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状态管理之Zustand

引言

Zustand 是一个轻量级的状态管理库，以其简单、灵活和高性能的特点在 React 社区中快速崛起。本文将深入探讨 Zustand 的核心概念、使用方法和最佳实践。

1. Zustand 的核心特点

1.1 简单直观的 API

Zustand 采用极简的 API 设计，创建 store 非常简单：

import create from 'zustand'

interface BearStore {
  bears: number
  increase: () => void
  decrease: () => void
}

const useStore = create<BearStore>((set) => ({
  bears: 0,
  increase: () => set((state) => ({ bears: state.bears + 1 })),
  decrease: () => set((state) => ({ bears: state.bears - 1 }))
}))

1.2 无需 Provider

与 Redux 和 Context API 不同，Zustand 不需要 Provider 包裹：

function BearCounter() {
  const bears = useStore((state) => state.bears)
  return <h1>{bears} around here...</h1>
}

function Controls() {
  const increase = useStore((state) => state.increase)
  const decrease = useStore((state) => state.decrease)
  return (
    <div>
      <button onClick={increase}>+</button>
      <button onClick={decrease}>-</button>
    </div>
  )
}

2. 高级特性与用法

2.1 异步操作处理

interface TodoStore {
  todos: Todo[]
  loading: boolean
  fetchTodos: () => Promise<void>
}

const useTodoStore = create<TodoStore>((set) => ({
  todos: [],
  loading: false,
  fetchTodos: async () => {
    set({ loading: true })
    try {
      const response = await fetch('https://api.example.com/todos')
      const todos = await response.json()
      set({ todos, loading: false })
    } catch (error) {
      set({ loading: false })
      console.error(error)
    }
  }
}))

2.2 中间件支持

Zustand 提供了强大的中间件支持：

import { persist, devtools } from 'zustand/middleware'

const useStore = create(
  devtools(
    persist(
      (set) => ({
        bears: 0,
        increase: () => set((state) => ({ bears: state.bears + 1 }))
      }),
      { name: 'bear-storage' }
    )
  )
)

2.3 状态切片（Slices）

组织大型应用状态：

interface AuthSlice {
  user: User | null
  login: (credentials: Credentials) => Promise<void>
  logout: () => void
}

interface TodoSlice {
  todos: Todo[]
  addTodo: (todo: Todo) => void
}

const createAuthSlice = (set) => ({
  user: null,
  login: async (credentials) => {
    const user = await loginApi(credentials)
    set({ user })
  },
  logout: () => set({ user: null })
})

const createTodoSlice = (set) => ({
  todos: [],
  addTodo: (todo) => set((state) => ({ 
    todos: [...state.todos, todo] 
  }))
})

const useStore = create((set) => ({
  ...createAuthSlice(set),
  ...createTodoSlice(set)
}))

3. 性能优化

3.1 选择性订阅

Zustand 支持细粒度的状态订阅：

function TodoCount() {
  // 只在 todos.length 变化时重渲染
  const todoCount = useStore((state) => state.todos.length)
  return <div>Todo Count: {todoCount}</div>
}

3.2 浅比较

使用 shallow 进行浅比较：

import shallow from 'zustand/shallow'

function TodoList() {
  const { todos, addTodo } = useStore(
    (state) => ({ 
      todos: state.todos, 
      addTodo: state.addTodo 
    }),
    shallow
  )
  return (
    // 组件实现
  )
}

4. 实际应用场景

4.1 表单状态管理

interface FormStore {
  formData: {
    name: string
    email: string
  }
  setField: (field: string, value: string) => void
  resetForm: () => void
}

const useFormStore = create<FormStore>((set) => ({
  formData: {
    name: '',
    email: ''
  },
  setField: (field, value) => 
    set((state) => ({
      formData: {
        ...state.formData,
        [field]: value
      }
    })),
  resetForm: () => 
    set({
      formData: {
        name: '',
        email: ''
      }
    })
}))

4.2 认证状态管理

interface AuthStore {
  token: string | null
  user: User | null
  login: (credentials: Credentials) => Promise<void>
  logout: () => void
  updateUser: (user: Partial<User>) => void
}

const useAuthStore = create<AuthStore>()(
  persist(
    (set) => ({
      token: null,
      user: null,
      login: async (credentials) => {
        const { token, user } = await loginApi(credentials)
        set({ token, user })
      },
      logout: () => set({ token: null, user: null }),
      updateUser: (userData) =>
        set((state) => ({
          user: state.user ? { ...state.user, ...userData } : null
        }))
    }),
    {
      name: 'auth-storage',
      getStorage: () => localStorage
    }
  )
)

5. 最佳实践

5.1 Store 组织

// stores/index.ts
import { useAuthStore } from './authStore'
import { useTodoStore } from './todoStore'
import { useUIStore } from './uiStore'

export {
  useAuthStore,
  useTodoStore,
  useUIStore
}

5.2 TypeScript 集成

// types.ts
interface Todo {
  id: string
  title: string
  completed: boolean
}

interface TodoState {
  todos: Todo[]
  loading: boolean
  error: string | null
  addTodo: (title: string) => void
  toggleTodo: (id: string) => void
  removeTodo: (id: string) => void
}

// todoStore.ts
const useTodoStore = create<TodoState>((set) => ({
  todos: [],
  loading: false,
  error: null,
  addTodo: (title) => 
    set((state) => ({
      todos: [
        ...state.todos,
        {
          id: Date.now().toString(),
          title,
          completed: false
        }
      ]
    })),
  toggleTodo: (id) =>
    set((state) => ({
      todos: state.todos.map((todo) =>
        todo.id === id
          ? { ...todo, completed: !todo.completed }
          : todo
      )
    })),
  removeTodo: (id) =>
    set((state) => ({
      todos: state.todos.filter((todo) => todo.id !== id)
    }))
}))

总结

Zustand 的优势在于：

• 简单直观的 API 设计
• 无需 Provider 的使用方式
• 出色的 TypeScript 支持
• 强大的中间件系统
• 优秀的性能表现

使用 Zustand 可以帮助我们：

1. 降低状态管理的复杂度
2. 提高应用的可维护性
3. 优化应用性能
4. 提供更好的开发体验

在选择状态管理方案时，如果你需要一个轻量级但功能强大的解决方案，Zustand 是一个值得考虑的选择。它特别适合中小型应用，但通过良好的状态组织，同样可以胜任大型应用的状态管理需求。