xaml-csharp-development-skill-for-avalonia

WinUI Resource Lookup Order and ThemeResource to Avalonia

Table of Contents

1. Scope and APIs
2. Concept Mapping
3. Conversion Example
4. Migration Notes

Scope and APIs

Primary WinUI APIs:

• ResourceDictionary, StaticResource, ThemeResource
• ResourceDictionary.MergedDictionaries, ThemeDictionaries

Primary Avalonia APIs:

• ResourceDictionary, StaticResource, DynamicResource
• ResourceDictionary.MergedDictionaries, ThemeDictionaries
• ResourceInclude, StyleInclude
• Application.TryGetResource(…)

Concept Mapping

WinUI idiom	Avalonia idiom
StaticResource for stable values	StaticResource
ThemeResource for theme-variant values	DynamicResource + ThemeDictionaries
merged dictionary layering	merged dictionary layering
resource probe at runtime	TryGetResource(key, theme, out value)

Conversion Example

WinUI XAML:

<Page.Resources>
  <ResourceDictionary>
    <ResourceDictionary.ThemeDictionaries>
      <ResourceDictionary x:Key="Light">
        <SolidColorBrush x:Key="AccentBrush" Color="#0063B1" />
      </ResourceDictionary>
      <ResourceDictionary x:Key="Dark">
        <SolidColorBrush x:Key="AccentBrush" Color="#4CC2FF" />
      </ResourceDictionary>
    </ResourceDictionary.ThemeDictionaries>
  </ResourceDictionary>
</Page.Resources>

<Border Background="{ThemeResource AccentBrush}" />

WinUI C#:

if (Application.Current.Resources.TryGetValue("AccentBrush", out var value) && value is SolidColorBrush brush)
{
    HeaderBorder.Background = brush;
}

Avalonia XAML:

<Application xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
  <Application.Resources>
    <ResourceDictionary>
      <ResourceDictionary.ThemeDictionaries>
        <ResourceDictionary x:Key="Light">
          <SolidColorBrush x:Key="AccentBrush" Color="#0063B1" />
        </ResourceDictionary>
        <ResourceDictionary x:Key="Dark">
          <SolidColorBrush x:Key="AccentBrush" Color="#4CC2FF" />
        </ResourceDictionary>
      </ResourceDictionary.ThemeDictionaries>
    </ResourceDictionary>
  </Application.Resources>
</Application>

<Border Background="{DynamicResource AccentBrush}" />

Avalonia C#:

if (Application.Current!.TryGetResource("AccentBrush", ThemeVariant.Dark, out var value) && value is IBrush brush)
{
    HeaderBorder.Background = brush;
}

Migration Notes

1. Translate ThemeResource usage to DynamicResource with explicit ThemeDictionaries keys.
2. Keep shared keys stable across light/dark dictionaries to prevent missing-resource fallbacks.
3. Validate lookup behavior at control scope and app scope after dictionary merge order changes.

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