主要機能：オフライン対応のデータフィード
オフライン永続化に対応したReact Queryでメインのデータフィードを構築し、プル・トゥ・リフレッシュとページネーションを実装します。作成・削除のミューテーションを追加し、リスト項目の表示をアニメーション化します。
「主要機能：オフライン対応のデータフィード」はCoddyKit上の無料React Native Academyレッスンです。 これはレッスン3/4です。 下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。 これはReact Native Academy学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 React Native Academyコースには全4レッスンが含まれています。
このレッスンの一部はまだ翻訳されておらず、英語で表示されています。
What Is Offline-First Design
Offline-first design means the app works correctly without an internet connection — users can view cached data, perform mutations that queue for sync, and experience no error messages just because the network is unavailable. Mobile users frequently move in and out of connectivity. A React Native app that breaks without a network feels fragile; one that keeps working feels polished and reliable.
Setting Up the QueryClient
React Query's QueryClient is the backbone of the data layer. Configure it with sensible defaults: a staleTime that avoids unnecessary refetches (e.g., 5 minutes for data that changes infrequently), and a gcTime (garbage collection time) that keeps unused data in the cache long enough to serve it from cache on reconnect. Pass this client to QueryClientProvider at the app root.
// src/services/queryClient.ts
import { QueryClient } from '@tanstack/react-query';
export const queryClient = new QueryClient({
defaultOptions: {
queries: {
staleTime: 1000 * 60 * 5, // 5 minutes — don't refetch too often
gcTime: 1000 * 60 * 60, // Keep in cache 1 hour after unmount
retry: 2,
retryDelay: (attempt) => Math.min(1000 * 2 ** attempt, 30000),
refetchOnWindowFocus: false, // Not needed on mobile
refetchOnReconnect: true, // Sync when network returns
},
},
});Persisting the Query Cache with AsyncStorage
To make data available when offline, persist the React Query cache to AsyncStorage. Use @tanstack/react-query-persist-client with an AsyncStorage persister. On app startup, the persisted cache is restored before the first network request — so users see their habits list immediately, even before the fetch completes. The cache is hydrated asynchronously, so show cached data optimistically and update when the fresh data arrives.
// App.tsx
import { PersistQueryClientProvider } from '@tanstack/react-query-persist-client';
import { createAsyncStoragePersister } from '@tanstack/query-async-storage-persister';
import AsyncStorage from '@react-native-async-storage/async-storage';
import { queryClient } from './src/services/queryClient';
const asyncStoragePersister = createAsyncStoragePersister({
storage: AsyncStorage,
key: 'REACT_QUERY_CACHE',
});
export default function App() {
return (
<PersistQueryClientProvider
client={queryClient}
persistOptions={{ persister: asyncStoragePersister }}
>
<AuthProvider>
<RootNavigator />
</AuthProvider>
</PersistQueryClientProvider>
);
}Fetching the Habits List with useQuery
Build a custom hook useHabits that encapsulates the Supabase query inside useQuery. The query key ['habits', userId] scopes the cache to the current user, preventing data from leaking between accounts. React Query returns data, isLoading, and error — pass all three to the screen to show the correct UI state at each point.
// src/hooks/useHabits.ts
import { useQuery } from '@tanstack/react-query';
import { supabase } from '../services/supabase';
import { useAuth } from '../context/AuthContext';
import { Habit } from '../types';
async function fetchHabits(userId: string): Promise<Habit[]> {
const { data, error } = await supabase
.from('habits')
.select('*')
.eq('user_id', userId)
.order('created_at', { ascending: true });
if (error) throw error;
return data;
}
export function useHabits() {
const { session } = useAuth();
const userId = session!.user.id;
return useQuery({
queryKey: ['habits', userId],
queryFn: () => fetchHabits(userId),
enabled: !!userId,
});
}Rendering the FlatList with Cached Data
Use the useHabits hook in the HabitList screen. Show a skeleton loader or spinner for the initial load, use the data array directly as the FlatList source, and handle the error state with a retry button. Because the cache is persisted, on subsequent app launches data is immediately available (no loading flash) while React Query fetches a fresh version in the background.
