feat: Theme toggler

src/Ursa/Controls/ThemeSelector/ThemeSelectorBase.cs

@@ -0,0 +1,65 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Controls.Primitives;
+using Avalonia.LogicalTree;
+using Avalonia.Styling;
+
+namespace Ursa.Controls;
+
+public abstract class ThemeSelectorBase: TemplatedControl
+{
+    private Application? _application;
+    private ThemeVariantScope? _scope;
+    
+    public static readonly StyledProperty<ThemeVariant?> SelectedThemeProperty = AvaloniaProperty.Register<ThemeSelectorBase, ThemeVariant?>(
+        nameof(SelectedTheme));
+
+    public ThemeVariant? SelectedTheme
+    {
+        get => GetValue(SelectedThemeProperty);
+        set => SetValue(SelectedThemeProperty, value);
+    }
+
+    public static readonly StyledProperty<ThemeVariantScope?> TargetScopeProperty =
+        AvaloniaProperty.Register<ThemeSelectorBase, ThemeVariantScope?>(
+            nameof(TargetScope));
+
+    public ThemeVariantScope? TargetScope
+    {
+        get => GetValue(TargetScopeProperty);
+        set => SetValue(TargetScopeProperty, value);
+    }
+
+    static ThemeSelectorBase()
+    {
+        SelectedThemeProperty.Changed.AddClassHandler<ThemeSelectorBase, ThemeVariant?>((s, e) => s.OnSelectedThemeChanged(e));
+    }
+
+    protected override void OnAttachedToVisualTree(VisualTreeAttachmentEventArgs e)
+    {
+        base.OnAttachedToVisualTree(e);
+        _application = Application.Current;
+        _scope = this.GetLogicalAncestors().FirstOrDefault(a => a is ThemeVariantScope) as ThemeVariantScope;
+    }
+
+    protected virtual void OnSelectedThemeChanged(AvaloniaPropertyChangedEventArgs<ThemeVariant?> args)
+    {
+        ThemeVariant? newTheme = args.NewValue.Value;
+        if (newTheme is null) return;
+        if (TargetScope is not null)
+        {
+            TargetScope.RequestedThemeVariant = newTheme;
+            return;
+        }
+        if (_scope is not null)
+        {
+            _scope.RequestedThemeVariant = newTheme;
+            return;
+        }
+        if (_application is not null)
+        {
+            _application.RequestedThemeVariant = newTheme;
+            return;
+        }
+    }
+}