# Building Native UI

> Complete guide for building beautiful apps with Expo Router. Covers fundamentals, styling, components, navigation, animations, patterns, and native tabs.

- Skill: `ranbot-ai/building-native-ui` (Agent Skill)
- Install (CLI): `npx skillmds add ranbot-ai/building-native-ui`
- Raw SKILL.md: https://api.skillmd.com/api/skills/ranbot-ai/building-native-ui/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: ranbot-ai (https://skillmd.com/u/ranbot-ai)
- Updated: 2026-09-08
- Page: https://skillmd.com/skills/ranbot-ai/building-native-ui

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# Expo UI Guidelines
## When to Use

Use this skill when you need complete guide for building beautiful apps with Expo Router. Covers fundamentals, styling, components, navigation, animations, patterns, and native tabs.


## References

Consult these resources as needed:

```
references/
  animations.md          Reanimated: entering, exiting, layout, scroll-driven, gestures
  controls.md            Native iOS: Switch, Slider, SegmentedControl, DateTimePicker, Picker
  form-sheet.md          Form sheets in expo-router: configuration, footers and background interaction.
  gradients.md           CSS gradients via experimental_backgroundImage (New Arch only)
  icons.md               SF Symbols via expo-image (sf: source), names, animations, weights
  media.md               Camera, audio, video, and file saving
  route-structure.md     Route conventions, dynamic routes, groups, folder organization
  search.md              Search bar with headers, useSearch hook, filtering patterns
  storage.md             SQLite, AsyncStorage, SecureStore
  tabs.md                NativeTabs, migration from JS tabs, iOS 26 features
  toolbar-and-headers.md Stack headers and toolbar buttons, menus, search (iOS only)
  visual-effects.md      Blur (expo-blur) and liquid glass (expo-glass-effect)
  webgpu-three.md        3D graphics, games, GPU visualizations with WebGPU and Three.js
  zoom-transitions.md    Apple Zoom: fluid zoom transitions with Link.AppleZoom (iOS 18+)
```

## Running the App

**CRITICAL: Always try Expo Go first before creating custom builds.**

Most Expo apps work in Expo Go without any custom native code. Before running `npx expo run:ios` or `npx expo run:android`:

1. **Start with Expo Go**: Run `npx expo start` and scan the QR code with Expo Go
2. **Check if features work**: Test your app thoroughly in Expo Go
3. **Only create custom builds when required** - see below

### When Custom Builds Are Required

You need `npx expo run:ios/android` or `eas build` ONLY when using:

- **Local Expo modules** (custom native code in `modules/`)
- **Apple targets** (widgets, app clips, extensions via `@bacons/apple-targets`)
- **Third-party native modules** not included in Expo Go
- **Custom native configuration** that can't be expressed in `app.json`

### When Expo Go Works

Expo Go supports a huge range of features out of the box:

- All `expo-*` packages (camera, location, notifications, etc.)
- Expo Router navigation
- Most UI libraries (reanimated, gesture handler, etc.)
- Push notifications, deep links, and more

**If you're unsure, try Expo Go first.** Creating custom builds adds complexity, slower iteration, and requires Xcode/Android Studio setup.

## Code Style

- Be cautious of unterminated strings. Ensure nested backticks are escaped; never forget to escape quotes correctly.
- Always use import statements at the top of the file.
- Always use kebab-case for file names, e.g. `comment-card.tsx`
- Always remove old route files when moving or restructuring navigation
- Never use special characters in file names
- Configure tsconfig.json with path aliases, and prefer aliases over relative imports for refactors.

## Routes

See `./references/route-structure.md` for detailed route conventions.

- Routes belong in the `app` directory.
- Never co-locate components, types, or utilities in the app directory. This is an anti-pattern.
- Ensure the app always has a route that matches "/", it may be inside a group route.

## Library Preferences

- Never use modules removed from React Native such as Picker, WebView, SafeAreaView, or AsyncStorage
- Never use legacy expo-permissions
- `expo-audio` not `expo-av`
- `expo-video` not `expo-av`
- `expo-image` with `source="sf:name"` for SF Symbols, not `expo-symbols` or `@expo/vector-icons`
- `react-native-safe-area-context` not react-native SafeAreaView
- `process.env.EXPO_OS` not `Platform.OS`
- `React.use` not `React.useContext`
- `expo-image` Image component instead of intrinsic element `img`
- `expo-glass-effect` for liquid glass backdrops
- `Color` from `expo-router` for native semantic colors, not raw `PlatformColor` (type-safe, auto-adapts to light/dark)
- In SDK 56+, never import from `@react-navigation/*` directly — use `expo-router/react-navigation` instead (covers `@react-navigation/native`, `/core`, `/elements`, `/routers`)

## Responsiveness

- Always wrap root component in a scroll view for responsiveness
- Use `<ScrollView contentInsetAdjustmentBehavior="automatic" />` instead of `<SafeAreaView>` for smarter safe area insets
- `contentInsetAdjustmentBehavior="automatic"` should be applied to FlatList and SectionList as well
- Use flexbox instead of Dimensions API
- ALWAYS prefer `useWindowDimensions` over `Dimensions.get()` to measure screen size

## Behavior

- Use expo-haptics conditionally on iOS to make more delightful experiences
- Use views with built-in haptics like `<Switch />` from React Native and `@react-native-community/datetimepicker`
- When a route belon