Allow setting ThemeVariant to Default to reset theme to system on android (#16340)

* allow setting ThemeVariant to Default to reset theme to system on android

* update api diff

* Fix theme variant not being applied when switching from Light/Dark to Default

* Use IPlatformSettings as a fallback in macOS SetFrameThemeVariant

* fix nullable check in android avaloniaview

* fix SetFrameThemeVariant api suppression

* fix accessibility helper crash

* fix reseting actual theme variant

* rebased

* update apidiff

* update apidiff

* fix default theme selection on desktop

* add missing changes

* fix wayland default theme detection

* fix browser theme detection

* removed redundant overrides

* Fix macOS default theme detection

* Fix iOS default theme detection

* Avoid async void

---------

Co-authored-by: Max Katz <maxkatz6@outlook.com>
Co-authored-by: Julien Lebosquain <julien@lebosquain.net>

api/Avalonia.nupkg.xml

@@ -43,6 +43,18 @@
     <Left>baseline/Avalonia/lib/net10.0/Avalonia.Base.dll</Left>
     <Right>current/Avalonia/lib/net10.0/Avalonia.Base.dll</Right>
   </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0002</DiagnosticId>
+    <Target>M:Avalonia.Controls.Embedding.Offscreen.OffscreenTopLevelImplBase.SetFrameThemeVariant(Avalonia.Platform.PlatformThemeVariant)</Target>
+    <Left>baseline/Avalonia/lib/net10.0/Avalonia.Controls.dll</Left>
+    <Right>current/Avalonia/lib/net10.0/Avalonia.Controls.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0002</DiagnosticId>
+    <Target>M:Avalonia.Platform.ITopLevelImpl.SetFrameThemeVariant(Avalonia.Platform.PlatformThemeVariant)</Target>
+    <Left>baseline/Avalonia/lib/net10.0/Avalonia.Controls.dll</Left>
+    <Right>current/Avalonia/lib/net10.0/Avalonia.Controls.dll</Right>
+  </Suppression>
   <Suppression>
     <DiagnosticId>CP0002</DiagnosticId>
     <Target>M:Avalonia.OpenGL.Egl.EglPlatformSurfaceRenderTargetBase.BeginDraw(Avalonia.OpenGL.Egl.EglSurface,Avalonia.PixelSize,System.Double,System.Action,System.Boolean)</Target>
@@ -91,6 +103,18 @@
     <Left>baseline/Avalonia/lib/net8.0/Avalonia.Base.dll</Left>
     <Right>current/Avalonia/lib/net8.0/Avalonia.Base.dll</Right>
   </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0002</DiagnosticId>
+    <Target>M:Avalonia.Controls.Embedding.Offscreen.OffscreenTopLevelImplBase.SetFrameThemeVariant(Avalonia.Platform.PlatformThemeVariant)</Target>
+    <Left>baseline/Avalonia/lib/net8.0/Avalonia.Controls.dll</Left>
+    <Right>current/Avalonia/lib/net8.0/Avalonia.Controls.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0002</DiagnosticId>
+    <Target>M:Avalonia.Platform.ITopLevelImpl.SetFrameThemeVariant(Avalonia.Platform.PlatformThemeVariant)</Target>
+    <Left>baseline/Avalonia/lib/net8.0/Avalonia.Controls.dll</Left>
+    <Right>current/Avalonia/lib/net8.0/Avalonia.Controls.dll</Right>
+  </Suppression>
   <Suppression>
     <DiagnosticId>CP0002</DiagnosticId>
     <Target>M:Avalonia.OpenGL.Egl.EglPlatformSurfaceRenderTargetBase.BeginDraw(Avalonia.OpenGL.Egl.EglSurface,Avalonia.PixelSize,System.Double,System.Action,System.Boolean)</Target>
@@ -103,10 +127,22 @@
     <Left>baseline/Avalonia/lib/net10.0/Avalonia.Controls.dll</Left>
     <Right>current/Avalonia/lib/net10.0/Avalonia.Controls.dll</Right>
   </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0006</DiagnosticId>
+    <Target>M:Avalonia.Platform.ITopLevelImpl.SetFrameThemeVariant(System.Nullable{Avalonia.Platform.PlatformThemeVariant})</Target>
+    <Left>baseline/Avalonia/lib/net10.0/Avalonia.Controls.dll</Left>
+    <Right>current/Avalonia/lib/net10.0/Avalonia.Controls.dll</Right>
+  </Suppression>
   <Suppression>
     <DiagnosticId>CP0006</DiagnosticId>
     <Target>M:Avalonia.Controls.Platform.IWin32OptionsTopLevelImpl.SetWindowCornerPreference(Avalonia.Controls.Win32Properties.WindowCornerPreference)</Target>
     <Left>baseline/Avalonia/lib/net8.0/Avalonia.Controls.dll</Left>
     <Right>current/Avalonia/lib/net8.0/Avalonia.Controls.dll</Right>
   </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0006</DiagnosticId>
+    <Target>M:Avalonia.Platform.ITopLevelImpl.SetFrameThemeVariant(System.Nullable{Avalonia.Platform.PlatformThemeVariant})</Target>
+    <Left>baseline/Avalonia/lib/net8.0/Avalonia.Controls.dll</Left>
+    <Right>current/Avalonia/lib/net8.0/Avalonia.Controls.dll</Right>
+  </Suppression>
 </Suppressions>

