Update API layer

samples/ControlCatalog/Pages/ThemePage.axaml

@@ -54,7 +54,7 @@
     </ResourceDictionary>
   </UserControl.Resources>
 
-  <ThemeControl x:Name="ThemeControl">
+  <ThemeVariantScope x:Name="ThemeVariantScope">
     <Border Background="{DynamicResource DemoBackground}"
             VerticalAlignment="Top"
             HorizontalAlignment="Left"
@@ -75,5 +75,5 @@
         <Button Grid.Column="1" Grid.Row="6" Content="Login" HorizontalAlignment="Stretch" />
       </Grid>
     </Border>
-  </ThemeControl>
+  </ThemeVariantScope>
 </UserControl>

samples/ControlCatalog/Pages/ThemePage.axaml.cs

@@ -1,6 +1,7 @@
 using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Markup.Xaml;
+using Avalonia.Styling;
 
 namespace ControlCatalog.Pages
 {
@@ -13,7 +14,7 @@ public ThemePage()
             AvaloniaXamlLoader.Load(this);
 
             var selector = this.FindControl<ComboBox>("Selector")!;
-            var themeControl = this.FindControl<ThemeControl>("ThemeControl")!;
+            var themeVariantScope = this.FindControl<ThemeVariantScope>("ThemeVariantScope")!;
 
             selector.Items = new[]
             {
@@ -29,11 +30,11 @@ public ThemePage()
                 var theme = (ThemeVariant)selector.SelectedItem!;
                 if ((string)theme.Key == "Default")
                 {
-                    themeControl.ClearValue(ThemeControl.ThemeVariantProperty);
+                    themeVariantScope.ClearValue(ThemeVariantProperty);
                 }
                 else
                 {
-                    themeControl.ThemeVariant = theme;
+                    themeVariantScope.ThemeVariant = theme;
                 }
             };
         }

src/Avalonia.Base/Controls/IResourceDictionary.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using Avalonia.Styling;
 
 #nullable enable
 

src/Avalonia.Base/Controls/IResourceNode.cs

@@ -1,4 +1,5 @@
 using Avalonia.Metadata;
+using Avalonia.Styling;
 
 namespace Avalonia.Controls
 {

src/Avalonia.Base/Controls/ResourceDictionary.cs

@@ -5,6 +5,7 @@
 using System.Linq;
 using Avalonia.Collections;
 using Avalonia.Controls.Templates;
+using Avalonia.Styling;
 
 namespace Avalonia.Controls
 {

src/Avalonia.Base/Controls/ResourceNodeExtensions.cs

@@ -1,5 +1,6 @@
 using System;
 using Avalonia.Reactive;
+using Avalonia.Styling;
 
 #nullable enable
 
@@ -38,9 +39,7 @@ public static bool TryFindResource(this IResourceHost control, object key, out o
             control = control ?? throw new ArgumentNullException(nameof(control));
             key = key ?? throw new ArgumentNullException(nameof(key));
 
-            var theme = AvaloniaLocator.Current.GetService<IApplicationThemeHost>()?.ThemeVariant;
-
-            return control.TryFindResource(key, theme, out value);
+            return control.TryFindResource(key, null, out value);
         }
 
         /// <summary>
@@ -98,9 +97,7 @@ public static bool TryGetResource(this IResourceHost control, object key, out ob
             control = control ?? throw new ArgumentNullException(nameof(control));
             key = key ?? throw new ArgumentNullException(nameof(key));
 
