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React Native Academy · Aula

Recurso principal: feed de dados com suporte offline

Crie o feed principal de dados usando React Query com persistência offline, implemente atualização por gesto de puxar e paginação, adicione mutações de criação e exclusão e anime a entrada dos itens da lista.

Recurso principal: feed de dados com suporte offline é uma aula grátis de React Native Academy no CoddyKit. Esta é a aula 3 de 4. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de React Native Academy, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de React Native Academy inclui 4 aulas no total.

Partes desta aula ainda não foram traduzidas e aparecem em inglês.

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.

Perguntas Frequentes

A aula “Recurso principal: feed de dados com suporte offline” é grátis?

Sim — o texto completo de “Recurso principal: feed de dados com suporte offline” é grátis para ler aqui na web. Para praticá-la interativamente (um editor de código integrado e um tutor de IA 24/7) e desbloquear o restante do curso de React Native Academy, atualize para CoddyKit PRO. O curso de React Native Academy inclui 4 aulas no total.

O que vou aprender em “Recurso principal: feed de dados com suporte offline”?

Crie o feed principal de dados usando React Query com persistência offline, implemente atualização por gesto de puxar e paginação, adicione mutações de criação e exclusão e anime a entrada dos itens… Você pratica React Native Academy com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.

Preciso ter experiência prévia para começar React Native Academy?

Nenhuma experiência prévia é necessária. React Native Academy no CoddyKit é estruturado para alunos iniciantes até avançados, então você pode começar aqui ou desde o início e aprender no seu ritmo. Esta é a aula 3 de 4.

Quanto tempo leva a aula “Recurso principal: feed de dados com suporte offline”?

A maioria das aulas CoddyKit leva cerca de 5–10 minutos. Cada uma é compacta e interativa, então você faz progresso constante e retoma exatamente de onde parou entre web e app.

Posso escrever e executar código nesta aula de React Native Academy?

Sim. Cada aula de React Native Academy inclui um editor de código integrado, então você escreve e executa código real direto no navegador e recebe feedback de IA instantaneamente — nenhuma configuração local necessária.

Todas as aulas deste curso

  1. Planejando a arquitetura e a stack tecnológica
  2. Fluxo de autenticação e rotas protegidas
  3. Recurso principal: feed de dados com suporte offline
  4. Acabamento, testes e publicação nas duas lojas
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