// src/screens/habits/HabitListScreen.tsx
import { FlatList, ActivityIndicator, View, Text } from 'react-native';
import { useHabits } from '../../hooks/useHabits';
import { HabitCard } from '../../components/HabitCard';
export function HabitListScreen() {
const { data: habits, isLoading, error, refetch } = useHabits();
if (isLoading && !habits) {
return <ActivityIndicator style={{ flex: 1 }} />;
}
if (error) {
return (
<View>
<Text>Failed to load habits.</Text>
<Button title='Retry' onPress={() => refetch()} />
</View>
);
}
return (
<FlatList
data={habits}
keyExtractor={(item) => item.id}
renderItem={({ item }) => <HabitCard habit={item} />}
onRefresh={refetch}
refreshing={isLoading}
/>
);
}Creating Habits with useMutation
useMutation handles the insert operation. On onSuccess, call queryClient.invalidateQueries(['habits', userId]) to trigger a fresh fetch of the habits list. This ensures the newly created habit appears in the list immediately after creation without manually updating the cache. Set onError to show the user an error message if the insert fails.
// src/hooks/useCreateHabit.ts
import { useMutation, useQueryClient } from '@tanstack/react-query';
import { supabase } from '../services/supabase';
import { useAuth } from '../context/AuthContext';
export function useCreateHabit() {
const queryClient = useQueryClient();
const { session } = useAuth();
const userId = session!.user.id;
return useMutation({
mutationFn: async ({ name, icon, color }) => {
const { error } = await supabase.from('habits').insert({
user_id: userId,
name,
icon,
color,
});
if (error) throw error;
},
onSuccess: () => {
queryClient.invalidateQueries({ queryKey: ['habits', userId] });
},
onError: (error) => {
Alert.alert('Error', error.message);
},
});
}Optimistic Updates for Check-In
For the daily check-in (marking a habit as done), use optimistic updates to update the UI instantly before the network request completes. When the user taps the check-in button, immediately update the cache with the assumed result. If the request fails, roll back the cache to the previous state. This makes the app feel instant even on slow networks.
// Optimistic update pattern with useMutation
const toggleCompletion = useMutation({
mutationFn: (habitId) => insertCompletion(habitId, today),
onMutate: async (habitId) => {
// Cancel in-flight refetches
await queryClient.cancelQueries({ queryKey: ['completions', userId] });
// Save snapshot for rollback
const previous = queryClient.getQueryData(['completions', userId]);
// Optimistically add completion
queryClient.setQueryData(['completions', userId], (old) => [
...old,
{ habit_id: habitId, completed_date: today }
]);
return { previous }; // Pass snapshot to onError
},
onError: (_err, _habitId, context) => {
// Roll back on failure
queryClient.setQueryData(['completions', userId], context.previous);
},
onSettled: () => {
queryClient.invalidateQueries({ queryKey: ['completions', userId] });
},
});Network Status and Offline Banner
Show users a subtle offline banner when the device has no internet connection so they understand why their changes haven't synced. Use @react-native-community/netinfo to listen for connectivity changes. React Query automatically pauses mutations when offline and retries them when connectivity returns — the banner simply makes this behavior visible to the user.
import NetInfo from '@react-native-community/netinfo';
import { useEffect, useState } from 'react';
export function OfflineBanner() {
const [isOffline, setIsOffline] = useState(false);
useEffect(() => {
const unsubscribe = NetInfo.addEventListener((state) => {
setIsOffline(!state.isConnected);
});
return unsubscribe;
}, []);
if (!isOffline) return null;
return (
<View style={{
backgroundColor: '#FF3B30',
padding: 8,
alignItems: 'center'
}}>
<Text style={{ color: 'white', fontWeight: 'bold' }}>
No internet connection — changes will sync when online
</Text>
</View>
);
}Pagination with FlatList and useInfiniteQuery
For feeds with many items, implement pagination using useInfiniteQuery. It fetches pages of data and appends them to a running list. Pass fetchNextPage to FlatList's onEndReached handler so the next page loads automatically as the user scrolls. Use getNextPageParam to derive the next page cursor from the last page's response.
