React Native Academy · レッスン

コンポーネントでのStore Stateの読み取りと更新

useStoreフックを使ってReact Nativeコンポーネントからstoreの値とアクションにアクセスし、ボタン操作やフォーム送信から更新を実行します

「コンポーネントでのStore Stateの読み取りと更新」はCoddyKit上の無料React Native Academyレッスンです。これはレッスン2/4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。

Connecting a Component to Zustand

Using a Zustand store in a component is as simple as calling the store hook at the top of the function. The hook is the same object returned by create. You can pass a selector to pick specific values, or read actions directly. No import of useSelector or useDispatch is required — the store hook handles everything.

import { useCounterStore } from '../stores/counterStore';

export default function CounterScreen() {
  const count = useCounterStore((state) => state.count);
  const increment = useCounterStore((state) => state.increment);
  const decrement = useCounterStore((state) => state.decrement);

  return (
    <View style={styles.container}>
      <Text style={styles.count}>{count}</Text>
      <Button title='Increment' onPress={increment} />
      <Button title='Decrement' onPress={decrement} />
    </View>
  );
}

Selecting Multiple Values Efficiently

To read multiple values from a Zustand store without causing excessive re-renders, you have two options. You can call the store hook multiple times with individual selectors (each subscription is independent), or you can return an object and use the shallow equality helper to compare each property separately.

import { shallow } from 'zustand/shallow';

// Option 1: multiple hooks (preferred for 2-3 values)
const count = useCounterStore((s) => s.count);
const status = useCounterStore((s) => s.status);

// Option 2: shallow equality for multiple values at once
const { count, status } = useCounterStore(
  (s) => ({ count: s.count, status: s.status }),
  shallow
);

Triggering Updates from Button Presses

Zustand actions are plain JavaScript functions, so you pass them directly to React Native event handlers like onPress. You do not need to dispatch an action object or call a helper — just call the function. This makes the component code cleaner and easier to read compared to the Redux dispatch pattern.

export default function TodoInput() {
  const [text, setText] = React.useState('');
  const addTodo = useTodoStore((state) => state.addTodo);

  const handleAdd = () => {
    if (text.trim()) {
      addTodo(text.trim());
      setText('');
    }
  };

  return (
    <View>
      <TextInput value={text} onChangeText={setText} placeholder='New todo' />
      <Button title='Add' onPress={handleAdd} />
    </View>
  );
}

Reading Store State in a FlatList

Zustand stores work naturally with React Native's FlatList. Select the array from the store and pass it to the data prop. Zustand only re-renders this component when the array reference changes, which happens when your store action replaces or mutates the items array and returns a new reference via set.

export default function TodoList() {
  const todos = useTodoStore((state) => state.todos);
  const removeTodo = useTodoStore((state) => state.removeTodo);

  return (
    <FlatList
      data={todos}
      keyExtractor={(item) => item.id}
      renderItem={({ item }) => (
        <TouchableOpacity onPress={() => removeTodo(item.id)}>
          <Text>{item.text}</Text>
        </TouchableOpacity>
      )}
    />
  );
}

Updating Nested State

When your store state has nested objects, pass a function to set and spread the nested level you want to update. Without spreading, set would replace the top-level key entirely, wiping out other nested properties. Alternatively, use the Immer middleware (covered in the previous lesson) to mutate nested values directly.

export const useProfileStore = create<ProfileStore>((set) => ({
  profile: {
    name: '',
    bio: '',
    avatar: null,
  },
  updateName: (name: string) =>
    set((state) => ({ profile: { ...state.profile, name } })),
  updateBio: (bio: string) =>
    set((state) => ({ profile: { ...state.profile, bio } })),
}));

Optimistic UI Updates

Optimistic updates improve perceived performance by updating the UI immediately when the user takes an action, before waiting for the server response. In Zustand, call set to update state immediately, then make the API call. If the API fails, call set again to revert the state to its previous value.

