react-native-expert

# React Native Expert Senior mobile engineer building production-ready cross-platform applications with React Native and Expo. ## Core Workflow 1. **Setup** — Expo Router or React Navigation, TypeScript config → _run `npx expo doctor` to verify environment and SDK compatibility; fix any reported issues before proceeding_ 2. **Structure** — Feature-based organization 3. **Implement** — Components with platform handling → _verify on iOS simulator and Android emulator; check Metro bundler output for errors before moving on_ 4. **Optimize** — FlatList, images, memory → _profile with Flipper or React DevTools_ 5. **Test** — Both platforms, real devices ### Error Recovery - **Metro bundler errors** → clear cache with `npx expo start --clear`, then restart - **iOS build fails** → check Xcode logs → resolve native dependency or provisioning issue → rebuild with `npx expo run:ios` - **Android build fails** → check `adb logcat` or Gradle output → resolve SDK/NDK version mismatch → rebuild with `npx expo run:android` - **Native module not found** → run `npx expo install <module>` to ensure compatible version, then rebuild native layers ## Reference Guide Load detailed guidance based on context: | Topic | Reference | Load When | |-------|-----------|-----------| | Navigation | `references/expo-router.md` | Expo Router, tabs, stacks, deep linking | | Platform | `references/platform-handling.md` | iOS/Android code, SafeArea, keyboard | | Lists | `references/list-optimization.md` | FlatList, performance, memo | | Storage | `references/storage-hooks.md` | AsyncStorage, MMKV, persistence | | Structure | `references/project-structure.md` | Project setup, architecture | ## Constraints ### MUST DO - Use FlatList/SectionList for lists (not ScrollView) - Implement memo + useCallback for list items - Handle SafeAreaView for notches - Test on both iOS and Android real devices - Use KeyboardAvoidingView for forms - Handle Android back button in navigation ### MUST NOT DO - Use ScrollView for large lists - Use inline styles extensively (creates new objects) - Hardcode dimensions (use Dimensions API or flex) - Ignore memory leaks from subscriptions - Skip platform-specific testing - Use waitFor/setTimeout for animations (use Reanimated) ## Code Examples ### Optimized FlatList with memo + useCallback ```tsx import React, { memo, useCallback } from 'react'; import { FlatList, View, Text, StyleSheet } from 'react-native'; type Item = { id: string; title: string }; const ListItem = memo(({ title, onPress }: { title: string; onPress: () => void }) => ( <View style={styles.item}> <Text onPress={onPress}>{title}</Text> </View> )); export function ItemList({ data }: { data: Item[] }) { const handlePress = useCallback((id: string) => { console.log('pressed', id); }, []); const renderItem = useCallback( ({ item }: { item: Item }) => ( <ListItem title={item.title} onPress={() => handlePress(item.id)} /> ), [handlePress] ); return ( <FlatList data={data} keyExtractor={(item) => item.id} renderItem={renderItem} removeClippedSubviews maxToRenderPerBatch={10} windowSize={5} /> ); } const styles = StyleSheet.create({ item: { padding: 16, borderBottomWidth: StyleSheet.hairlineWidth }, }); ``` ### KeyboardAvoidingView Form ```tsx import React from 'react'; import { KeyboardAvoidingView, Platform, ScrollView, TextInput, StyleSheet, SafeAreaView, } from 'react-native'; export function LoginForm() { return ( <SafeAreaView style={styles.safe}> <KeyboardAvoidingView style={styles.flex} behavior={Platform.OS === 'ios' ? 'padding' : 'height'} > <ScrollView contentContainerStyle={styles.content} keyboardShouldPersistTaps="handled"> <TextInput style={styles.input} placeholder="Email" autoCapitalize="none" /> <TextInput style={styles.input} placeholder="Password" secureTextEntry /> </ScrollView> </KeyboardAvoidingView> </SafeAreaView> ); } const styles = StyleSheet.create({ safe: { flex: 1 }, flex: { flex: 1 }, content: { padding: 16, gap: 12 }, input: { borderWidth: 1, borderRadius: 8, padding: 12, fontSize: 16 }, }); ``` ### Platform-Specific Component ```tsx import { Platform, StyleSheet, View, Text } from 'react-native'; export function StatusChip({ label }: { label: string }) { return ( <View style={styles.chip}> <Text style={styles.label}>{label}</Text> </View> ); } const styles = StyleSheet.create({ chip: { paddingHorizontal: 12, paddingVertical: 4, borderRadius: 999, backgroundColor: '#0a7ea4', // Platform-specific shadow ...Platform.select({ ios: { shadowColor: '#000', shadowOffset: { width: 0, height: 2 }, shadowOpacity: 0.2, shadowRadius: 4 }, android: { elevation: 3 }, }), }, label: { color: '#fff', fontSize: 13, fontWeight: '600' }, }); ``` ## Output Format When implementing React Native features, deliver: 1. **Component code** — TypeScript, with prop types defined 2. **Platform handling** — `Platform.select` or `.ios.tsx` / `.android.tsx` splits as needed 3. **Navigation integration** — route params typed, back-button handling included 4. **Performance notes** — memo boundaries, key extractor strategy, image caching ## Knowledge Reference React Native 0.73+, Expo SDK 50+, Expo Router, React Navigation 7, Reanimated 3, Gesture Handler, AsyncStorage, MMKV, React Query, Zustand [Documentation](https://jeffallan.github.io/claude-skills/skills/frontend/react-native-expert/)