xaml-csharp-development-skill-for-avalonia

WinUI Style Resolution (BasedOn/Implicit) to Avalonia Selectors

Table of Contents

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

Scope and APIs

Primary WinUI APIs:

• Style, Setter, BasedOn, TargetType
• implicit style by TargetType, explicit style by x:Key

Primary Avalonia APIs:

• Style + selector syntax
• classes and pseudo-classes
• ControlTheme, StyledElement.Theme, StyleKeyOverride

Concept Mapping

WinUI idiom	Avalonia idiom
implicit style by control type	type selector (Button)
explicit style key usage	style/class/theme indirection
stateful style in visual states	selector + pseudo-class (:pointerover, :pressed)
BasedOn style chains	selector layering and ControlTheme.BasedOn

Conversion Example

WinUI XAML:

<Page.Resources>
  <Style x:Key="AccentButtonStyle"
         TargetType="Button"
         BasedOn="{StaticResource DefaultButtonStyle}">
    <Setter Property="Background" Value="{ThemeResource AccentFillColorDefaultBrush}" />
  </Style>
</Page.Resources>

<Button Style="{StaticResource AccentButtonStyle}" Content="Save" />

WinUI C#:

SaveButton.Style = (Style)Application.Current.Resources["AccentButtonStyle"];

Avalonia XAML:

<Styles xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
  <Style Selector="Button.accent">
    <Setter Property="Background" Value="{DynamicResource AccentBrush}" />
  </Style>

  <Style Selector="Button.accent:pointerover">
    <Setter Property="Opacity" Value="0.92" />
  </Style>
</Styles>

<Button Classes="accent" Content="Save" />

Avalonia C#:

SaveButton.Classes.Add("accent");

Migration Notes

1. Convert key-based style selection to selector/class-driven selection where possible.
2. Keep selector specificity shallow; prefer explicit classes over deeply nested selectors.
3. Use ControlTheme when template-level reuse is required, not only simple property overrides.

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