samples/SafeAreaDemo/App.xaml

@@ -2,7 +2,7 @@
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              xmlns:local="using:SafeAreaDemo"
              x:Class="SafeAreaDemo.App"
-             RequestedThemeVariant="Light">
+             RequestedThemeVariant="Default">
     <Application.DataTemplates>
         <local:ViewLocator/>
     </Application.DataTemplates>

samples/SafeAreaDemo/ViewModels/MainViewModel.cs

@@ -3,6 +3,7 @@ using Avalonia;
 using Avalonia.Animation.Easings;
 using Avalonia.Controls;
 using Avalonia.Controls.Platform;
+using Avalonia.Styling;
 using MiniMvvm;
 
 namespace SafeAreaDemo.ViewModels
@@ -33,7 +34,7 @@ namespace SafeAreaDemo.ViewModels
         public Rect InputPaneRect => _inputPane?.OccludedRect ?? default;
 
         public Rect CanvasSize { get; set; }
-        
+
         public Thickness SafeAreaPadding
         {
             get
@@ -105,7 +106,7 @@ namespace SafeAreaDemo.ViewModels
             set
             {
                 _autoSafeAreaPadding = value;
-                
+
                 RaisePropertyChanged();
                 RaiseSafeAreaChanged();
             }
@@ -159,7 +160,7 @@ namespace SafeAreaDemo.ViewModels
             this.RaisePropertyChanged(nameof(ViewPadding));
             this.RaisePropertyChanged(nameof(InputPaneMarkerMargin));
         }
-        
+
         private void RaiseKeyboardChanged()
         {
             this.RaisePropertyChanged(nameof(InputPaneState));
@@ -168,5 +169,29 @@ namespace SafeAreaDemo.ViewModels
             this.RaisePropertyChanged(nameof(InputPaneDuration));
             this.RaisePropertyChanged(nameof(InputPaneMarkerMargin));
         }
+
+        public void SetLight()
+        {
+            if (Application.Current is { } application)
+            {
+                application.RequestedThemeVariant = ThemeVariant.Light;
+            }
+        }
+
+        public void SetDark()
+        {
+            if (Application.Current is { } application)
+            {
+                application.RequestedThemeVariant = ThemeVariant.Dark;
+            }
+        }
+
+        public void SetDefault()
+        {
+            if (Application.Current is { } application)
+            {
+                application.RequestedThemeVariant = ThemeVariant.Default;
+            }
+        }
     }
 }

samples/SafeAreaDemo/Views/MainView.xaml

@@ -8,7 +8,6 @@
              d:DesignHeight="450"
              x:Class="SafeAreaDemo.Views.MainView"
              x:DataType="vm:MainViewModel"
-             Background="#ccc"
              TopLevel.AutoSafeAreaPadding="{Binding AutoSafeAreaPadding, Mode=TwoWay}">
     <Grid HorizontalAlignment="Stretch"
           VerticalAlignment="Stretch"
@@ -40,6 +39,7 @@
                       HorizontalAlignment="Stretch"
                       VerticalAlignment="Stretch">
                     <StackPanel Orientation="Vertical"
+                                Spacing="5"
                                 HorizontalAlignment="Center"
                                 VerticalAlignment="Center">
                         <Label HorizontalAlignment="Left">Options:</Label>
@@ -47,7 +47,12 @@
                         <CheckBox IsChecked="{Binding UseSafeArea}" IsEnabled="{Binding !AutoSafeAreaPadding}">Use Safe Area</CheckBox>
                         <CheckBox IsChecked="{Binding AutoSafeAreaPadding}">Automatic Paddings</CheckBox>
                         <CheckBox IsChecked="{Binding HideSystemBars}">Hide System Bars</CheckBox>
-                         <TextBox Width="200" PlaceholderText="Tap to Show Keyboard"/>
+                        <TextBox Width="200" PlaceholderText="Tap to Show Keyboard"/>
+                        <StackPanel Orientation="Horizontal" Spacing="10">
+                          <Button Command="{Binding SetLight}">Light</Button>
+                          <Button Command="{Binding SetDark}">Dark</Button>
+                          <Button Command="{Binding SetDefault}">Default</Button>
+                        </StackPanel>
                     </StackPanel>
                 </Grid>
             </DockPanel>

src/Android/Avalonia.Android/AvaloniaView.Input.cs

@@ -22,14 +22,14 @@ namespace Avalonia.Android
         protected override void OnFocusChanged(bool gainFocus, FocusSearchDirection direction, global::Android.Graphics.Rect? previouslyFocusedRect)
         {
             base.OnFocusChanged(gainFocus, direction, previouslyFocusedRect);
-            _accessHelper.OnFocusChanged(gainFocus, (int)direction, previouslyFocusedRect);
+            _accessHelper?.OnFocusChanged(gainFocus, (int)direction, previouslyFocusedRect);
         }
 
         protected override bool DispatchHoverEvent(MotionEvent? e)
         {
             var res = _view.PointerHelper.DispatchMotionEvent(e, out var callBase);
             if (res == false)
-                callBase = !_accessHelper.DispatchHoverEvent(e!) && callBase;
+                callBase = (_accessHelper?.DispatchHoverEvent(e!) == true) && callBase;
 
             var baseResult = callBase && base.DispatchHoverEvent(e);
 