-            var theme = AvaloniaLocator.Current.GetService<IApplicationThemeHost>()?.ThemeVariant;
-
-            return control.TryGetResource(key, theme, out value);
+            return control.TryGetResource(key, null, out value);
         }
 
         public static IObservable<object?> GetResourceObservable(
@@ -141,7 +138,7 @@ public ResourceObservable(IResourceHost target, object key, Func<object?, object
             protected override void Initialize()
             {
                 _target.ResourcesChanged += ResourcesChanged;
-                if (_target is IThemeStyleable themeStyleable)
+                if (_target is IStyleable themeStyleable)
                 {
                     themeStyleable.ThemeVariantChanged += ThemeVariantChanged;
                 }
@@ -150,7 +147,7 @@ protected override void Initialize()
             protected override void Deinitialize()
             {
                 _target.ResourcesChanged -= ResourcesChanged;
-                if (_target is IThemeStyleable themeStyleable)
+                if (_target is IStyleable themeStyleable)
                 {
                     themeStyleable.ThemeVariantChanged -= ThemeVariantChanged;
                 }
@@ -173,8 +170,8 @@ private void ThemeVariantChanged(object? sender, EventArgs e)
 
             private object? GetValue()
             {
-                if (!(_target is IThemeStyleable themeStyleable)
-                    || !themeStyleable.TryFindResource(_key, themeStyleable.ThemeVariant, out var value))
+                if (_target is not IStyleable themeStyleable
+                    || !_target.TryFindResource(_key, themeStyleable.ThemeVariant, out var value))
                 {
                     value = _target.FindResource(_key) ?? AvaloniaProperty.UnsetValue;
                 }
@@ -202,7 +199,7 @@ protected override void Initialize()
                 _target.OwnerChanged += OwnerChanged;
                 _owner = _target.Owner;
 
-                if (_owner is object)
+                if (_owner is not null)
                 {
                     _owner.ResourcesChanged += ResourcesChanged;
                 }
@@ -216,40 +213,40 @@ protected override void Deinitialize()
 
             protected override void Subscribed(IObserver<object?> observer, bool first)
             {
-                if (_target.Owner is object)
+                if (_target.Owner is not null)
                 {
                     observer.OnNext(GetValue());
                 }
             }
 
             private void PublishNext()
             {
-                if (_target.Owner is object)
+                if (_target.Owner is not null)
                 {
                     PublishNext(GetValue());
                 }
             }
 
             private void OwnerChanged(object? sender, EventArgs e)
             {
-                if (_owner is object)
+                if (_owner is not null)
                 {
                     _owner.ResourcesChanged -= ResourcesChanged;
                 }
-                if (_owner is IThemeStyleable themeStyleable)
+                if (_owner is IStyleable styleable)
                 {
-                    themeStyleable.ThemeVariantChanged -= ThemeVariantChanged;
+                    styleable.ThemeVariantChanged -= ThemeVariantChanged;
                 }
 
                 _owner = _target.Owner;
 
-                if (_owner is object)
+                if (_owner is not null)
                 {
                     _owner.ResourcesChanged += ResourcesChanged;
                 }
-                if (_owner is IThemeStyleable themeStyleable2)
+                if (_owner is IStyleable styleable2)
                 {
-                    themeStyleable2.ThemeVariantChanged += ThemeVariantChanged;
+                    styleable2.ThemeVariantChanged += ThemeVariantChanged;
                 }
 
                 PublishNext();
@@ -267,9 +264,9 @@ private void ThemeVariantChanged(object? sender, EventArgs e)
 
             private object? GetValue()
             {
-                if (!(_target.Owner is IThemeStyleable themeStyleable)
+                if (!(_target.Owner is IStyleable themeStyleable)
                     || themeStyleable.ThemeVariant is null
-                    || !themeStyleable.TryFindResource(_key, themeStyleable.ThemeVariant, out var value))
+                    || !_target.Owner.TryFindResource(_key, themeStyleable.ThemeVariant, out var value))
                 {
                     value = _target.Owner?.FindResource(_key) ?? AvaloniaProperty.UnsetValue;
                 }

src/Avalonia.Base/StyledElement.cs

@@ -60,6 +60,15 @@ public class StyledElement : Animatable, IDataContextProvider, IStyledElement, I
         public static readonly StyledProperty<ControlTheme?> ThemeProperty =
             AvaloniaProperty.Register<StyledElement, ControlTheme?>(nameof(Theme));
 
