Port microsoft/microsoft-ui-xaml#4659

ModernWpf.Controls/NavigationView/NavigationView.cs

@@ -1790,6 +1790,8 @@ void OnSplitViewPaneClosing(DependencyObject sender, SplitViewPaneClosingEventAr
                             VisualStateManager.GoToState(this, "ListSizeCompact", true /*useTransitions*/);
                             UpdatePaneToggleSize();
                         }
+
+                        VisualStateManager.GoToState(this, "PaneNotOverlaying", true /*useTransitions*/);
                     }
                 }
             }
@@ -1806,6 +1808,14 @@ void OnSplitViewPaneOpening(DependencyObject sender, object obj)
             {
                 // See UpdateIsClosedCompact 'RS3+ animation timing enhancement' for explanation:
                 VisualStateManager.GoToState(this, "ListSizeFull", true /*useTransitions*/);
+
+                if (m_rootSplitView is { } splitView)
+                {
+                    if (splitView.DisplayMode == SplitViewDisplayMode.CompactOverlay || splitView.DisplayMode == SplitViewDisplayMode.Overlay)
+                    {
+                        VisualStateManager.GoToState(this, "PaneOverlaying", true /*useTransitions*/);
+                    }
+                }
             }
 
             PaneOpening?.Invoke(this, null);
@@ -4636,6 +4646,11 @@ void UpdateBackAndCloseButtonsVisibility()
 
             if (m_paneContentGrid is { } paneContentGridAsUIE)
             {
+                if (paneContentGridAsUIE is Border paneContentGridAsBorder)
+                {
+                    paneContentGridAsUIE = paneContentGridAsBorder.Child;
+                }
+
                 if (paneContentGridAsUIE is Grid paneContentGrid)
                 {
                     var rowDefs = paneContentGrid.RowDefinitions;

ModernWpf.Controls/SplitView/SplitView.cs

@@ -1,6 +1,5 @@
 using System.Diagnostics;
 using System.Windows;
-using System.Windows.Controls;
 using System.Windows.Input;
 using System.Windows.Markup;
 using System.Windows.Media;
@@ -10,7 +9,7 @@
 namespace ModernWpf.Controls
 {
     [ContentProperty(nameof(Content))]
-    public partial class SplitView : Control
+    public partial class SplitView : ControlEx
     {
         static SplitView()
         {

ModernWpf.Controls/SplitView/SplitView.xaml

@@ -11,11 +11,14 @@
     <GridLength x:Key="ZeroGridLength">0</GridLength>
 
     <Style TargetType="local:SplitView">
+        <Setter Property="BorderBrush" Value="{DynamicResource SystemControlForegroundTransparentBrush}" />
+        <Setter Property="BorderThickness" Value="{DynamicResource SplitViewLeftBorderThemeThickness}" />
         <Setter Property="HorizontalContentAlignment" Value="Stretch" />
         <Setter Property="VerticalContentAlignment" Value="Stretch" />
         <Setter Property="OpenPaneLength" Value="{DynamicResource SplitViewOpenPaneThemeLength}" />
         <Setter Property="CompactPaneLength" Value="{DynamicResource SplitViewCompactPaneThemeLength}" />
         <Setter Property="PaneBackground" Value="{DynamicResource SystemControlPageBackgroundChromeLowBrush}" />
+        <Setter Property="CornerRadius" Value="{DynamicResource SplitViewPaneRootCornerRadius}" />
         <Setter Property="Template">
             <Setter.Value>
                 <ControlTemplate TargetType="local:SplitView">
@@ -593,36 +596,45 @@
                             <ColumnDefinition x:Name="ColumnDefinition1" Width="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=TemplateSettings.OpenPaneGridLength, FallbackValue={StaticResource ZeroGridLength}}" />
                             <ColumnDefinition x:Name="ColumnDefinition2" Width="*" />
                         </Grid.ColumnDefinitions>
-                        <!-- Pane Content Area -->  
-                        <Grid
+
+                        <!-- Pane Content Area -->
+                        <Border
                             x:Name="PaneRoot"
                             Grid.ColumnSpan="2"
+                            BorderBrush="{TemplateBinding BorderBrush}"
+                            BorderThickness="{TemplateBinding BorderThickness}"
                             HorizontalAlignment="Left"
                             Visibility="Collapsed"
                             Background="{TemplateBinding PaneBackground}"
                             Width="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=TemplateSettings.OpenPaneLength}"
                             Canvas.ZIndex="1"
+                            CornerRadius="{TemplateBinding CornerRadius}"
                             KeyboardNavigation.TabNavigation="Local"
                             KeyboardNavigation.TabIndex="0">
-                            <Grid.Clip>
+                            <Border.Clip>
                                 <RectangleGeometry x:Name="PaneClipRectangle">
                                     <RectangleGeometry.Transform>
                                         <TranslateTransform x:Name="PaneClipRectangleTransform" />
                                     </RectangleGeometry.Transform>
                                 </RectangleGeometry>
-                            </Grid.Clip>
-                            <Grid.RenderTransform>
+                            </Border.Clip>
+
+                            <Border.RenderTransform>
                                 <TranslateTransform x:Name="PaneTransform" />
-                            </Grid.RenderTransform>
-                            <Border ui:BorderHelper.Child="{TemplateBinding Pane}" />
-                            <Rectangle
-                                x:Name="HCPaneBorder"
-                                Visibility="Collapsed"
-                                Fill="{DynamicResource SystemControlForegroundTransparentBrush}"
-                                Width="1"
-                                HorizontalAlignment="Right" />
+                            </Border.RenderTransform>
 