@@ -63,7 +63,7 @@ namespace Avalonia.Android
         {
             var res = _view.KeyboardHelper.DispatchKeyEvent(e, out var callBase);
             if (res == false)
-                callBase = !_accessHelper.DispatchKeyEvent(e!) && callBase;
+                callBase = _accessHelper?.DispatchKeyEvent(e!) == false && callBase;
 
             var baseResult = callBase && base.DispatchKeyEvent(e);
 

src/Android/Avalonia.Android/AvaloniaView.cs

@@ -19,11 +19,13 @@ namespace Avalonia.Android
 {
     public partial class AvaloniaView : FrameLayout
     {
-        private EmbeddableControlRoot _root;
+        private EmbeddableControlRoot? _root;
+        private ExploreByTouchHelper? _accessHelper;
+
         private readonly ViewImpl _view;
-        private readonly ExploreByTouchHelper _accessHelper;
 
         private IDisposable? _timerSubscription;
+        private object? _content;
         private bool _surfaceCreated;
 
         public AvaloniaView(Context context) : base(context)
@@ -32,11 +34,13 @@ namespace Avalonia.Android
 
             AddView(_view.View);
 
+            this.SetBackgroundColor(global::Android.Graphics.Color.Transparent);
+
             _root = new EmbeddableControlRoot(_view);
             _root.Prepare();
 
             SetBackgroundColor(global::Android.Graphics.Color.Transparent);
-            OnConfigurationChanged();
+            OnConfigurationChanged(null);
 
             _view.InternalView!.SurfaceWindowCreated += InternalView_SurfaceWindowCreated;
             _view.InternalView.SurfaceWindowDestroyed += InternalView_SurfaceWindowDestroyed;
@@ -69,16 +73,50 @@ namespace Avalonia.Android
 
         public object? Content
         {
-            get { return _root.Content; }
-            set { _root.Content = value; }
+            get { return _root?.Content; }
+            set
+            {
+                _content = value;
+                if (_root != null)
+                    _root.Content = value;
+            }
         }
 
         internal new void Dispose()
         {
+            _root?.Dispose();
+            _root = null;
+            _content = null;
+        }
+
+        protected override void OnDetachedFromWindow()
+        {
+            base.OnDetachedFromWindow();
             OnVisibilityChanged(false);
             _surfaceCreated = false;
-            _root?.Dispose();
-            _root = null!;
+
+            if (_accessHelper is { } accessHelper)
+            {
+                ViewCompat.SetAccessibilityDelegate(this, null);
+                _accessHelper = null;
+            }
+        }
+
+        protected override void OnAttachedToWindow()
+        {
+            _root?.Content = null;
+            _root = new EmbeddableControlRoot(_view);
+            _root.Prepare();
+            if (_content != null)
+            {
+                _root.Content = _content;
+            }
+
+            _accessHelper = new AvaloniaAccessHelper(this);
+            ViewCompat.SetAccessibilityDelegate(this, _accessHelper);
+            SendConfigurationChanged(Context?.Resources?.Configuration);
+
+            base.OnAttachedToWindow();
         }
 
         [SupportedOSPlatform("android24.0")]
@@ -98,6 +136,7 @@ namespace Avalonia.Android
         {
             if (_root == null || !_surfaceCreated)
                 return;
+
             if (isVisible && _timerSubscription == null)
             {
                 if (AndroidPlatform.Timer is { } timer)
@@ -119,20 +158,21 @@ namespace Avalonia.Android
                 _timerSubscription = null;
             }
         }
-        
+
         protected override void OnConfigurationChanged(Configuration? newConfig)
         {
             base.OnConfigurationChanged(newConfig);
-            OnConfigurationChanged();
+            SendConfigurationChanged(newConfig ?? Context?.Resources?.Configuration);
         }
 
-        private void OnConfigurationChanged()
+        private void SendConfigurationChanged(Configuration? newConfig)
         {
-            if (Context is { } context)
+            _view.InsetsManager?.SetDefaultSystemLightMode(!(newConfig?.UiMode.HasFlag(UiMode.NightYes) ?? false));
+            if (Context is { } context && newConfig is { } config)
             {
                 var settings =
                     AvaloniaLocator.Current.GetRequiredService<IPlatformSettings>() as AndroidPlatformSettings;
-                settings?.OnViewConfigurationChanged(context);
+                settings?.OnViewConfigurationChanged(context, config);
                 ((AndroidScreens)_view.TryGetFeature<IScreenImpl>()!).OnChanged();
             }
         }
@@ -146,7 +186,7 @@ namespace Avalonia.Android
 
             private void ViewImpl_FocusChange(object? sender, FocusChangeEventArgs e)
             {
-                if(!e.HasFocus)
+                if (!e.HasFocus)
                     LostFocus?.Invoke();
             }
         }

src/Android/Avalonia.Android/Platform/AndroidInsetsManager.cs

@@ -187,6 +187,11 @@ namespace Avalonia.Android.Platform
             return insets;
         }
 
