fix reseting actual theme variant

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

@@ -39,6 +39,7 @@
                       HorizontalAlignment="Stretch"
                       VerticalAlignment="Stretch">
                     <StackPanel Orientation="Vertical"
+                                Spacing="5"
                                 HorizontalAlignment="Center"
                                 VerticalAlignment="Center">
                         <Label HorizontalAlignment="Left">Options:</Label>
@@ -47,6 +48,11 @@
                         <CheckBox IsChecked="{Binding AutoSafeAreaPadding}">Automatic Paddings</CheckBox>
                         <CheckBox IsChecked="{Binding HideSystemBars}">Hide System Bars</CheckBox>
                         <TextBox Width="200" Watermark="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/Platform/SkiaPlatform/TopLevelImpl.cs

@@ -9,6 +9,7 @@ using Android.Text;
 using Android.Views;
 using Android.Views.InputMethods;
 using AndroidX.AppCompat.App;
+using AndroidX.Core.View;
 using Avalonia.Android.Platform.Input;
 using Avalonia.Android.Platform.Specific;
 using Avalonia.Android.Platform.Specific.Helpers;
@@ -281,10 +282,17 @@ namespace Avalonia.Android.Platform.SkiaPlatform
                 };
             }
 
-            AppCompatDelegate.DefaultNightMode = themeVariant == null ? AppCompatDelegate.ModeNightFollowSystem :
+            // 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;
 
-            if (AppCompatDelegate.DefaultNightMode == AppCompatDelegate.ModeNightFollowSystem && _view.Context is { } context
+            AppCompatDelegate.DefaultNightMode = nightMode;
+
+            if (nightMode == AppCompatDelegate.ModeNightFollowSystem && _view.Context is { } context
                 && context.Resources?.Configuration is { } config)
             {
                 var settings =

src/Avalonia.Base/Styling/ThemeVariant.cs

@@ -100,7 +100,7 @@ public sealed record ThemeVariant
         {
             PlatformThemeVariant.Light => Light,
             PlatformThemeVariant.Dark => Dark,
-            _ => Default,
+            _ => throw new ArgumentOutOfRangeException(nameof(themeVariant), themeVariant, null),
         };
     }
 

src/Avalonia.Controls/Application.cs

@@ -54,7 +54,7 @@ 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>();
@@ -106,7 +106,7 @@ 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.")]
@@ -216,7 +216,7 @@ 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;
@@ -233,7 +233,7 @@ 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)
         {
@@ -286,7 +286,7 @@ namespace Avalonia
                 .Bind<IThemeVariantHost>().ToConstant(this)
                 .Bind<IFocusManager>().ToConstant(focusManager)
                 .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);
 
@@ -304,10 +304,10 @@ namespace Avalonia
         public virtual void OnFrameworkInitializationCompleted()
         {
         }
-        
+
         void IApplicationPlatformEvents.RaiseUrlsOpened(string[] urls)
         {
-            UrlsOpened?.Invoke(this, new UrlOpenedEventArgs (urls));
+            UrlsOpened?.Invoke(this, new UrlOpenedEventArgs(urls));
         }
 
         private string? _name;
@@ -361,13 +361,13 @@ namespace Avalonia
             {
                 if (change.GetNewValue<ThemeVariant>() is { } themeVariant)
                 {
-                    if (themeVariant == ThemeVariant.Default && PlatformSettings?.GetColorValues() is { } currentColors)
+                    if (themeVariant == ThemeVariant.Default)
                     {
-                        SetValue(ActualThemeVariantProperty, (ThemeVariant)currentColors.ThemeVariant);
+                        ClearValue(ActualThemeVariantProperty);
                     }
                     else
                     {
-                        SetValue(ActualThemeVariantProperty, themeVariant);   
+                        SetValue(ActualThemeVariantProperty, themeVariant);
                     }
                 }
             }
@@ -380,7 +380,7 @@ namespace Avalonia
         private void OnColorValuesChanged(object? sender, PlatformColorValues e)
         {
             if ((RequestedThemeVariant ?? ThemeVariant.Default) == ThemeVariant.Default)
-                SetCurrentValue(ActualThemeVariantProperty, (ThemeVariant)e.ThemeVariant);
+                SetValue(ActualThemeVariantProperty, (ThemeVariant)e.ThemeVariant);
         }
     }
 }

src/Avalonia.Controls/TopLevel.cs

@@ -929,7 +929,7 @@ namespace Avalonia.Controls
 
         private void GlobalActualThemeVariantChanged(object? sender, EventArgs e)
         {
-            SetCurrentValue(ActualThemeVariantProperty, ((IThemeVariantHost)sender!).ActualThemeVariant);
+            SetValue(ActualThemeVariantProperty, ((IThemeVariantHost)sender!).ActualThemeVariant, BindingPriority.Template);
         }
 
         private void SceneInvalidated(object? sender, SceneInvalidatedEventArgs e)