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。

---

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。