+        internal void SetDefaultSystemLightMode(bool islightMode)
+        {
+            _isDefaultSystemBarLightTheme = islightMode;
+        }
+
         private void NotifySafeAreaChanged(Thickness safeAreaPadding)
         {
             Dispatcher.UIThread.Send(_ => SafeAreaChanged?.Invoke(this, new SafeAreaChangedArgs(safeAreaPadding)));

src/Android/Avalonia.Android/Platform/AndroidPlatformSettings.cs

@@ -49,14 +49,14 @@ internal class AndroidPlatformSettings : DefaultPlatformSettings
 
     public override TimeSpan HoldWaitDuration => _holdWaitDuration;
 
-    internal void OnViewConfigurationChanged(Context context)
+    internal void OnViewConfigurationChanged(Context context, Configuration configuration)
     {
-        if (context.Resources?.Configuration is null)
+        if (context.Resources is null)
         {
             return;
         }
 
-        var systemTheme = (context.Resources.Configuration.UiMode & UiMode.NightMask) switch
+        PlatformThemeVariant systemTheme = (configuration.UiMode & UiMode.NightMask) switch
         {
             UiMode.NightYes => PlatformThemeVariant.Dark,
             UiMode.NightNo => PlatformThemeVariant.Light,
@@ -98,7 +98,7 @@ internal class AndroidPlatformSettings : DefaultPlatformSettings
                 }
                 finally
                 {
-                    array.Recycle();   
+                    array.Recycle();
                 }
             }
         }

src/Android/Avalonia.Android/Platform/SkiaPlatform/TopLevelImpl.cs

@@ -8,6 +8,7 @@ using Android.OS;
 using Android.Runtime;
 using Android.Views;
 using AndroidX.AppCompat.App;
+using AndroidX.Core.View;
 using Avalonia.Android.Platform.Input;
 using Avalonia.Android.Platform.Specific.Helpers;
 using Avalonia.Android.Platform.Storage;
@@ -232,7 +233,7 @@ namespace Avalonia.Android.Platform.SkiaPlatform
             }
         }
 
-        public void SetFrameThemeVariant(PlatformThemeVariant themeVariant)
+        public void SetFrameThemeVariant(PlatformThemeVariant? themeVariant)
         {
             if (_insetsManager != null)
             {
@@ -244,7 +245,23 @@ namespace Avalonia.Android.Platform.SkiaPlatform
                 };
             }
 
-            AppCompatDelegate.DefaultNightMode = themeVariant == PlatformThemeVariant.Light ? AppCompatDelegate.ModeNightNo : AppCompatDelegate.ModeNightYes;
+            // Sets the default app NightMode to AppCompatDelegate.ModeNightFollowSystem when themeVariant is null. This
+            // allows app to follow the current OS night mode. Using either ModeNightNo or ModeNightYes will force the app
+            // to use one night mode, ignoring the system's configuration and preventing us from detecting system theme changes
+            // in View.OnConfigurationChanged. In this case, only Activity.OnConfigurationChanged is called when system theme is
+            // changed, but we don't have access to that method if the toplevel view is embedded in a custom activity
+            var nightMode = themeVariant == null ? AppCompatDelegate.ModeNightFollowSystem :
+                themeVariant == PlatformThemeVariant.Light ? AppCompatDelegate.ModeNightNo : AppCompatDelegate.ModeNightYes;
+
+            AppCompatDelegate.DefaultNightMode = nightMode;
+
+            if (nightMode == AppCompatDelegate.ModeNightFollowSystem && _view?.Context is { } context
+                && context.Resources?.Configuration is { } config)
+            {
+                var settings =
+                    AvaloniaLocator.Current.GetRequiredService<IPlatformSettings>() as AndroidPlatformSettings;
+                settings?.OnViewConfigurationChanged(context, config);
+            }
         }
 
         public AcrylicPlatformCompensationLevels AcrylicCompensationLevels => new(1, 1, 1);
@@ -254,8 +271,8 @@ namespace Avalonia.Android.Platform.SkiaPlatform
         PixelSize EglGlPlatformSurface.IEglWindowGlPlatformSurfaceInfo.Size => _view?.Size ?? default;
         double EglGlPlatformSurface.IEglWindowGlPlatformSurfaceInfo.Scaling => _view?.Scaling ?? default;
 
+        internal AndroidInsetsManager? InsetsManager => _insetsManager;
         internal AndroidKeyboardEventsHelper<TopLevelImpl> KeyboardHelper => _keyboardHelper;
-
         internal AndroidMotionEventsHelper PointerHelper => _pointerHelper;
 
         public void SetTransparencyLevelHint(IReadOnlyList<WindowTransparencyLevel> transparencyLevels)

src/Avalonia.Base/Styling/ThemeVariant.cs

@@ -100,11 +100,11 @@ public sealed record ThemeVariant
         {
             PlatformThemeVariant.Light => Light,
             PlatformThemeVariant.Dark => Dark,
-            _ => throw new ArgumentOutOfRangeException(nameof(themeVariant), themeVariant, null)
+            _ => throw new ArgumentOutOfRangeException(nameof(themeVariant), themeVariant, null),
         };
     }
 
