54 lines
2.7 KiB
Markdown
54 lines
2.7 KiB
Markdown
---
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description: 'Performance requirements for data binding, layout, threading, and collection virtualization'
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applyTo: '**/*.cs, **/*.xaml'
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---
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# Performance
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These rules apply to **every feature and change**. They are not optional add-ons.
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---
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## Rules
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- **Use `x:Bind`** (compiled bindings) instead of `{Binding}` — it's faster and type-safe.
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- Use **`x:Load`** (or `x:DeferLoadStrategy`) to defer loading of UI elements not immediately visible.
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- Avoid heavy work on the UI thread — use `Task.Run` for CPU-bound work and `async/await` for I/O.
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- Use **virtualizing panels** (`ItemsRepeater` with `StackLayout`, or `ListView`) for long lists — never use `StackPanel` with hundreds of items.
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- **Cache** expensive computations and HTTP responses when appropriate.
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- Minimize XAML visual tree depth — deep nesting hurts layout performance.
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- Use **incremental loading** (`ISupportIncrementalLoading`) for large data sets.
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- Profile with **Visual Studio Diagnostics Tools** and **PerfView** before and after optimizations.
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- Be cautious with `DispatcherQueue.TryEnqueue` — don't flood the dispatcher queue.
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## Anti-patterns
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- Blocking the UI thread with `.Result` or `.GetAwaiter().GetResult()`.
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- Loading all data upfront when only a subset is needed.
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- Creating new `HttpClient` instances per request (use `IHttpClientFactory`).
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- Using `FindName()` or `VisualTreeHelper` in tight loops.
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## Validation
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- Build & register the MSIX package — see **Build, Run & Deploy** in `.github/agents/Agents.md`.
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### Verification Checklist
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- [ ] No blocking calls on the UI thread
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- [ ] `x:Bind` is used instead of `{Binding}`
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- [ ] Large lists use virtualization
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## Must Read & Research
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> **Agent Rule:** Before any performance-sensitive change (data binding, layout, collections, async), you **must** fetch and review these references using `fetch_webpage`. Apply what you learn.
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| # | Reference | When to consult |
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|---|---|---|
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| 1 | [Performance best practices for WinUI 3](https://learn.microsoft.com/en-us/windows/apps/performance/) | Any change touching UI rendering, data loading, or threading |
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| 2 | [x:Bind markup extension](https://learn.microsoft.com/en-us/windows/uwp/xaml-platform/x-bind-markup-extension) | Adding or modifying XAML data bindings |
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| 3 | [x:Load attribute](https://learn.microsoft.com/en-us/windows/uwp/xaml-platform/x-load-attribute) | Deferring UI element loading |
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| 4 | [Optimize XAML layout](https://learn.microsoft.com/en-us/windows/apps/performance/optimize-xaml-layout) | Restructuring XAML panels, reducing visual tree depth |
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| 5 | [ListView optimization](https://learn.microsoft.com/en-us/windows/apps/performance/optimize-listview) | Working with lists, collections, or `ItemsRepeater` |
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