-                        </Grid>
+                            <Grid>
+                                <Border ui:BorderHelper.Child="{TemplateBinding Pane}" />
+
+                                <Rectangle
+                                    x:Name="HCPaneBorder"
+                                    Visibility="Collapsed"
+                                    Fill="{DynamicResource SystemControlForegroundTransparentBrush}"
+                                    Width="1"
+                                    HorizontalAlignment="Right" />
+                            </Grid>
+                        </Border>
+
                         <!-- Content Area -->
                         <Grid
                             x:Name="ContentRoot"
@@ -635,7 +647,6 @@
                                 x:Name="LightDismissLayer"
                                 Fill="Transparent"
                                 Visibility="Collapsed" />
-
                         </Grid>
 
                     </Grid>

ModernWpf/Controls/ControlEx.cs

@@ -0,0 +1,22 @@
+using System.Windows;
+using System.Windows.Controls;
+using ModernWpf.Controls.Primitives;
+
+namespace ModernWpf.Controls
+{
+    public class ControlEx : Control
+    {
+        #region CornerRadius
+
+        public static readonly DependencyProperty CornerRadiusProperty =
+            ControlHelper.CornerRadiusProperty.AddOwner(typeof(ControlEx));
+
+        public CornerRadius CornerRadius
+        {
+            get => (CornerRadius)GetValue(CornerRadiusProperty);
+            set => SetValue(CornerRadiusProperty, value);
+        }
+
+        #endregion
+    }
+}

ModernWpf/ControlsResources.xaml

@@ -81,6 +81,12 @@
     <Thickness x:Key="MenuFlyoutItemThemePadding">11,8,11,9</Thickness>
     <Thickness x:Key="MenuFlyoutItemThemePaddingNarrow">11,4,11,5</Thickness>
 
+    <sys:Double x:Key="SplitViewOpenPaneThemeLength">320</sys:Double>
+    <sys:Double x:Key="SplitViewCompactPaneThemeLength">48</sys:Double>
+    <Thickness x:Key="SplitViewLeftBorderThemeThickness">0,0,1,0</Thickness>
+    <Thickness x:Key="SplitViewRightBorderThemeThickness">1,0,0,0</Thickness>
+    <CornerRadius x:Key="SplitViewPaneRootCornerRadius">0</CornerRadius>
+
     <ControlTemplate x:Key="TextControlValidationErrorTemplate">
         <Grid SnapsToDevicePixels="True">
             <AdornedElementPlaceholder />

test/NavigationView_TestUI/Common/NavigationViewPage.xaml

@@ -318,7 +318,11 @@ Nullam egestas, orci sed molestie aliquet, diam ex euismod risus, ac dapibus qua
                     <Button x:Name="PaneFooterButton" AutomationProperties.Name="PaneFooterButton" Content="PaneFooter Button" Margin="8"/>
                     <muxcontrols:NavigationViewItem x:Name="PaneFooterNavigationViewItem"
                                                     AutomationProperties.Name="PaneFooterNavigationViewItem"
-                                                    Content="NVI" />
+                                                    Content="NVI">
+                        <muxcontrols:NavigationViewItem.Icon>
+                            <muxcontrols:SymbolIcon Symbol="Accept" />
+                        </muxcontrols:NavigationViewItem.Icon>
+                    </muxcontrols:NavigationViewItem>
                 </StackPanel>
             </muxcontrols:NavigationView.PaneFooter>
         </muxcontrols:NavigationView>