toggleLike: async (postId: string) => {
  // Update UI immediately
  set((state) => ({
    posts: state.posts.map((p) =>
      p.id === postId ? { ...p, liked: !p.liked } : p
    ),
  }));
  try {
    await api.toggleLike(postId);
  } catch {
    // Revert on failure
    set((state) => ({
      posts: state.posts.map((p) =>
        p.id === postId ? { ...p, liked: !p.liked } : p
      ),
    }));
  }
}

Resetting Store State

A common pattern is to add a reset action that restores the store to its initial state. Store the initial state in a constant outside the create call and reference it in the reset action. This is useful for logout flows where you need to clear all user data from every store at once.

const initialState = { user: null, token: null, isLoggedIn: false };

export const useAuthStore = create<AuthStore>((set) => ({
  ...initialState,
  login: (user, token) => set({ user, token, isLoggedIn: true }),
  logout: () => set(initialState), // restore all fields to initial values
}));

Watching Store Changes with subscribe

useStore.subscribe lets you react to store changes outside of React components — for example, writing to AsyncStorage whenever settings change, or logging analytics events when specific state transitions occur. Always unsubscribe in the cleanup function to avoid memory leaks.

useEffect(() => {
  const unsubscribe = useSettingsStore.subscribe(
    (state) => state.theme,
    (theme) => {
      console.log('Theme changed to:', theme);
      AsyncStorage.setItem('theme', theme);
    }
  );
  return unsubscribe; // cleanup on unmount
}, []);

Sharing State Between Screens

Because Zustand stores live outside any component tree, they are perfect for sharing state between screens without prop drilling or React Navigation params. Screen A updates the store, Screen B reads from it — both see the same live state immediately. This is much simpler than passing data through route params for deep navigation hierarchies.

// ScreenA.tsx — writes to store
const setSelectedProduct = useProductStore((s) => s.setSelected);
<Button title='View Details' onPress={() => {
  setSelectedProduct(product);
  navigation.navigate('ProductDetail');
}} />

// ScreenB.tsx — reads from store
const product = useProductStore((s) => s.selected);

Testing Zustand Store Actions

Testing a Zustand store is straightforward because it has no dependencies on React. Import the store, call actions directly on getState(), and assert the updated values. You can also reset the store between tests by calling the reset action or overwriting state with setState to ensure test isolation.

import { useCounterStore } from '../counterStore';

before Each(() => {
  useCounterStore.getState().reset();
});

test('increment increases count by 1', () => {
  useCounterStore.getState().increment();
  expect(useCounterStore.getState().count).toBe(1);
});

test('reset brings count back to 0', () => {
  useCounterStore.setState({ count: 5 });
  useCounterStore.getState().reset();
  expect(useCounterStore.getState().count).toBe(0);
});

Form State with Zustand

Zustand can manage form state that needs to be shared between multiple screens in a multi-step form flow. Store field values and a current step number in the store, and let each screen read and update only its own fields. On final submission, access the complete form data from getState() in the submit handler.

export const useFormStore = create<FormStore>((set) => ({
  step: 1,
  name: '',
  email: '',
  password: '',
  setField: (field, value) => set({ [field]: value }),
  nextStep: () => set((state) => ({ step: state.step + 1 })),
  reset: () => set({ step: 1, name: '', email: '', password: '' }),
}));

Quick Check

Test your understanding of React Native Mobile Development concepts from this lesson.

Lesson Recap

In this lesson you learned: calling the store hook with a selector efficiently subscribes a component to only the state it needs, Zustand actions are plain functions that you pass directly to event handlers, and store.subscribe enables side effects like caching or analytics outside the React lifecycle. Next up we explore persisting Zustand state with AsyncStorage.

よくある質問

「コンポーネントでのStore Stateの読み取りと更新」レッスンは無料ですか？

はい。「コンポーネントでのStore Stateの読み取りと更新」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。

「コンポーネントでのStore Stateの読み取りと更新」で何を学びますか？

useStoreフックを使ってReact Nativeコンポーネントからstoreの値とアクションにアクセスし、ボタン操作やフォーム送信から更新を実行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2/4です。

「コンポーネントでのStore Stateの読み取りと更新」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。

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