[React] Use the useReducer Hook and Dispatch Actions to Update State (useReducer, useMemo, useEffect...

最新推荐文章于 2025-02-25 20:25:08 发布

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最新推荐文章于 2025-02-25 20:25:08 发布

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原文链接：http://www.cnblogs.com/Answer1215/p/10426941.html

本文探讨了在React中使用useReducer钩子替代useState的方法，通过集中管理分散在Web应用中的逻辑，实现更高效的状态更新。文章详细介绍了useReducer的用法，包括初始化状态、处理副作用及使用useEffect进行本地存储的更新。

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As an alternate to useState, you could also use the useReducer hook that provides state and a dispatch method for triggering actions. In this lesson, we’ll centralize logic that is spread across a web application and centralize it using the useReducer hook.

NOTE: Since hooks are still a proposal and only pre-released, it’s not currently recommended to use them in production.

useReducer:

  const [todos, dispatch] = useReducer((state, action) => {
    switch (action.type) {
      case "ADD_TODO":
        todoId.current += 1;
        return [
          ...state,
          { id: todoId.current, text: action.text, completed: false }
        ];
      case "DELETE_TODO":
        return state.filter(todo => todo.id !== action.id);
      case "TOGGLE_TODO":
        return state.map(todo =>
          todo.id === action.id ? { ...todo, completed: !todo.completed } : todo
        );
      default:
        return state;
    }
  },initialValue);

useReducer can accept second param as a function, so we can replace 'initialValue' with a function return a 'initialValue', which means we can using cache for the function if the param doesn't change, we always return the cache. To do that we can use

useMemo:

  const [todos, dispatch] = useReducer((state, action) => {
    switch (action.type) {
      case "ADD_TODO":
        todoId.current += 1;
        return [
          ...state,
          { id: todoId.current, text: action.text, completed: false }
        ];
      case "DELETE_TODO":
        return state.filter(todo => todo.id !== action.id);
      case "TOGGLE_TODO":
        return state.map(todo =>
          todo.id === action.id ? { ...todo, completed: !todo.completed } : todo
        );
      default:
        return state;
    }
  }, useMemo(initialValue, []));

The second parameter of 'useMemo' indicates when the memorized version should change. In our case, we want it to always be the same, so passing an empty array conveys that message.

To handle side effect of action, in our case, is update localstorage, we can use useEffect:

useEffect(
  () => {
    window.localStorage.setItem("todos", JSON.stringify(todos));
  },
  [todos]
);

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转载于:https://www.cnblogs.com/Answer1215/p/10426941.html