--- title: Avalonia UI Theming - Theme Engine From Scratch | No AI description: Avalonia has never had a proper theme engine — until now. After a full week of deep refactoring, I've designed and built a brand new C#-driven theme engine... canonical: https://daily.dev/posts/avalonia-ui-theming---theme-engine-from-scratch-no-ai-ygenznifb twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Avalonia UI Theming - Theme Engine From Scratch | No AI | daily.dev og:description: Avalonia has never had a proper theme engine — until now. After a full week of deep refactoring, I've designed and built a brand new C#-driven theme engine... og:url: https://daily.dev/posts/avalonia-ui-theming---theme-engine-from-scratch-no-ai-ygenznifb og:image: https://api.daily.dev/og/posts/YgeNzNifb.png og:image:alt: Avalonia UI Theming - Theme Engine From Scratch | No AI og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Avalonia UI Theming - Theme Engine From Scratch | No AI **[AngelSix](https://daily.dev/sources/angelsix)** · 21 min read · 0 upvotes · 0 comments ## Summary Avalonia has never had a proper theme engine — until now. After a full week of deep refactoring, I've designed and built a brand new C#-driven theme engine that replaces static XAML resource dictionaries with dynamic, MVVM-bound, fully IntelliSense-supported theme properties. No AI wrote this. A real person architected every piece. This is the biggest leap forward in the series so far. The entire theming system has been reduced to just two classes and a NuGet package — and it gives you absolute power over your themes: live switching, data-bound values, even themes that react to external events in real-time. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 📌 WHAT YOU'LL LEARN ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ • Why defining themes in XAML is fundamentally limiting — and the case for C# instead • How current Avalonia theming fails: hard-coded values, no IntelliSense, no binding • The dead ends I hit (including why modifying XAMLX was a non-starter) • The breakthrough: markup extensions as the entry point for theme:PropertyName syntax • Full IntelliSense for every theme property directly in XAML • ThemeContext — a singleton injected via DI that holds the active theme • Themes as simple C# classes inheriting from an abstract Theme base • Live theme switching: toggle themes at runtime and watch the UI update instantly • Binding theme values to external data — including a demo where BaseScale changes every second from the system clock • Auto-generated C# files that power the IntelliSense and markup resolution ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ⏱ TIMESTAMPS ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ [0:00] – Introduction — a week of redesigning the theme system [2:29] – Why XAML is the wrong place to define themes [4:50] – The XAMLX dead end — why patching the compiler wasn't viable [7:24] – The breakthrough: markup extensions & the new architecture [9:15] – ThemeContext, dependency injection & the singleton pattern [10:30] – Themes as C# classes — inheriting from abstract Theme [12:02] – Full IntelliSense demo for theme: syntax in XAML [13:45] – Live theme switching — toggling themes at runtime [15:20] – Binding ThemeContext in XAML & the single naming requirement [16:10] – How auto-generated files power the system behind the scenes [20:00] – The crazy demo: BaseScale driven by the system clock [21:07] – Wrap up & what's next ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 🔗 LINKS ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ▶ Part 1 – Setup: https://www.youtube.com/watch?v=rUKlQnjU0tc ▶ Part 2 – Buttons: https://www.youtube.com/watch?v=oKjk6pyyARI ▶ Part 3 – Button Spinner Anatomy: https://www.youtube.com/watch?v=WMaTbXkvm9g ▶ Part 4 – Designing a Theme System: https://www.youtube.com/watch?v=I5halHoNfH0 ▶ Part 5 – Checkbox Anatomy: https://www.youtube.com/watch?v=uIimnwjITT0 ▶ Part 6 – Checkbox Styling: https://www.youtube.com/watch?v=uv1bNrfCjtY 📺 Full Series Playlist: https://www.youtube.com/playlist?list=PLrW43fNmjaQVE2vDBeWD8QYIm06w6bKyO 💾 Source Code: https://github.com/angelsix/youtube/tree/develop/AvaloniaThemeLab 🌐 AngelSix: https://www.angelsix.com ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 📺 SERIES: Avalonia UI Theming – Hand Coded From Scratch ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ #avalonia #avaloniaui #xaml #csharp #dotnet #uiux #desktopapp #softwaretutorial #coding ## Full article daily.dev links to this article rather than hosting it. 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