import { useInfiniteQuery } from '@tanstack/react-query';
export function useHabitsPaginated() {
return useInfiniteQuery({
queryKey: ['habits', 'paginated'],
queryFn: ({ pageParam = 0 }) =>
supabase.from('habits').select('*')
.range(pageParam, pageParam + 19), // 20 per page
getNextPageParam: (lastPage, allPages) => {
const nextOffset = allPages.length * 20;
return lastPage.data?.length === 20 ? nextOffset : undefined;
},
initialPageParam: 0,
});
}
// In screen:
const { data, fetchNextPage, hasNextPage } = useHabitsPaginated();
const habits = data?.pages.flatMap(p => p.data) ?? [];
<FlatList
data={habits}
onEndReached={() => hasNextPage && fetchNextPage()}
onEndReachedThreshold={0.3}
/>Animating List Item Entry
Make the feed feel dynamic by animating items as they appear. A simple fade-in + slide-up on mount using the Animated API adds polish without heavy libraries. Create a reusable AnimatedListItem wrapper that each item passes through. The animation runs once on mount — use useRef to prevent re-triggering on re-renders.
import { useRef, useEffect } from 'react';
import { Animated } from 'react-native';
export function AnimatedListItem({ children, index }) {
const opacity = useRef(new Animated.Value(0)).current;
const translateY = useRef(new Animated.Value(20)).current;
useEffect(() => {
Animated.parallel([
Animated.timing(opacity, {
toValue: 1,
duration: 300,
delay: index * 50, // Stagger by index
useNativeDriver: true,
}),
Animated.timing(translateY, {
toValue: 0,
duration: 300,
delay: index * 50,
useNativeDriver: true,
}),
]).start();
}, []);
return (
<Animated.View style={{ opacity, transform: [{ translateY }] }}>
{children}
</Animated.View>
);
}Streak Calculation Logic
The streak is the number of consecutive days a habit was completed up to and including today. Calculate it in JavaScript from the completions array. Sort completions by date descending, start from today and walk backwards, counting consecutive days. This logic is pure JavaScript — no network call needed if the completions are already in the React Query cache.
// src/utils/streaks.ts
export function calculateStreak(completedDates: string[]): number {
if (completedDates.length === 0) return 0;
const sorted = [...completedDates].sort().reverse();
const today = new Date().toISOString().split('T')[0];
let streak = 0;
let current = new Date(today);
for (const dateStr of sorted) {
const expected = current.toISOString().split('T')[0];
if (dateStr === expected) {
streak++;
current.setDate(current.getDate() - 1);
} else if (dateStr < expected) {
break; // Gap found
}
}
return streak;
}
// Usage:
const streak = calculateStreak(
completions
.filter(c => c.habit_id === habit.id)
.map(c => c.completed_date)
);Quick Check
Test your understanding of React Native Mobile Development concepts from this lesson.
Lesson Recap
In this lesson you learned: how to configure React Query with persistence to serve cached data while offline, how to build custom hooks with useQuery and useMutation for habits CRUD, and how to implement optimistic updates for immediate UI feedback. You also saw how to add pagination, entry animations, and streak calculation from cached data. Next up we polish, test, and ship to both stores.
よくある質問
「主要機能：オフライン対応のデータフィード」レッスンは無料ですか？
はい。「主要機能：オフライン対応のデータフィード」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、React Native Academyコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 React Native Academyコースには全4レッスンが含まれています。
「主要機能：オフライン対応のデータフィード」で何を学びますか？
オフライン永続化に対応したReact Queryでメインのデータフィードを構築し、プル・トゥ・リフレッシュとページネーションを実装します。作成・削除のミューテーションを追加し、リスト項目の表示をアニメーション化します。 ブラウザで直接実行するハンズオンコードでReact Native Academyを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。
React Native Academyを始めるのに経験は必要ですか？
事前経験は必要ありません。CoddyKitのReact Native Academyは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。 これはレッスン3/4です。
「主要機能：オフライン対応のデータフィード」レッスンにはどのくらい時間がかかりますか？
ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。
このReact Native Academyレッスンでコードを書いて実行できますか？
はい。すべてのReact Native Academyレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。
このコースのすべてのレッスン
- アーキテクチャと技術スタックの計画
- 認証フローと保護されたルート
- 主要機能：オフライン対応のデータフィード
- 仕上げ、テスト、両ストアへの公開