useReducer和useContext前面有单独介绍过，上手不难，现在我们把这两个api结合起来使用，该怎么用？还是结合之前的简易增删改查的demo，熟悉vue的应该可以看出，useReducer类似于vuex，useContext类似于vue中的inject和provided,来分析下思路。

实现效果

代码实现

• 文件拆解
  
• 组件入口文件 -> index.js

import { TasksContext, TasksDispatchContext } from "./context";
import { useReducer } from "react";
import { initialTasks } from "./taskLists";
import { taskReucers } from "./tasksReducer";
import AddTask from "./AddTask";
import TaskList from "./TaskList";
function State() {const [tasks, dispatch] = useReducer(taskReucers, initialTasks);return (<TasksContext.Provider value={tasks}><TasksDispatchContext.Provider value={dispatch}><AddTask /><TaskList /></TasksDispatchContext.Provider></TasksContext.Provider>);
}export default State;

• AddTask.js

import { useState, useContext } from "react";
import { TasksDispatchContext } from "./context";
let nextId = 3;function AddTask() {let [msg, setMsg] = useState("");const dispatch = useContext(TasksDispatchContext);const handleSubmit = () => {if (!msg) return;setMsg("");dispatch({type: "added",task: {id: nextId++,text: msg,done: false,},});};const handleChange = (e) => {setMsg(e.target.value);};return (<><input type="text" value={msg} onChange={handleChange} /><button onClick={handleSubmit}>添加</button></>);
}export default AddTask;

• context.js文件

import { createContext } from "react";export const TasksContext = createContext(null);
export const TasksDispatchContext = createContext(null);

• taskReucers.js

export function taskReucers(state = [], action) {switch (action.type) {case "added":return [...state, action.task];case "changed":return state.map((task) => {if (task.id === action.task.id) {return action.task;} else return task;});case "deleted":return state.filter((task) => task.id !== action.task.id);default:throw new Error("Action type not found");}
}

• taskListsData.js

export const initialTasks = [{ id: 0, text: "Philosopher’s Path", done: true },{ id: 1, text: "Visit the temple", done: false },{ id: 2, text: "Drink matcha", done: false },
];

• TaskList.js

import { useState, useContext } from "react";
import Task from "./Task";
import { TasksContext } from "./context";function TaskList() {const [isEdit, setIsEdit] = useState(false);const tasks = useContext(TasksContext);const handleChangeValue = (value) => {};return (<ul>{tasks.map((task) => {return <Task key={task.id} task={task} />;})}</ul>);
}export default TaskList;

• Task.js

import { useState, useContext } from "react";
import { TasksDispatchContext } from "./context";
function Task({ task }) {const [isEdit, setIsEdit] = useState(false);const dispatch = useContext(TasksDispatchContext);let todoContent = "";function handleChangeText(e) {dispatch({ type: "changed", task: { id: task.id, text: e.target.value } });}function handleDeleteTask(id) {dispatch({ type: "deleted", task: { id } });}if (isEdit) {todoContent = (<span><input type="text" value={task.text} onChange={handleChangeText} /><button onClick={() => setIsEdit(false)}>完成</button></span>);} else {todoContent = (<span><span>{task.text}</span><button onClick={() => setIsEdit(true)}>编辑</button></span>);}return (<li>{todoContent}<button onClick={() => handleDeleteTask(task.id)}>删除</button></li>);
}export default Task;

这样拆解后，明显的业务更加清晰，容易维护了，给后续接手的人一目了然的理解思路。
没有了组件层级之间的繁琐的层层传递数据和方法，代码结构也很清晰了。

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进一步的优化业务代码

• context.js的封装

import { createContext, useReducer } from "react";
import { initialTasks } from "./taskListsData";
import { taskReucers } from "./tasksReducer";export const TasksContext = createContext(null);
export const TasksDispatchContext = createContext(null);export default function TasksProvider({ children }) {const [tasks, dispatch] = useReducer(taskReucers, initialTasks);return (<TasksContext.Provider value={tasks}><TasksDispatchContext.Provider value={dispatch}>{children}</TasksDispatchContext.Provider></TasksContext.Provider>);
}

• 入口文件index.js的优化

import AddTask from "./AddTask";
import TaskList from "./TaskList";
import TasksProvider from "./context";
function State() {return (<TasksProvider><AddTask /><TaskList /></TasksProvider>);
}export default State;

这样实现了同样的效果，代码更加精简。