React Native Academy · レッスン

SlicesパターンとDevtoolsの統合

Slicesパターンを使って大規模なstoreを論理的なsliceに整理し、Zustand DevToolsミドルウェアを追加して開発時のタイムトラベルデバッグを行います

「SlicesパターンとDevtoolsの統合」はCoddyKit上の無料React Native Academyレッスンです。これはレッスン4/4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。

Why Organize Stores with Slices?

As a Zustand store grows, keeping all state and actions in a single object becomes hard to maintain. The slices pattern splits the store into multiple focused sections, each defined as a separate function. All slices are combined into one store, so components still access everything through a single hook. This mirrors the Redux Toolkit slice concept but in Zustand's minimal style.

Defining a Slice Function

A Zustand slice is a function that accepts set, get, and optionally the whole store initializer, and returns an object containing state and actions for that domain. Define each slice in its own file and import them into the combined store. The slice function signature mirrors the main store creator exactly.

// slices/counterSlice.ts
import type { StateCreator } from 'zustand';
import type { AppStore } from '../useAppStore';

export interface CounterSlice {
  count: number;
  increment: () => void;
  decrement: () => void;
  reset: () => void;
}

export const createCounterSlice: StateCreator<AppStore, [], [], CounterSlice> =
  (set) => ({
    count: 0,
    increment: () => set((state) => ({ count: state.count + 1 })),
    decrement: () => set((state) => ({ count: state.count - 1 })),
    reset: () => set({ count: 0 }),
  });

Combining Slices into One Store

Import all your slice creator functions and merge them inside a single create call using the spread operator. The combined store type is the intersection of all slice interfaces. Components can then access any slice's state and actions through the same useAppStore hook.

// useAppStore.ts
import { create } from 'zustand';
import { createCounterSlice, CounterSlice } from './slices/counterSlice';
import { createUserSlice, UserSlice } from './slices/userSlice';

export type AppStore = CounterSlice & UserSlice;

export const useAppStore = create<AppStore>((set, get, api) => ({
  ...createCounterSlice(set, get, api),
  ...createUserSlice(set, get, api),
}));

Cross-Slice Communication

Slices can call each other's actions or read each other's state using the get function. This is how one slice can react to another slice's changes without tight coupling. For example, a cart slice can read the user slice's auth token and include it in an API request when checking out.

export const createCartSlice: StateCreator<AppStore, [], [], CartSlice> =
  (set, get) => ({
    items: [],
    checkout: async () => {
      const token = get().user.token; // read from userSlice
      await api.checkout(get().items, token);
      set({ items: [] });
    },
  });

What Is the Zustand DevTools Middleware?

The devtools middleware connects your Zustand store to the Redux DevTools browser extension. Once connected, you can inspect every state snapshot, view the action name that triggered each change, and time-travel back to any previous state. It is invaluable for debugging complex state sequences during development.

Adding DevTools Middleware

Wrap your store creator with the devtools middleware imported from zustand/middleware. Pass an optional configuration object with a name property to label the store in the DevTools panel. Only enable DevTools in development to avoid performance overhead in production builds.

import { create } from 'zustand';
import { devtools } from 'zustand/middleware';

export const useCounterStore = create(
  devtools(
    (set) => ({
      count: 0,
      increment: () => set((state) => ({ count: state.count + 1 })),
      reset: () => set({ count: 0 }),
    }),
    { name: 'CounterStore' }
  )
);

Labeling Actions in DevTools

By default, DevTools labels every state change with anonymous. Pass a descriptive string as the third argument to set to give each action a meaningful name in the DevTools timeline. This makes it much easier to trace which user interaction triggered each state change.

increment: () =>
  set(
    (state) => ({ count: state.count + 1 }),
    false,              // false = merge (not replace)
    'counter/increment' // action label in DevTools
  ),
reset: () =>
  set({ count: 0 }, false, 'counter/reset'),

Combining DevTools with persist

When using both persist and devtools, wrap the store in both middlewares. The order matters: devtools should be the outermost wrapper so it can observe all state changes, including those from rehydration. Nest persist inside devtools to see rehydration actions in the DevTools timeline.

import { create } from 'zustand';
import { persist, devtools, createJSONStorage } from 'zustand/middleware';
import AsyncStorage from '@react-native-async-storage/async-storage';

export const useSettingsStore = create(
  devtools(
    persist(
      (set) => ({ theme: 'light', setTheme: (t) => set({ theme: t }) }),
      { name: 'settings', storage: createJSONStorage(() => AsyncStorage) }
    ),
    { name: 'SettingsStore' }
  )
);

Slices with persist and DevTools

In large apps, combine all three patterns: slices for organization, persist for storage, and devtools for debugging. Wrap the merged slice object with persist and devtools. Define the combined type as the intersection of all slice interfaces so TypeScript correctly types the full store.

export const useAppStore = create<AppStore>()(
  devtools(
    persist(
      (set, get, api) => ({
        ...createCounterSlice(set, get, api),
        ...createUserSlice(set, get, api),
      }),
      { name: 'app-store', storage: createJSONStorage(() => AsyncStorage) }
    ),
    { name: 'AppStore' }
  )
);

Naming Conventions for Slices

Use consistent naming to make large stores easy to navigate. Name slice files after the domain (e.g., authSlice.ts, cartSlice.ts), prefix action names with the domain in DevTools labels (e.g., auth/login, cart/addItem), and keep each slice under 100 lines. Split further if a slice starts handling unrelated concerns.

When Not to Use Slices

The slices pattern adds complexity. If your store has fewer than five state fields and two or three actions, keep it as a single create call — the overhead of splitting is not worth it. Reserve slices for stores that have grown to the point where a single file is difficult to understand or when multiple developers work on different features that share the same store.

Quick Check

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

Lesson Recap

In this lesson you learned: the slices pattern splits a large Zustand store into focused domain functions that are merged in one create call, the devtools middleware connects the store to Redux DevTools for state inspection and time-travel, and labeling set calls with action name strings makes the DevTools timeline meaningful. Next up we explore reading and writing with AsyncStorage directly.

よくある質問

「SlicesパターンとDevtoolsの統合」レッスンは無料ですか？

はい。「SlicesパターンとDevtoolsの統合」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。

「SlicesパターンとDevtoolsの統合」で何を学びますか？

Slicesパターンを使って大規模なstoreを論理的なsliceに整理し、Zustand DevToolsミドルウェアを追加して開発時のタイムトラベルデバッグを行い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4/4です。

「SlicesパターンとDevtoolsの統合」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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