WinUI 3 C# App

read other relevant winui* skills also as needed.

Workflow

1. Classify: new app, existing app, or specific issue.
2. New app → Quick Start (New). Existing app → Quick Start (Existing).
3. Route via Reference Index.

Core Rules

• Prefer Windows App SDK / WinUI APIs over custom interop.
• Code-behind = view glue only; state/logic in ViewModels.
• Prefer x:Bind (typed); Binding for dynamic DataContext.
• Marshal UI work through DispatcherQueue.
• System backdrops via Window.SystemBackdrop with fallback.
• Keep behavior stable unless explicitly asked to change.
• Architecture/packaging/library choices: present 2–3 options + tradeoffs + recommendation.

Scope

• In: WinUI 3 / Windows App SDK desktop apps, C#/XAML, MVVM, navigation, windowing, packaging, performance.
• Out: WPF, UWP, WinForms, C++/WinRT unless explicitly requested.

Reference Index

• references/foundations.md → project setup, release channels, MVVM/tooling, threading migration
• references/ui-ux.md → navigation, layout, title bar, backdrops, accessibility
• references/design-fluent.md → Fluent design principles, UX polish
• references/windowing.md → AppWindow, multi-window, dialogs, pickers
• references/performance.md → bindings, x:Load, list virtualization, perf basics

Quick Start (New)

1. Decide packaging + target framework; document constraints.
2. Architecture: code-behind for small apps, MVVM Toolkit for larger.
3. Create ViewModel, expose for x:Bind.
4. Layout with Grid/StackPanel.
5. Commands via RelayCommand/AsyncRelayCommand.
6. Add navigation if multi-page.

Quick Start (Existing)

1. Audit binding modes + DataContext; fix x:Bind vs Binding mismatches.
2. Move logic to ViewModels; keep code-behind thin.
3. Threading: UI updates on UI thread via DispatcherQueue.
4. Validate system backdrop usage + fallbacks.
5. Check dialogs, pickers, multi-window in references/windowing.md.