React Native / Expo Patterns

Practical patterns for building production React Native apps with Expo. Covers navigation, state, data fetching, lists, styling, and native APIs. Pairs with the rules/react-native/ ruleset: rules say what to enforce, this skill shows how.

Libraries named below (NativeWind, Zustand/Jotai, TanStack Query) are common, well-established options shown for illustration — the patterns matter more than the specific package, and any equivalent works. Zod is used for validation to stay consistent with ECC's existing typescript/ rules.

These patterns assume the managed Expo workflow (Expo Router, EAS, expo-* modules) on the New Architecture (the default in recent Expo SDKs, mandatory from SDK 55+). They do NOT assume the browser DOM — React Native has no <div>, no URL bar, and no web data-fetching defaults.

When to Activate

Use this skill when:

• Building or editing React Native / Expo screens, components, or navigation
• Setting up routing with Expo Router (file-based app/ directory)
• Deciding where state belongs (server cache vs client store vs route params vs form)
• Wiring data fetching with TanStack Query and validating responses with Zod
• Rendering long or heavy lists
• Choosing or applying a styling approach (NativeWind or StyleSheet)
• Accessing native device APIs (camera, location, notifications) or secure storage
• Reviewing RN code for mobile-specific issues

Do NOT use the web/React-DOM patterns here — URL-as-state, <div>, and SWR-for-browser do not apply to React Native.

Core Concepts

Project structure (Expo Router)

File-based routing under app/. Keep route files thin: they read and validate params, then delegate to a screen component that lives in components/ or features/.

app/
  _layout.tsx          # root stack
  (tabs)/
    _layout.tsx        # tab navigator
    index.tsx          # Home
  user/[id].tsx        # dynamic route
components/
features/
  user/UserProfile.tsx

Navigation: validate route params

Deep links and dynamic routes deliver untrusted strings. Validate them with Zod before use.

// app/user/[id].tsx
import { useLocalSearchParams, router } from 'expo-router'
import { z } from 'zod'
import { UserProfile } from '@/features/user/UserProfile'

const Params = z.object({ id: z.string().uuid() })

export default function UserRoute() {
  const parsed = Params.safeParse(useLocalSearchParams())
  if (!parsed.success) {
    router.replace('/not-found')
    return null
  }
  return <UserProfile userId={parsed.data.id} />
}

State: keep concerns separate

Do not duplicate server data into a client store. Each concern has its own home.

Prefer local useState until state genuinely needs sharing.

Data fetching: a cache library + Zod

Use a server-cache library (TanStack Query, SWR) instead of fetch-in-useEffect. Validate at the boundary and infer types from the schema. Handle loading, error, and empty states explicitly. (Example uses TanStack Query.)

import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query'
import { z } from 'zod'

const User = z.object({ id: z.string(), email: z.string().email() })
type User = z.infer<typeof User>

export function useUser(id: string) {
  return useQuery({
    queryKey: ['user', id],
    queryFn: async (): Promise<User> => User.parse(await api.getUser(id)),
  })
}

export function useUpdateEmail(id: string) {
  const qc = useQueryClient()
  return useMutation({
    mutationFn: (email: string) => api.updateEmail(id, email),
    onSuccess: () => qc.invalidateQueries({ queryKey: ['user', id] }),
  })
}

Lists: virtualize, never map a big array in a ScrollView

import { FlatList } from 'react-native'

<FlatList
  data={items}
  keyExtractor={(item) => item.id}
  renderItem={renderItem}          // memoized
  initialNumToRender={10}
  windowSize={5}
/>

Use FlashList (Shopify) for large or heterogeneous lists.

Styling: pick one system

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