-    public static explicit operator PlatformThemeVariant?(ThemeVariant themeVariant)
+    public static explicit operator PlatformThemeVariant?(ThemeVariant? themeVariant)
     {
         if (themeVariant == Light)
         {
@@ -114,7 +114,7 @@ public sealed record ThemeVariant
         {
             return PlatformThemeVariant.Dark;
         }
-        else if (themeVariant.InheritVariant is { } inheritVariant)
+        else if (themeVariant?.InheritVariant is { } inheritVariant)
         {
             return (PlatformThemeVariant?)inheritVariant;
         }

src/Avalonia.Controls/Application.cs

@@ -53,7 +53,7 @@ namespace Avalonia
         /// <inheritdoc cref="ThemeVariantScope.ActualThemeVariantProperty" />
         public static readonly StyledProperty<ThemeVariant> ActualThemeVariantProperty =
             ThemeVariantScope.ActualThemeVariantProperty.AddOwner<Application>();
-        
+
         /// <inheritdoc cref="ThemeVariantScope.RequestedThemeVariantProperty" />
         public static readonly StyledProperty<ThemeVariant?> RequestedThemeVariantProperty =
             ThemeVariantScope.RequestedThemeVariantProperty.AddOwner<Application>();
@@ -91,7 +91,7 @@ namespace Avalonia
             get => GetValue(RequestedThemeVariantProperty);
             set => SetValue(RequestedThemeVariantProperty, value);
         }
-        
+
         /// <inheritdoc />
         [System.Diagnostics.CodeAnalysis.SuppressMessage("AvaloniaProperty", "AVP1031", Justification = "This property is supposed to be a styled readonly property.")]
         [System.Diagnostics.CodeAnalysis.SuppressMessage("AvaloniaProperty", "AVP1030", Justification = "False positive.")]
@@ -201,7 +201,7 @@ namespace Avalonia
         /// as specific top levels might have different settings set-up. 
         /// </remarks>
         public IPlatformSettings? PlatformSettings => this.TryGetFeature<IPlatformSettings>();
-        
+
         event Action<IReadOnlyList<IStyle>>? IGlobalStyles.GlobalStylesAdded
         {
             add => _stylesAdded += value;
@@ -218,7 +218,7 @@ namespace Avalonia
         /// Initializes the application by loading XAML etc.
         /// </summary>
         public virtual void Initialize() { }
-        
+
         /// <inheritdoc/>
         public bool TryGetResource(object key, ThemeVariant? theme, out object? value)
         {
@@ -262,7 +262,7 @@ namespace Avalonia
                 .Bind<IGlobalStyles>().ToConstant(this)
                 .Bind<IThemeVariantHost>().ToConstant(this)
                 .Bind<IInputManager>().ToConstant(InputManager)
-                .Bind< IToolTipService>().ToConstant(new ToolTipService(InputManager))
+                .Bind<IToolTipService>().ToConstant(new ToolTipService(InputManager))
                 .Bind<IKeyboardNavigationHandler>().ToTransient<KeyboardNavigationHandler>()
                 .Bind<IDragDropDevice>().ToConstant(DragDropDevice.Instance);
 
@@ -330,20 +330,28 @@ namespace Avalonia
 
             if (change.Property == RequestedThemeVariantProperty)
             {
-                if (change.GetNewValue<ThemeVariant>() is {} themeVariant && themeVariant != ThemeVariant.Default)
-                    SetValue(ActualThemeVariantProperty, themeVariant);
-                else
-                    ClearValue(ActualThemeVariantProperty);
+                if (change.GetNewValue<ThemeVariant>() is { } themeVariant)
+                {
+                    if (themeVariant == ThemeVariant.Default)
+                    {
+                        ClearValue(ActualThemeVariantProperty);
+                    }
+                    else
+                    {
+                        SetValue(ActualThemeVariantProperty, themeVariant);
+                    }
+                }
             }
             else if (change.Property == ActualThemeVariantProperty)
             {
                 ActualThemeVariantChanged?.Invoke(this, EventArgs.Empty);
             }
         }
-        
+
         private void OnColorValuesChanged(object? sender, PlatformColorValues e)
         {
-            SetValue(ActualThemeVariantProperty, (ThemeVariant)e.ThemeVariant, BindingPriority.Template);
+            if ((RequestedThemeVariant ?? ThemeVariant.Default) == ThemeVariant.Default)
+                SetValue(ActualThemeVariantProperty, (ThemeVariant)e.ThemeVariant);
         }
     }
 }

src/Avalonia.Controls/Embedding/Offscreen/OffscreenTopLevelImpl.cs

@@ -63,7 +63,7 @@ namespace Avalonia.Controls.Embedding.Offscreen
 
         public Action<WindowTransparencyLevel>? TransparencyLevelChanged { get; set; }
 
-        public void SetFrameThemeVariant(PlatformThemeVariant themeVariant) { }
+        public void SetFrameThemeVariant(PlatformThemeVariant? themeVariant) { }
 
         public AcrylicPlatformCompensationLevels AcrylicCompensationLevels { get; } = new AcrylicPlatformCompensationLevels(1, 1, 1);
 

src/Avalonia.Controls/Platform/ITopLevelImpl.cs

@@ -137,6 +137,6 @@ namespace Avalonia.Platform
         /// Sets the <see cref="PlatformThemeVariant"/> on the frame if it should be dark or light.
         /// Also applies for the mobile status bar.
         /// </summary>
-        void SetFrameThemeVariant(PlatformThemeVariant themeVariant);
+        void SetFrameThemeVariant(PlatformThemeVariant? themeVariant);
     }
 }

src/Avalonia.Controls/TopLevel.cs

@@ -239,11 +239,6 @@ namespace Avalonia.Controls
             impl.TransparencyLevelChanged = HandleTransparencyLevelChanged;
 
