Uploaded July 2022 | Updated September 2026, 3 weeks ago
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Avalonia UI
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Support me in my journey to giving back to the industry all my knowledge and helping the world with what I do. Spreading knowledge to those who cannot afford an education, and helping those who want to better themselves.
Avalonia UI
avaloniaui.net
Support what I do and pay for me to survive
angelsix.com/donate
Live Chat at Discord
discordapp.com/invite/eHr5BMk

![Avalonia UI Theming - Theme Engine From Scratch | No AI
Avalonia has never had a proper theme engine — until now. After a full week of deep refactoring, Ive 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.
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📌 WHAT YOULL LEARN
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• 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
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⏱ TIMESTAMPS
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[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 wasnt 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 & whats next
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🔗 LINKS
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▶ 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
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📺 SERIES: Avalonia UI Theming – Hand Coded From Scratch
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#avalonia #avaloniaui #xaml #csharp #dotnet #uiux #desktopapp #softwaretutorial #coding Avalonia UI Theming - Theme Engine From Scratch | No AI](https://i.ytimg.com/vi/NXz8hwITg5U/mqdefault.jpg)


![Avalonia Styles Not Working? Youre Breaking This Rule
Your Avalonia styles write correctly, apply cleanly — and do absolutely nothing. No error.
No warning. Just silence. This is what happens when one rule gets broken inside a Control
Template, and it took a deep dive into Avalonias full binding precedence order to understand
why.
In this episode were finishing the Button Spinner styling — but the real story is discovering
that a single Binding inside the default control template was silently blocking every style
override we tried to write. We dig into the full priority order, document it properly, and
rebuild the Button Spinner cleanly from there.
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📌 WHAT YOULL LEARN
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• Avalonias full binding precedence order — Animation → Local Value → Style Trigger →
TemplateBinding → Style Setter → Inherited → Default
• The rule you must never break inside a Control Template — and what silently breaks when
you do
• Why using a regular Binding inside a Control Template blocks all style overrides forever
• How to fix it: moving the offending property to a Style Setter instead
• Cleaning up duplicate stream geometries — replacing two separate paths with a single arrow
and RenderTransform
• Removing all hardcoded MinWidth, padding, and icon sizes — wiring everything through the
token system
• A new binding priority reference document, available on GitHub
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⏱ TIMESTAMPS
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[0:00] – Introduction & series progress overview
[3:00] – Reviewing the Button Spinner control template
[7:02] – Cleaning up the Repeat Button control theme
[10:39] – Margin Multiplier Converter & Stream Geometry tasks
[14:36] – Removing the unnecessary control theme
[17:25] – The rule you must never break inside a Control Template
[18:00] – Avalonias binding precedence order, explained
[19:31] – The binding priority reference document
[22:52] – Reviewing the cleaned-up styles
[24:57] – Final cleanup: padding, paths, and icon sizing
[29:48] – Wrap-up
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🔗 LINKS
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▶ Ep 1 – Setup: https://www.youtube.com/watch?v=rUKlQnjU0tc
▶ Ep 2 – Buttons: https://www.youtube.com/watch?v=oKjk6pyyARI
▶ Ep 3 – Button Spinner Anatomy: https://www.youtube.com/watch?v=WMaTbXkvm9g
▶ Ep 4 – Designing a Theme System: https://www.youtube.com/watch?v=I5halHoNfH0
▶ Ep 5 – Checkbox Deep Dive: https://www.youtube.com/watch?v=uIimnwjITT0
▶ Ep 6 – Checkbox Styling: https://www.youtube.com/watch?v=uv1bNrfCjtY
▶ Ep 7 – Theme Engine From Scratch: https://www.youtube.com/watch?v=NXz8hwITg5U
▶ Ep 8 – Design Token System: https://www.youtube.com/watch?v=QMVdxRZqaU8
▶ Ep 9 – Surgical Legacy Code Removal: https://www.youtube.com/watch?v=5-p_fnOi0As
▶ Ep 10 – One Token System: https://www.youtube.com/watch?v=JEcD1XXIiA8
📺 Full Series Playlist: https://www.youtube.com/playlist?list=PLrW43fNmjaQVE2vDBeWD8QYIm06w6bKyO
💾 Source Code & Binding Priority Doc: https://github.com/angelsix/youtube/tree/develop/AvaloniaThemeLab
🌐 AngelSix: https://www.angelsix.com
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📺 SERIES: Avalonia UI Theming – Hand Coded From Scratch
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#avalonia #avaloniaui #xaml #csharp #dotnet #uiux #desktopapp #softwaretutorial #coding Avalonia Styles Not Working? Youre Breaking This Rule](https://i.ytimg.com/vi/OhJN8Ssp2hA/mqdefault.jpg)