+        /// <summary>
+        /// Defines the <see cref="ThemeVariant"/> property.
+        /// </summary>
+        public static readonly StyledProperty<ThemeVariant> ThemeVariantProperty =
+            AvaloniaProperty.Register<StyledElement, ThemeVariant>(
+                nameof(ThemeVariant),
+                inherits: true,
+                defaultValue: ThemeVariant.Light);
+
         private static readonly ControlTheme s_invalidTheme = new ControlTheme();
         private int _initCount;
         private string? _name;
@@ -246,6 +255,10 @@ public ControlTheme? Theme
             set => SetValue(ThemeProperty, value);
         }
 
+        ThemeVariant IStyleable.ThemeVariant => GetValue(ThemeVariantProperty);
+
+        public event EventHandler? ThemeVariantChanged;
+
         /// <summary>
         /// Gets the styled element's logical children.
         /// </summary>
@@ -659,6 +672,10 @@ protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs chang
 
                 InvalidateStyles();
             }
+            else if (change.Property == ThemeVariantProperty)
+            {
+                ThemeVariantChanged?.Invoke(this, EventArgs.Empty);
+            }
         }
 
         private static void DataContextNotifying(IAvaloniaObject o, bool updateStarted)

src/Avalonia.Base/Themes/IThemeStyleable.cs → src/Avalonia.Base/Styling/IApplicationThemeVariantHost.cs

@@ -1,13 +1,12 @@
 using System;
-
 using Avalonia.Controls;
 
-namespace Avalonia;
+namespace Avalonia.Styling;
 
 /// <summary>
-/// Interface for elements that supports dynamic theme.
+/// Interface for a host element with a root theme.
 /// </summary>
-public interface IThemeStyleable : IResourceHost
+public interface IApplicationThemeVariantHost : IResourceHost
 {
     /// <summary>
     /// Gets the UI theme that is used by the control (and its child elements) for resource determination.

src/Avalonia.Base/Styling/IStyleable.cs

@@ -31,6 +31,16 @@ public interface IStyleable : IAvaloniaObject, INamed
         /// </summary>
         ControlTheme? GetEffectiveTheme();
 
+        /// <summary>
+        /// Gets the UI theme that is used by the control (and its child elements) for resource determination.
+        /// </summary>
+        ThemeVariant ThemeVariant { get; }
+
+        /// <summary>
+        /// Raised when the theme is changed on the element or an ancestor of the element.
+        /// </summary>
+        event EventHandler? ThemeVariantChanged;
+
         /// <summary>
         /// Notifies the element that a style has been applied.
         /// </summary>

src/Avalonia.Base/Themes/ThemeVariant.cs → src/Avalonia.Base/Styling/ThemeVariant.cs

@@ -1,10 +1,10 @@
 using System;
 using System.ComponentModel;
 
-namespace Avalonia;
+namespace Avalonia.Styling;
 
 [TypeConverter(typeof(ThemeVariantTypeConverter))]
-public class ThemeVariant
+public class ThemeVariant : IEquatable<ThemeVariant>
 {
     public ThemeVariant(object key)
     {
@@ -31,8 +31,17 @@ public override int GetHashCode()
 
     public override bool Equals(object? obj)
     {
+        if (ReferenceEquals(null, obj)) return false;
+        if (ReferenceEquals(this, obj)) return true;
         return obj is ThemeVariant theme && Key.Equals(theme.Key);
     }
+
+    public bool Equals(ThemeVariant? obj)
+    {
+        if (ReferenceEquals(null, obj)) return false;
+        if (ReferenceEquals(this, obj)) return true;
+        return Key.Equals(obj.Key);
+    }
 
     public override string ToString()
     {

src/Avalonia.Base/Themes/ThemeVariantTypeConverter.cs → src/Avalonia.Base/Styling/ThemeVariantTypeConverter.cs

