react useState useEffect useMemo实际业务场景中的使用

下面的代码实现了上面图片的功能

import React, { useMemo } from "react";
import "./HomeHead.less";
import Img from "../assets/images/timg.jpg";

const HomeHead = function HomeHead(props) {
  { /*父组件传过来的值 */}
    let { today } = props;
  { /*处理时间缓存在状态未改变时是否走暖存，useMemo和vue中计算属性功能类似*/ }

  { /*用useMemo，只有在today变化时，才重新执行time函数,而在更新组件HomeHead时，today未改变，则不执行time函数， today的值走的是缓存和vue的计算属性原理一样*/}
  let time = useMemo(() => {
    //过滤处理时间格式*
    // console.log('@', today.match(/^\d{4}(\d{2})(\d{2})$/))
    let [, month, day] = today.match(/^\d{4}(\d{2})(\d{2})$/);
    let area = [
      "",
      "一",
      "二",
      "三",
      "四",
      "五",
      "六",
      "七",
      "八",
      "九",
      "十",
      "十一",
      "十二",
    ];
    return {
      day,
      month: area[+month] + "月",
    };
  }, [today]);

  return (
    <header className="home-head-box">
      {/*头部左边 */}
      <div className="info">
        <div className="time">
          <span>{time.day}</span>
          <span>{time.month}</span>
        </div>
        <h2 className="title">海鸥移动端博客</h2>
      </div>
      {/*头部右边 */}
      <div className="pictture">
        <img src={Img} alt="头像" />
      </div>
    </header>
  );
};

export default HomeHead;

import React, { useState, useEffect } from "react";
import HomeHead from "../components/HomeHead";
import _ from "../assets/utils"; //  工具函数库，处理时间 formatTime函数
import { Swiper } from "antd-mobile"; // UI组件
import { Link } from "react-router-dom";
import "./Home.less";
import api from "../api";

const Home = () => {
  //创建时间状态 ,_.formatTime(null,'{0}{1}{2}{4}:{5}')当前时间作为初始时间值
  let [today, setToday] = useState(_.formatTime(null, "{0}{1}{2}"));
  // console.log(_.formatTime(null,'{0}{1}{2}{4}:{5}'));

  // 轮播图数据
  let [bannerData, setBannerData] = useState([]);
  // 第一次渲染完毕，请求后台数据,useEffect不能用async修饰，所有里面包一层使用立马执行函数
  useEffect(() => {
    (async () => {
      try {
        // const newData = await api.queryNewsLatest();
        // console.log(newData);
        let { date, stories, top_stories } = await api.queryNewsLatest();
        // 更新时间日期
        setToday(date);
        // 更新bannerData状态
        setBannerData(top_stories);
      } catch (_) {}
    })();
  }, []);

  return (
    <div className="home-box">
      {/*today抓给子组件,头部组件*/}
      <HomeHead today={today} />
      {/*轮播图*/}
      <Swiper autoplay={true} loop={true} className="swiper-box">
        {bannerData.length > 0
          ? bannerData.map((item) => {
              let { image, id, hint, title } = item;
              return (
                <Swiper.Item key={id}>
                  <Link
                    to={{
                      pathname: `/detail/${id}`,
                    }}
                  >
                    <img src={image} alt="" />
                    <div className="desc">
                      <h3 className="title">{hint}邓紫棋</h3>
                      <p className="author">{title}邓紫棋牛逼</p>
                    </div>
                  </Link>
                </Swiper.Item>
              );
            })
          : null}
      </Swiper>
       {/*列表*/}
    </div>
  );
};
export default Home;