React Native Architecture

# react-native-architecture — detailed patterns and worked examples

## Patterns

### Pattern 1: Expo Router Navigation

```typescript
// app/(tabs)/_layout.tsx
import { Tabs } from 'expo-router'
import { Home, Search, User, Settings } from 'lucide-react-native'
import { useTheme } from '@/hooks/useTheme'

export default function TabLayout() {
  const { colors } = useTheme()

  return (
    <Tabs
      screenOptions={{
        tabBarActiveTintColor: colors.primary,
        tabBarInactiveTintColor: colors.textMuted,
        tabBarStyle: { backgroundColor: colors.background },
        headerShown: false,
      }}
    >
      <Tabs.Screen
        name="index"
        options={{
          title: 'Home',
          tabBarIcon: ({ color, size }) => <Home size={size} color={color} />,
        }}
      />
      <Tabs.Screen
        name="search"
        options={{
          title: 'Search',
          tabBarIcon: ({ color, size }) => <Search size={size} color={color} />,
        }}
      />
      <Tabs.Screen
        name="profile"
        options={{
          title: 'Profile',
          tabBarIcon: ({ color, size }) => <User size={size} color={color} />,
        }}
      />
      <Tabs.Screen
        name="settings"
        options={{
          title: 'Settings',
          tabBarIcon: ({ color, size }) => <Settings size={size} color={color} />,
        }}
      />
    </Tabs>
  )
}

// app/(tabs)/profile/[id].tsx - Dynamic route
import { useLocalSearchParams } from 'expo-router'

export default function ProfileScreen() {
  const { id } = useLocalSearchParams<{ id: string }>()

  return <UserProfile userId={id} />
}

// Navigation from anywhere
import { router } from 'expo-router'

// Programmatic navigation
router.push('/profile/123')
router.replace('/login')
router.back()

// With params
router.push({
  pathname: '/product/[id]',
  params: { id: '123', referrer: 'home' },
})
```

### Pattern 2: Authentication Flow

```typescript
// providers/AuthProvider.tsx
import { createContext, useContext, useEffect, useState } from 'react'
import { useRouter, useSegments } from 'expo-router'
import * as SecureStore from 'expo-secure-store'

interface AuthContextType {
  user: User | null
  isLoading: boolean
  signIn: (credentials: Credentials) => Promise<void>
  signOut: () => Promise<void>
}

const AuthContext = createContext<AuthContextType | null>(null)

export function AuthProvider({ children }: { children: React.ReactNode }) {
  const [user, setUser] = useState<User | null>(null)
  const [isLoading, setIsLoading] = useState(true)
  const segments = useSegments()
  const router = useRouter()

  // Check authentication on mount
  useEffect(() => {
    checkAuth()
  }, [])

  // Protect routes
  useEffect(() => {
    if (isLoading) return

    const inAuthGroup = segments[0] === '(auth)'

    if (!user && !inAuthGroup) {
      router.replace('/login')
    } else if (user && inAuthGroup) {
      router.replace('/(tabs)')
    }
  }, [user, segments, isLoading])

  async function checkAuth() {
    try {
      const token = await SecureStore.getItemAsync('authToken')
      if (token) {
        const userData = await api.getUser(token)
        setUser(userData)
      }
    } catch (error) {
      await SecureStore.deleteItemAsync('authToken')
    } finally {
      setIsLoading(false)
    }
  }

  async function signIn(credentials: Credentials) {
    const { token, user } = await api.login(credentials)
    await SecureStore.setItemAsync('authToken', token)
    setUser(user)
  }

  async function signOut() {
    await SecureStore.deleteItemAsync('authToken')
    setUser(null)
  }

  if (isLoading) {
    return <SplashScreen />
  }

  return (
    <AuthContext.Provider value={{ user, isLoading, signIn, signOut }}>
      {children}
    </AuthContext.Provider>
  )
}

export const useAuth = () => {
  const context = useContext(AuthContext)
  if (!context) throw new Error('useAuth must be used within AuthProvider')
  return context
}
```

### Pattern 3: O