             CreatePlatformImplBinding(TransparencyLevelHintProperty, hint => PlatformImpl.SetTransparencyLevelHint(hint ?? Array.Empty<WindowTransparencyLevel>()));
-            CreatePlatformImplBinding(ActualThemeVariantProperty, variant =>
-            {
-                variant ??= ThemeVariant.Default;
-                PlatformImpl?.SetFrameThemeVariant((PlatformThemeVariant?)variant ?? PlatformThemeVariant.Light);
-            });
 
             _keyboardNavigationHandler?.SetOwner(this);
             _accessKeyHandler?.SetOwner(this);
@@ -258,6 +253,16 @@ namespace Avalonia.Controls
                 SetValue(ActualThemeVariantProperty, _applicationThemeHost.ActualThemeVariant, BindingPriority.Template);
                 _applicationThemeHost.ActualThemeVariantChanged += GlobalActualThemeVariantChanged;
             }
+            CreatePlatformImplBinding(ActualThemeVariantProperty, variant =>
+            {
+                if(_applicationThemeHost is AvaloniaObject element)
+                {
+                    if (element.GetValue(ThemeVariantScope.RequestedThemeVariantProperty) is { } requestedThemeVariant)
+                        variant = requestedThemeVariant == ThemeVariant.Default ? ThemeVariant.Default : variant;
+                }
+                variant ??= ThemeVariant.Default;
+                PlatformImpl?.SetFrameThemeVariant((PlatformThemeVariant?)variant);
+            });
 
             ClientSize = impl.ClientSize;
 

src/Avalonia.DesignerSupport/Remote/Stubs.cs

@@ -196,7 +196,7 @@ namespace Avalonia.DesignerSupport.Remote
 
         public bool NeedsManagedDecorations => false;
 
-        public void SetFrameThemeVariant(PlatformThemeVariant themeVariant) { }
+        public void SetFrameThemeVariant(PlatformThemeVariant? themeVariant) { }
 
         public AcrylicPlatformCompensationLevels AcrylicCompensationLevels { get; } = new AcrylicPlatformCompensationLevels(1, 1, 1);
 

src/Avalonia.FreeDesktop/DBusPlatformSettings.cs

@@ -37,6 +37,11 @@ namespace Avalonia.FreeDesktop
                 Dispatcher.UIThread.Post(() => OnColorValuesChanged(_lastColorValues));
         }
 
+        internal void OnRequestDefaultThemeVariant()
+        {
+            _ = TryGetInitialValuesAsync();
+        }
+
         private async Task<PlatformThemeVariant?> TryGetThemeVariantAsync()
         {
             try

src/Avalonia.Native/NativePlatformSettings.cs

@@ -8,7 +8,6 @@ namespace Avalonia.Native;
 internal class NativePlatformSettings : DefaultPlatformSettings
 {
     private readonly IAvnPlatformSettings _platformSettings;
-    private PlatformColorValues? _lastColorValues;
 
     public NativePlatformSettings(IAvnPlatformSettings platformSettings)
     {
@@ -30,7 +29,7 @@ internal class NativePlatformSettings : DefaultPlatformSettings
 
         if (color > 0)
         {
-            _lastColorValues = new PlatformColorValues
+            return new PlatformColorValues
             {
                 ThemeVariant = theme,
                 ContrastPreference = contrast,
@@ -39,25 +38,17 @@ internal class NativePlatformSettings : DefaultPlatformSettings
         }
         else
         {
-            _lastColorValues = new PlatformColorValues
+            return new PlatformColorValues
             {
                 ThemeVariant = theme,
                 ContrastPreference = contrast
             };
         }
-
-        return _lastColorValues;
     }
 
     public void OnColorValuesChanged()
     {
-        var oldColorValues = _lastColorValues;
-        var colorValues = GetColorValues();
-
-        if (oldColorValues != colorValues)
-        {
-            OnColorValuesChanged(colorValues);
-        }
+        OnColorValuesChanged(GetColorValues());
     }
 
     private class ColorsChangeCallback : NativeCallbackBase, IAvnActionCallback

src/Avalonia.Native/TopLevelImpl.cs

@@ -158,7 +158,7 @@ internal class TopLevelImpl : ITopLevelImpl, IFramebufferPlatformSurface
     }
 
     public AcrylicPlatformCompensationLevels AcrylicCompensationLevels { get; } = new AcrylicPlatformCompensationLevels(1, 0, 0);
-    public virtual void SetFrameThemeVariant(PlatformThemeVariant themeVariant)
+    public virtual void SetFrameThemeVariant(PlatformThemeVariant? themeVariant)
     {
         //noop
     }

src/Avalonia.Native/WindowImplBase.cs

@@ -68,8 +68,16 @@ namespace Avalonia.Native
             Native?.Resize(clientSize.Width, clientSize.Height, (AvnPlatformResizeReason)reason);
         }
         
