更新

WPFDark/StandardControls/ScrollViewerEventHandler.cs

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+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Input;
+using WPFDark.Internals;
+
+
+namespace WPFDark.StandardControls
+{
+    public partial class ScrollViewerEventHandler
+    {
+        private const double Response = 150.0;
+        private const double MaxOpacity = 0.6;
+        private const double BarWidth = 8.0;
+
+        private void OnPreviewMouseMove(object sender, MouseEventArgs e)
+        {
+            var self = ((FrameworkElement) sender).GetParent<ScrollViewer>();
+            
+            if (self is null)
+                return;
+
+            var pos = e.GetPosition(self);
+            var posX = pos.X;
+            var posY = pos.Y;
+
+            var width = (1.0, self.ActualWidth - BarWidth).Max();
+            var height = (1.0, self.ActualHeight - BarWidth).Max();
+
+            if (ScrollViewerAttachedProperties.GetIsLeftVerticalScrollBar(self))
+                posX = width - posX;
+
+            var xr = (Response, width).Min();
+            var yr = (Response, height).Min();
+
+            var xir = width - xr;
+            var yir = height - yr;
+
+            var xd = NumberHelper.Clamp01((posX - xir) / xr);
+            var yd = NumberHelper.Clamp01((posY - yir) / yr);
+
+            var xo = xd * MaxOpacity;
+            var yo = yd * MaxOpacity;
+
+            ScrollViewerAttachedProperties.SetVerticalScrollBarOpacity(self, xo);
+            ScrollViewerAttachedProperties.SetHorizontalScrollBarOpacity(self, yo);
+        }
+
+        private void OnMouseLeave(object sender, MouseEventArgs e)
+        {
+            var self = ((FrameworkElement) sender).GetParent<ScrollViewer>();
+
+            if (self is null)
+                return;
+
+            ScrollViewerAttachedProperties.SetVerticalScrollBarOpacity(self, 0.0);
+            ScrollViewerAttachedProperties.SetHorizontalScrollBarOpacity(self, 0.0);
+        }
+    }
+}