--- title: Building a Custom Checkbox: Avalonia UI Deep Dive description: Finishing off the Avalonia Checkbox — cleaning up duplication, locking in all visual states, and pushing further towards a unified theme system. No AI... canonical: https://daily.dev/posts/building-a-custom-checkbox-avalonia-ui-deep-dive-htrvhirjt twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Building a Custom Checkbox: Avalonia UI Deep Dive | daily.dev og:description: Finishing off the Avalonia Checkbox — cleaning up duplication, locking in all visual states, and pushing further towards a unified theme system. No AI... og:url: https://daily.dev/posts/building-a-custom-checkbox-avalonia-ui-deep-dive-htrvhirjt og:image: https://api.daily.dev/og/posts/HtrVhiRJt.png og:image:alt: Building a Custom Checkbox: Avalonia UI Deep Dive 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. # Building a Custom Checkbox: Avalonia UI Deep Dive **[AngelSix](https://daily.dev/sources/angelsix)** · 45 min read · 0 upvotes · 0 comments ## Summary Finishing off the Avalonia Checkbox — cleaning up duplication, locking in all visual states, and pushing further towards a unified theme system. No AI shortcuts, just real hand-coded engineering. We fix scaling, foreground pass-through, hover states, indeterminate styling, and more. This is part of a complete series on building a fully custom Avalonia UI theme from scratch, hand-coded with zero AI assistance. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 📌 WHAT YOU'LL LEARN ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ • How to centralise corner radius and stroke thickness as shared static resources • Correctly passing Foreground through TemplateBinding into child elements • Eliminating code duplication across checkbox states using the theme colour system • Applying numbered ThemeColor gradients for hover, pressed and disabled states • How ViewBox and RelativeSource binding fixes checkbox scaling when size changes • Styling all three checkbox states: Unchecked, Checked, and Indeterminate • Replacing the indeterminate "unknown panel" with a clean dedicated rectangle • Why style priority order matters and how to control which properties win ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ⏱ TIMESTAMPS ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ [0:00] – Introduction & recap — theme value sharing limitations [0:36] – Resuming checkbox styling & reviewing the stream geometry tick [2:35] – Main theme structure & TemplateBinding Foreground pass-through [2:57] – Introducing default corner radius & stroke thickness resources [6:57] – Code duplication problem & centralising theme colours [9:08] – Applying numbered ThemeColor gradients for visual states [13:31] – ViewBox revisited — Grid & Panel layout for tick scaling [16:16] – Hover (pointer over) state styling [21:10] – Checked state styling & style priority order [26:16] – Indeterminate state — replacing the unknown panel with a rectangle [40:40] – Fixing checkbox scaling with ViewBox & RelativeSource height-to-width binding [45:03] – Wrap up & next steps ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 🔗 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 📺 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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