-        public override void SetFrameThemeVariant(PlatformThemeVariant themeVariant)
+        public override void SetFrameThemeVariant(PlatformThemeVariant? themeVariant)
         {
+            var settings = AvaloniaLocator.Current.GetService<IPlatformSettings>();
+
+            if (themeVariant is null && settings is NativePlatformSettings typedSettings)
+            {
+                typedSettings.OnColorValuesChanged();
+            }
+
+            themeVariant ??= settings?.GetColorValues().ThemeVariant ?? PlatformThemeVariant.Light;
             Native?.SetFrameThemeVariant((AvnPlatformThemeVariant)themeVariant);
         }
 

src/Avalonia.Wayland/WindowImplBase.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.Threading.Tasks;
 using Avalonia.Controls;
 using Avalonia.Controls.Platform;
+using Avalonia.FreeDesktop;
 using Avalonia.Input;
 using Avalonia.Input.Platform;
 using Avalonia.Input.Raw;
@@ -76,7 +77,14 @@ internal abstract partial class WindowBaseImpl : IWindowBaseImpl
     public WindowTransparencyLevel TransparencyLevel { get; } = WindowTransparencyLevel.Transparent;
     public AcrylicPlatformCompensationLevels AcrylicCompensationLevels { get; } = default;
     public void SetTransparencyLevelHint(IReadOnlyList<WindowTransparencyLevel> transparencyLevels) { }
-    public void SetFrameThemeVariant(PlatformThemeVariant themeVariant) { }
+
+    public async void SetFrameThemeVariant(PlatformThemeVariant? themeVariant)
+    {
+        if (themeVariant == null && AvaloniaLocator.Current.GetService<IPlatformSettings>() is DBusPlatformSettings platformSettings)
+        {
+            platformSettings.OnRequestDefaultThemeVariant();
+        }
+    }
 
     public Action? Closed { get; set; }
     public Action? LostFocus { get; set; }

src/Avalonia.X11/X11Window.cs

@@ -1662,7 +1662,13 @@ namespace Avalonia.X11
         public WindowTransparencyLevel TransparencyLevel =>
             _transparencyHelper?.CurrentLevel ?? WindowTransparencyLevel.None;
 
-        public void SetFrameThemeVariant(PlatformThemeVariant themeVariant) { }
+        public async void SetFrameThemeVariant(PlatformThemeVariant? themeVariant)
+        {
+            if (themeVariant == null && AvaloniaLocator.Current.GetService<IPlatformSettings>() is DBusPlatformSettings platformSettings)
+            {
+                platformSettings.OnRequestDefaultThemeVariant();
+            }
+        }
 
         public AcrylicPlatformCompensationLevels AcrylicCompensationLevels { get; } = new AcrylicPlatformCompensationLevels(1, 0.8, 0.8);
 

src/Browser/Avalonia.Browser/BrowserPlatformSettings.cs

@@ -37,6 +37,11 @@ internal class BrowserPlatformSettings : DefaultPlatformSettings
         _isHighContrast = isHighContrast;
         OnColorValuesChanged(GetColorValues());
     }
+
+    public void OnValuesChanged()
+    {
+        OnColorValuesChanged(GetColorValues());
+    }
     
     private void EnsureBackend()
     {

src/Browser/Avalonia.Browser/BrowserTopLevelImpl.cs

@@ -144,9 +144,13 @@ namespace Avalonia.Browser
         public Action? LostFocus { get; set; }
         public WindowTransparencyLevel TransparencyLevel => WindowTransparencyLevel.None;
 
-        public void SetFrameThemeVariant(PlatformThemeVariant themeVariant)
+        public void SetFrameThemeVariant(PlatformThemeVariant? themeVariant)
         {
             // not in the standard, but we potentially can use "apple-mobile-web-app-status-bar-style" for iOS and "theme-color" for android.
+            if (themeVariant == null && AvaloniaLocator.Current.GetService<IPlatformSettings>() is BrowserPlatformSettings platformSettings)
+            {
+                platformSettings.OnValuesChanged();
+            }
         }
 
         public AcrylicPlatformCompensationLevels AcrylicCompensationLevels { get; }

src/Headless/Avalonia.Headless/HeadlessWindowImpl.cs

@@ -438,7 +438,7 @@ namespace Avalonia.Headless
             
         }
         
-        public void SetFrameThemeVariant(PlatformThemeVariant themeVariant)
+        public void SetFrameThemeVariant(PlatformThemeVariant? themeVariant)
         {
             
         }

src/Linux/Avalonia.LinuxFramebuffer/FramebufferToplevelImpl.cs

@@ -78,7 +78,7 @@ using Avalonia.Rendering.Composition;
 
         public WindowTransparencyLevel TransparencyLevel => WindowTransparencyLevel.None;
 
-        public void SetFrameThemeVariant(PlatformThemeVariant themeVariant) { }
+        public void SetFrameThemeVariant(PlatformThemeVariant? themeVariant) { }
 
         public AcrylicPlatformCompensationLevels AcrylicCompensationLevels { get; } = new AcrylicPlatformCompensationLevels(1, 1, 1);
         public object? TryGetFeature(Type featureType) => null;

src/Windows/Avalonia.Win32/SwapChainTopLevelImpl.cs

@@ -99,7 +99,7 @@ internal class SwapChainTopLevelImpl : ITopLevelImpl
 
     public void SetTransparencyLevelHint(IReadOnlyList<WindowTransparencyLevel> transparencyLevels) { }
 
