Allow only Light and Dark in the ColorPaletteResourcesCollection

samples/ControlCatalog/App.xaml

@@ -28,6 +28,9 @@
       </ResourceDictionary.ThemeDictionaries>
 
       <!-- Styles attached dynamically depending on current theme (simple or fluent) -->
+      <FluentTheme x:Key="FluentTheme">
+      </FluentTheme>
+      <SimpleTheme x:Key="SimpleTheme" />
       <StyleInclude x:Key="DataGridFluent" Source="avares://Avalonia.Controls.DataGrid/Themes/Fluent.xaml" />
       <StyleInclude x:Key="DataGridSimple" Source="avares://Avalonia.Controls.DataGrid/Themes/Simple.xaml" />
       <StyleInclude x:Key="ColorPickerFluent" Source="avares://Avalonia.Controls.ColorPicker/Themes/Fluent/Fluent.xaml" />

samples/ControlCatalog/App.xaml.cs

@@ -30,8 +30,8 @@ namespace ControlCatalog
 
             AvaloniaXamlLoader.Load(this);
 
-            _fluentTheme = new FluentTheme();
-            _simpleTheme = new SimpleTheme();
+            _fluentTheme = (FluentTheme)Resources["FluentTheme"]!;
+            _simpleTheme = (SimpleTheme)Resources["SimpleTheme"]!;
             _colorPickerFluent = (IStyle)Resources["ColorPickerFluent"]!;
             _colorPickerSimple = (IStyle)Resources["ColorPickerSimple"]!;
             _dataGridFluent = (IStyle)Resources["DataGridFluent"]!;

src/Avalonia.Themes.Fluent/ColorPaletteResourcesCollection.cs

@@ -10,12 +10,18 @@ internal class ColorPaletteResourcesCollection : AvaloniaDictionary<ThemeVariant
     public ColorPaletteResourcesCollection() : base(2)
     {
         this.ForEachItem(
-            (_, x) =>
+            (key, x) =>
             {
                 if (Owner is not null)
                 {
                     x.PropertyChanged += Palette_PropertyChanged;
                 }
+
+                if (key != ThemeVariant.Dark && key != ThemeVariant.Light)
+                {
+                    throw new InvalidOperationException(
+                        $"{nameof(FluentTheme)}.{nameof(FluentTheme.Palettes)} only supports Light and Dark variants.");
+                }
             },
             (_, x) =>
             {
@@ -30,22 +36,15 @@ internal class ColorPaletteResourcesCollection : AvaloniaDictionary<ThemeVariant
     public bool HasResources => Count > 0;
     public bool TryGetResource(object key, ThemeVariant? theme, out object? value)
     {
-        if (theme is not null)
+        if (theme == null || theme == ThemeVariant.Default)
         {
-            if (base.TryGetValue(theme, out var themePaletteResources)
-                && themePaletteResources.TryGetResource(key, theme, out value))
-            {
-                return true;
-            }
+            theme = ThemeVariant.Light;
         }
 
-        if (theme != ThemeVariant.Default)
+        if (base.TryGetValue(theme, out var themePaletteResources)
+            && themePaletteResources.TryGetResource(key, theme, out value))
         {
-            if (base.TryGetValue(ThemeVariant.Default, out var defaultPaletteResources)
-                && defaultPaletteResources.TryGetResource(key, ThemeVariant.Default, out value))
-            {
-                return true;
-            }
+            return true;
         }
 
         value = null;