support for sync with system theme

src/Shared/HandyControl_Shared/Controls/Attach/DataGridAttach.cs

@@ -337,7 +337,7 @@ namespace HandyControl.Controls
         }
 
         public static void SetCanUnselectAllWithBlankArea(DependencyObject element, bool value)
-            => element.SetValue(CanUnselectAllWithBlankAreaProperty, value);
+            => element.SetValue(CanUnselectAllWithBlankAreaProperty, ValueBoxes.BooleanBox(value));
 
         public static bool GetCanUnselectAllWithBlankArea(DependencyObject element)
             => (bool) element.GetValue(CanUnselectAllWithBlankAreaProperty);

src/Shared/HandyControl_Shared/Controls/Attach/DropDownElement.cs

@@ -20,7 +20,7 @@ namespace HandyControl.Controls
             new FrameworkPropertyMetadata(ValueBoxes.FalseBox, FrameworkPropertyMetadataOptions.Inherits));
 
         public static void SetAutoWidth(DependencyObject element, bool value)
-            => element.SetValue(AutoWidthProperty, value);
+            => element.SetValue(AutoWidthProperty, ValueBoxes.BooleanBox(value));
 
         public static bool GetAutoWidth(DependencyObject element)
             => (bool) element.GetValue(AutoWidthProperty);

src/Shared/HandyControl_Shared/Controls/Attach/WindowAttach.cs

@@ -141,7 +141,7 @@ namespace HandyControl.Controls
         }
 
         public static void SetHideWhenClosing(DependencyObject element, bool value)
-            => element.SetValue(HideWhenClosingProperty, value);
+            => element.SetValue(HideWhenClosingProperty, ValueBoxes.BooleanBox(value));
 
         public static bool GetHideWhenClosing(DependencyObject element)
             => (bool) element.GetValue(HideWhenClosingProperty);