迁移状态逻辑至 Reducer 中

编写reducer

在组件中使用reducer

import { useReducer } from 'react';
import AddTask from './AddTask.js';
import TaskList from './TaskList.js';

export default function TaskApp() {
  const [tasks, dispatch] = useReducer(tasksReducer, initialTasks);

  function handleAddTask(text) {
    dispatch({
      type: 'added',
      id: nextId++,
      text: text,
    });
  }

  function handleChangeTask(task) {
    dispatch({
      type: 'changed',
      task: task,
    });
  }

  function handleDeleteTask(taskId) {
    dispatch({
      type: 'deleted',
      id: taskId,
    });
  }

  return (
    <>
      <h1>布拉格的行程安排</h1>
      <AddTask onAddTask={handleAddTask} />
      <TaskList
        tasks={tasks}
        onChangeTask={handleChangeTask}
        onDeleteTask={handleDeleteTask}
      />
    </>
  );
}

function tasksReducer(tasks, action) {
  switch (action.type) {
    case 'added': {
      return [
        ...tasks,
        {
          id: action.id,
          text: action.text,
          done: false,
        },
      ];
    }
    case 'changed': {
      return tasks.map((t) => {
        if (t.id === action.task.id) {
          return action.task;
        } else {
          return t;
        }
      });
    }
    case 'deleted': {
      return tasks.filter((t) => t.id !== action.id);
    }
    default: {
      throw Error('未知 action: ' + action.type);
    }
  }
}
let nextId = 3;
const initialTasks = [
  {id: 0, text: '参观卡夫卡博物馆', done: true},
  {id: 1, text: '看木偶戏', done: false},
  {id: 2, text: '打卡列侬墙', done: false}
];

reducer文件单独抽出来