-    public void SetFrameThemeVariant(PlatformThemeVariant themeVariant) { }
+    public void SetFrameThemeVariant(PlatformThemeVariant? themeVariant) { }
 
     /// <summary>
     /// Optional IME implementation provided by the host.

src/Windows/Avalonia.Win32/Win32PlatformSettings.cs

@@ -10,9 +10,7 @@ internal class Win32PlatformSettings : DefaultPlatformSettings
 {
     private static readonly Lazy<bool> s_uiSettingsSupported = new(() =>
         WinRTApiInformation.IsTypePresent("Windows.UI.ViewManagement.UISettings")
-        && WinRTApiInformation.IsTypePresent("Windows.UI.ViewManagement.AccessibilitySettings")); 
-
-    private PlatformColorValues? _lastColorValues;
+        && WinRTApiInformation.IsTypePresent("Windows.UI.ViewManagement.AccessibilitySettings"));
 
     public override Size GetTapSize(PointerType type)
     {
@@ -54,7 +52,7 @@ internal class Win32PlatformSettings : DefaultPlatformSettings
             // - Night sky - High Contrast #2
             // Only "Desert" one can be considered a "light" preference. 
             using var highContrastScheme = new HStringInterop(accessibilitySettings.HighContrastScheme);
-            return _lastColorValues = new PlatformColorValues
+            return new PlatformColorValues
             {
                 ThemeVariant = highContrastScheme.Value?.Contains("White") == true ?
                     PlatformThemeVariant.Light :
@@ -67,7 +65,7 @@ internal class Win32PlatformSettings : DefaultPlatformSettings
         else
         {
             var background = uiSettings.GetColorValue(UIColorType.Background).ToAvalonia();
-            return _lastColorValues = new PlatformColorValues
+            return new PlatformColorValues
             {
                 ThemeVariant = background.R + background.G + background.B < (255 * 3 - background.R - background.G - background.B) ?
                     PlatformThemeVariant.Dark :
@@ -80,12 +78,6 @@ internal class Win32PlatformSettings : DefaultPlatformSettings
     
     internal void OnColorValuesChanged()
     {
-        var oldColorValues = _lastColorValues;
-        var colorValues = GetColorValues();
-
-        if (oldColorValues != colorValues)
-        {
-            OnColorValuesChanged(colorValues);
-        }
+        OnColorValuesChanged(GetColorValues());
     }
 }

src/Windows/Avalonia.Win32/WindowImpl.cs

@@ -948,12 +948,12 @@ namespace Avalonia.Win32
             }
         }
 
-        public unsafe void SetFrameThemeVariant(PlatformThemeVariant themeVariant)
+        public unsafe void SetFrameThemeVariant(PlatformThemeVariant? themeVariant)
         {
-            _currentThemeVariant = themeVariant;
+            _currentThemeVariant = themeVariant ?? Win32Platform.Instance.PlatformSettings.GetColorValues().ThemeVariant;
             if (Win32Platform.WindowsVersion.Build >= 22000)
             {
-                var pvUseBackdropBrush = themeVariant == PlatformThemeVariant.Dark ? 1 : 0;
+                var pvUseBackdropBrush = _currentThemeVariant == PlatformThemeVariant.Dark ? 1 : 0;
                 DwmSetWindowAttribute(
                     _hwnd,
                     (int)DwmWindowAttribute.DWMWA_USE_IMMERSIVE_DARK_MODE,
@@ -964,6 +964,8 @@ namespace Avalonia.Win32
                     SetTransparencyMica();
                 }
             }
+
+            (Win32Platform.Instance.PlatformSettings as Win32PlatformSettings)?.OnColorValuesChanged();
         }
 
         protected virtual IntPtr CreateWindowOverride(ushort atom)

src/iOS/Avalonia.iOS/AvaloniaView.cs

@@ -254,8 +254,13 @@ namespace Avalonia.iOS
 
             public WindowTransparencyLevel TransparencyLevel => WindowTransparencyLevel.None;
 
-            public void SetFrameThemeVariant(PlatformThemeVariant themeVariant)
+            public void SetFrameThemeVariant(PlatformThemeVariant? themeVariant)
             {
+                if (themeVariant is null && AvaloniaLocator.Current.GetService<IPlatformSettings>() is PlatformSettings settings)
+                {
+                    settings.OnColorValuesChanged();
+                }
+
 #if !TVOS
                 // TODO adjust status bar depending on full screen mode.
                 if ((OperatingSystem.IsIOSVersionAtLeast(13)

src/iOS/Avalonia.iOS/PlatformSettings.cs

@@ -61,4 +61,9 @@ internal class PlatformSettings : DefaultPlatformSettings
             OnColorValuesChanged(colorValues);
         }
     }
+
+    internal void OnColorValuesChanged()
+    {
+        OnColorValuesChanged(GetColorValues());
+    }
 }

tests/Avalonia.UnitTests/CompositorTestServices.cs

@@ -205,7 +205,7 @@ public class CompositorTestServices : IDisposable
 
         public WindowTransparencyLevel TransparencyLevel => WindowTransparencyLevel.None;
 
-        public void SetFrameThemeVariant(PlatformThemeVariant themeVariant)
+        public void SetFrameThemeVariant(PlatformThemeVariant? themeVariant)
         {
         }