playbook/antigravity-awesome-skills/skills/expo-ui/references/jetpack-compose.md

Platform-specific Android UI: @expo/ui/jetpack-compose

Android only. Code that imports from @expo/ui/jetpack-compose will crash on iOS with "Unable to get view config" errors. Always place this code in an .android.tsx component file or guard it with Platform.OS === 'android'. Host must be imported from @expo/ui (the universal root), not from @expo/ui/jetpack-compose.

Use this layer only when the universal @expo/ui components don't cover what you need on Android (see ./universal.md first). This requires a platform-specific tree.

File placement with Expo Router

Do not put .android.tsx files inside app/ or src/app/. Expo Router does not support platform-extension suffixes for route files and will throw a "no fallback sibling" Render Error.

Place platform-specific component files in components/ (or any directory outside the route tree), then import them from a regular route file:

src/components/ProductList.android.tsx   ← Compose tree lives here
src/app/product-list.tsx                 ← regular Expo Router route, imports the component

src/app/product-list.tsx:

import ProductList from '../components/ProductList';
export default ProductList;

Alternatively, keep everything in one regular route file and branch on Platform.OS:

// src/app/product-list.tsx
import { Platform } from 'react-native';
const ComposeList = Platform.OS === 'android' ? require('../components/ProductList.android').default : null;

Instructions

• Expo UI's API mirrors Jetpack Compose's API. Use Jetpack Compose and Material Design 3 knowledge to decide which components or modifiers to use. If you need deeper Jetpack Compose or Material 3 guidance (e.g. which component to pick, layout patterns, theming), spawn a subagent to research Jetpack Compose and Material Design 3 best practices.
• Components are imported from @expo/ui/jetpack-compose, modifiers from @expo/ui/jetpack-compose/modifiers.
• Before writing any code, run the list-components script to get the exact components and modifiers available in the installed version:

  node <skill-root>/scripts/list-components.js <project-path>          # names only (compact)
  node <skill-root>/scripts/list-components.js <project-path> --docs   # with one-line descriptions
  

  (<skill-root> is the directory containing this references/ folder.)
• Always read the .d.ts type files to confirm prop shapes and signatures — read the relevant {ComponentName}/index.d.ts from the installed @expo/ui/jetpack-compose package in node_modules. This is the most reliable source of truth.
• When about to use a component, fetch its docs to confirm the API — https://docs.expo.dev/versions/latest/sdk/ui/jetpack-compose/{component-name}/index.md
• When unsure about a modifier's API, refer to the docs — https://docs.expo.dev/versions/latest/sdk/ui/jetpack-compose/modifiers/index.md
• Every Jetpack Compose tree must be wrapped in Host. Use <Host matchContents> for intrinsic sizing, or <Host style={{ flex: 1 }}> when you need explicit size (e.g. as a parent of LazyColumn). Example:

import { Host } from "@expo/ui";                              // Host always from universal root
import { Column, Button, Text } from "@expo/ui/jetpack-compose";
import { fillMaxWidth, paddingAll } from "@expo/ui/jetpack-compose/modifiers";

<Host matchContents>
  <Column verticalArrangement={{ spacedBy: 8 }} modifiers={[fillMaxWidth(), paddingAll(16)]}>
    <Text style={{ typography: "titleLarge" }}>Hello</Text>
    <Button onPress={() => alert("Pressed!")}>Press me</Button>
  </Column>
</Host>;

• RNHostView embeds React Native components inside a Jetpack Compose tree (the same concept as in @expo/ui/swift-ui) — wrap any RN child in <RNHostView>.
• If a required composable or modifier is missing in Expo UI, it can be extended via a local Expo module. See: https://docs.expo.dev/guides/expo-ui-jetpack-compose/extending/index.md. Confirm with the user before extending.

Key Components

• LazyColumn — Use instead of react-native ScrollView/FlatList for scrollable lists. Wrap in <Host style={{ flex: 1 }}>. Not suitable for large lists — each item is a JSX node processed on the JS thread, which causes noticeable slowdowns at scale.
• Icon — Use <Icon source={require('./icon.xml')} size={24} /> with Android XML vector drawables. To get icons: go to Material Symbols, select an icon, choose the Android platform, and download the XML vector drawable. Save these as .xml files in your project's assets/ directory (e.g. assets/icons/wifi.xml). Metro bundles .xml assets automatically — no metro config changes needed.

useNativeState

useNativeState creates observable state that updates synchronously on the UI thread via worklets, enabling immediate native state changes without waiting for a React render cycle. Requires react-native-worklets — without it updates still go through React and flickering remains. Best for real-time interactions where synchronous updates matter, e.g. a text field that masks or formats input as the user types.

• ObservableState.value is readable/writable from worklets; onChange fires a worklet listener on state change.
• Docs — https://docs.expo.dev/versions/latest/sdk/ui/jetpack-compose/usenativestate/index.md