => (weakRef.Target as ScrollViewer)?.ResetScrollIndicator();
@@ -1412,6 +1431,11 @@ private void ShowScrollIndicator(PointerDeviceType type)
 
 		private void ResetScrollIndicator(bool forced = false)
 		{
+			if (_indicatorResetDisabled)
+			{
+				return;
+			}
+
 			_indicatorResetTimer?.Stop();
 
 			if (!forced && ((_horizontalScrollbar?.IsPointerOver ?? false) || (_verticalScrollbar?.IsPointerOver ?? false)))
@@ -1447,6 +1471,6 @@ private void ResetScrollIndicator(bool forced = false)
 				VisualStateManager.GoToState(this, VisualStates.ScrollBarsSeparator.Collapsed, true);
 			}
 		}
-#endregion
+		#endregion
 	}
 }