Fix theme change

samples/DockReactiveUICanonicalSample/App.axaml

@@ -22,8 +22,9 @@
       </Styles.Resources>
     </Styles>
     <Style Selector="HostWindow">
-      <Setter Property="Content">
-        <Template>
+      <Setter Property="Content" Value="{Binding}" />
+      <Setter Property="ContentTemplate">
+        <DataTemplate>
           <Panel Margin="{Binding $parent[HostWindow].OffScreenMargin}">
             <Panel Margin="{Binding $parent[HostWindow].WindowDecorationMargin}">
               <OverlayHost VisualTreeLifecycleBehavior.IsEnabled="True">
@@ -36,12 +37,13 @@
               </OverlayHost>
             </Panel>
           </Panel>
-        </Template>
+        </DataTemplate>
       </Setter>
     </Style>
     <Style Selector="HostWindow:toolwindow">
-      <Setter Property="Content">
-        <Template>
+      <Setter Property="Content" Value="{Binding}" />
+      <Setter Property="ContentTemplate">
+        <DataTemplate>
           <Panel Margin="{Binding $parent[HostWindow].OffScreenMargin}">
             <OverlayHost VisualTreeLifecycleBehavior.IsEnabled="True">
               <DockControl Layout="{Binding}"
@@ -52,7 +54,7 @@
               </DockControl>
             </OverlayHost>
           </Panel>
-        </Template>
+        </DataTemplate>
       </Setter>
     </Style>
     <Style Selector="HostWindow:toolchromecontrolswindow">

src/Dock.Avalonia.Themes.Fluent/Controls/HostWindow.axaml

@@ -51,16 +51,17 @@
       </ControlTemplate>
     </Setter>
 
-    <Setter Property="Content">
-      <Template>
+    <Setter Property="Content" Value="{Binding}" />
+    <Setter Property="ContentTemplate">
+      <DataTemplate>
         <Panel Margin="{Binding $parent[HostWindow].OffScreenMargin}">
           <Panel Margin="{Binding $parent[HostWindow].WindowDecorationMargin}">
             <OverlayHost VisualTreeLifecycleBehavior.IsEnabled="True">
               <DockControl Layout="{Binding}" />
             </OverlayHost>
           </Panel>
         </Panel>
-      </Template>
+      </DataTemplate>
     </Setter>
 
     <Style Selector="^:documentwindow">
@@ -104,14 +105,15 @@
         </ControlTemplate>
       </Setter>
 
-      <Setter Property="Content">
-        <Template>
+      <Setter Property="Content" Value="{Binding}" />
+      <Setter Property="ContentTemplate">
+        <DataTemplate>
           <Panel Margin="{Binding $parent[HostWindow].OffScreenMargin}">
             <OverlayHost VisualTreeLifecycleBehavior.IsEnabled="True">
               <DockControl Layout="{Binding}" />
             </OverlayHost>
           </Panel>
-        </Template>
+        </DataTemplate>
       </Setter>
 
     </Style>

src/Dock.Avalonia/Controls/Overlays/OverlayHost.cs

@@ -250,6 +250,14 @@ private void OnOverlayLayerPropertyChanged(object? sender, AvaloniaPropertyChang
 
     private void RebuildPipeline()
     {
+        if (Content is Control hostedContent && hostedContent.Parent is not null)
+        {
+            if (!TryDetachControl(hostedContent))
+            {
+                return;
+            }
+        }
+
         Child = null;
 
         var contentPresenter = new ContentPresenter
@@ -268,7 +276,7 @@ private void RebuildPipeline()
                 continue;
             }
 
-            if (!TryDetachOverlay(overlay))
+            if (!TryDetachControl(overlay))
             {
                 continue;
             }
@@ -315,25 +323,25 @@ private void RebuildPipeline()
         Child = current;
     }
 
-    private static bool TryDetachOverlay(Control overlay)
+    private static bool TryDetachControl(Control control)
     {
-        if (overlay.Parent is null)
+        if (control.Parent is null)
         {
             return true;
         }
 
-        switch (overlay.Parent)
+        switch (control.Parent)
         {
             case Panel panel:
-                panel.Children.Remove(overlay);
+                panel.Children.Remove(control);
                 return true;
-            case Decorator decorator when ReferenceEquals(decorator.Child, overlay):
+            case Decorator decorator when ReferenceEquals(decorator.Child, control):
                 decorator.Child = null;
                 return true;
-            case ContentPresenter presenter when ReferenceEquals(presenter.Content, overlay):
+            case ContentPresenter presenter when ReferenceEquals(presenter.Content, control):
                 presenter.Content = null;
                 return true;
-            case ContentControl contentControl when ReferenceEquals(contentControl.Content, overlay):
+            case ContentControl contentControl when ReferenceEquals(contentControl.Content, control):
                 contentControl.Content = null;
                 return true;
             default:

tests/Dock.Avalonia.HeadlessTests/HostWindowThemeChangeTests.cs

@@ -0,0 +1,55 @@
+using System;
+using Avalonia;
+using Avalonia.Headless.XUnit;
+using Avalonia.Styling;
+using Dock.Avalonia.Controls;
+using Dock.Model.Avalonia;
+using Dock.Model.Controls;
+using Dock.Model.Core;
+using Xunit;
+
+namespace Dock.Avalonia.HeadlessTests;
+
+public class HostWindowThemeChangeTests
+{
+    private static IRootDock CreateLayout(Factory factory)
+    {
+        var root = factory.CreateRootDock();
+        root.Factory = factory;
+        root.VisibleDockables = factory.CreateList<IDockable>();
+        return root;
+    }
+
+    [AvaloniaFact]
+    public void HostWindow_ThemeChange_DoesNotDuplicate_DockControls()
+    {
+        var app = Application.Current ?? throw new InvalidOperationException("Application is not initialized.");
+        var factory = new Factory();
+        var layout = CreateLayout(factory);
+        var window = new HostWindow();
+        var originalVariant = app.RequestedThemeVariant;
+
+        try
+        {
+            window.SetLayout(layout);
+            window.Show();
+            window.UpdateLayout();
+
+            Assert.Single(factory.DockControls);
+            Assert.Same(layout, window.Content);
+
+            app.RequestedThemeVariant = ThemeVariant.Dark;
+            window.UpdateLayout();
+            Assert.Single(factory.DockControls);
+
+            app.RequestedThemeVariant = ThemeVariant.Light;
+            window.UpdateLayout();
+            Assert.Single(factory.DockControls);
+        }
+        finally
+        {
+            window.Close();
+            app.RequestedThemeVariant = originalVariant;
+        }
+    }
+}