@@ -2,7 +2,7 @@
 using System.ComponentModel;
 using System.Globalization;
 
-namespace Avalonia;
+namespace Avalonia.Styling;
 
 public class ThemeVariantTypeConverter : TypeConverter
 {

src/Avalonia.Controls/Application.cs

@@ -31,7 +31,7 @@ namespace Avalonia
     /// method.
     /// - Tracks the lifetime of the application.
     /// </remarks>
-    public class Application : AvaloniaObject, IDataContextProvider, IGlobalDataTemplates, IGlobalStyles, IApplicationThemeHost, IApplicationPlatformEvents
+    public class Application : AvaloniaObject, IDataContextProvider, IGlobalDataTemplates, IGlobalStyles, IApplicationThemeVariantHost, IApplicationPlatformEvents
     {
         /// <summary>
         /// The application-global data templates.
@@ -53,9 +53,9 @@ public class Application : AvaloniaObject, IDataContextProvider, IGlobalDataTemp
         public static readonly StyledProperty<object?> DataContextProperty =
             StyledElement.DataContextProperty.AddOwner<Application>();
 
-        /// <inheritdoc cref="ThemeControl.ThemeVariantProperty" />
+        /// <inheritdoc cref="StyledElement.ThemeVariantProperty" />
         public static readonly StyledProperty<ThemeVariant> ThemeVariantProperty =
-            ThemeControl.ThemeVariantProperty.AddOwner<Application>();
+            StyledElement.ThemeVariantProperty.AddOwner<Application>();
 
         /// <inheritdoc/>
         public event EventHandler<ResourcesChangedEventArgs>? ResourcesChanged;
@@ -87,7 +87,7 @@ public object? DataContext
             set { SetValue(DataContextProperty, value); }
         }
 
-        /// <inheritdoc cref="ThemeControl.ThemeVariant" />
+        /// <inheritdoc cref="IStyleable.ThemeVariant" />
         public ThemeVariant ThemeVariant
         {
             get => GetValue(ThemeVariantProperty);
@@ -245,7 +245,7 @@ public virtual void RegisterServices()
                 .Bind<IAccessKeyHandler>().ToTransient<AccessKeyHandler>()
                 .Bind<IGlobalDataTemplates>().ToConstant(this)
                 .Bind<IGlobalStyles>().ToConstant(this)
-                .Bind<IApplicationThemeHost>().ToConstant(this)
+                .Bind<IApplicationThemeVariantHost>().ToConstant(this)
                 .Bind<IFocusManager>().ToConstant(FocusManager)
                 .Bind<IInputManager>().ToConstant(InputManager)
                 .Bind<IKeyboardNavigationHandler>().ToTransient<KeyboardNavigationHandler>()

src/Avalonia.Controls/Control.cs

@@ -172,10 +172,7 @@ public FlowDirection FlowDirection
             get => GetValue(FlowDirectionProperty);
             set => SetValue(FlowDirectionProperty, value);
         }
-
-        ThemeVariant IThemeStyleable.ThemeVariant => GetValue(ThemeControl.ThemeVariantProperty);
-        public event EventHandler? ThemeVariantChanged;
-
+
         /// <summary>
         /// Occurs when the user has completed a context input gesture, such as a right-click.
         /// </summary>
@@ -551,10 +548,6 @@ protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs chang
                     }
                 }
             }
-            else if (change.Property == ThemeControl.ThemeVariantProperty)
-            {
-                ThemeVariantChanged?.Invoke(this, EventArgs.Empty);
-            }
         }
 
         /// <summary>

src/Avalonia.Controls/IControl.cs

@@ -15,8 +15,7 @@ public interface IControl : IVisual,
         ILayoutable,
         IInputElement,
         INamed,
-        IStyledElement,
-        IThemeStyleable
+        IStyledElement
     {
         new IControl? Parent { get; }
     }