Question

所以我学会了反应，但是在练习时需要一些帮助。这可能很长，但是您的帮助将不胜感激。以下代码均无效，因此我只想找出我做错了什么。我设置了以下上下文，它是对象数组

import React, {createContext, useState} from 'react';

export const Songlist = createContext()

const TheSongs = (props) => {
    const [songs, setSongs] = useState([
        {title: "deliverance", artist: "opeth", id: 0},
        {title: "civil war", artist: "guns n roses", id: 1},
        {title: "heaven and hell", artist: "black sabbath", id: 2},
        {title: "anesthetize", artist: "porcupine tree", id: 3}
    ])
    const songList = () =>{
        setSongs(songs.forEach(song =>{
            return(
                <div className="container" key={song.id}>
                    <h4>{song.title}</h4>
                    <h3>{song.artist}</h3>
                </div>
            )
        }))
    }
    return ( 
        <Songlist.Provider value={songs, songList}>
            {props.children}
        </Songlist.Provider>
     );
}

export default TheSongs;

然后我试图在这样的组件中调用它

import React, {useContext} from 'react';
import {Songlist} from '../contexts/TheWorld'

const SongListUI = () => {

    const {songList} = useContext(Songlist)


    return ( 
        <div className="hi">
            {songList}
        </div>
     );
}

export default SongListUI;

没有发生错误，但是什么也没有呈现，并且名为“ hi”的div也不包含任何内容。

然后我只是将数组保留在上下文中，并再次使用Context在组件中调用它，但是这次我尝试了一些不同的事情，那就是

import React, {useContext} from 'react';
import {Songlist} from '../contexts/TheWorld'

const SongListUI = () => {

    const {songs} = useContext(Songlist)

    const songList = () =>{
      songs.forEach(song =>{
        return(
            <div className="container" key={song.id}>
                <h4>{song.title}</h4>
                <h3>{song.artist}</h3>
            </div>
        )
    })
}

    return ( 
        <div className="hi">
            {songList}
        </div>
     );
}

export default SongListUI;

我收到一个错误，指出不允许将函数作为react子元素，并且div中仍然没有任何内容，因此我再次尝试了不同的方法，我在forEach内应用了jsx循环，函数的名称，但仍然无法正常工作，并且在“ hi” div中未呈现任何内容。所以我取消了整个上下文，并在组件本身内部使用了useState钩子

import React, {useState} from 'react';

const SongListUI = () => {

    const [songs, setSongs] = useState([
        {title: "deliverance", artist: "opeth", id: 0},
        {title: "civil war", artist: "guns n roses", id: 1},
        {title: "heaven and hell", artist: "black sabbath", id: 2},
        {title: "anesthetize", artist: "porcupine tree", id: 3}
    ])

    const songlist = () =>{
        setSongs(songs.forEach(song =>{
            return(
                <div className="container" key={song.id}>
                    <h4>{song.title}</h4>
                    <h3>{song.artist}</h3>
                </div>
            )
        }))
    }


    return ( 
        <div className="hi">
            {songlist}
        </div>
     );
}

export default SongListUI;

由于再次发生子反应错误而无法正常工作，所以

import React, {useState} from 'react';

const SongListUI = () => {

    const [songs, setSongs] = useState([
        {title: "deliverance", artist: "opeth", id: 0},
        {title: "civil war", artist: "guns n roses", id: 1},
        {title: "heaven and hell", artist: "black sabbath", id: 2},
        {title: "anesthetize", artist: "porcupine tree", id: 3}
    ])


    return ( 
        <div className="hi">
            {
                songs.forEach(song =>{
                    return(
                        <div key={song.id}>
                            <h4>{song.title}</h4>
                            <h3>{song.artist}</h3>
                        </div>
                    )
                })
            }
        </div>
     );
}

export default SongListUI;

仍然没有任何效果，所以我只想知道我在做错什么...

Answer 1

forEach的返回值为undefined。您能否在歌曲上使用.map来代替上一个示例？

即

songs.map((song) => <div key={song.id}><h4>{song.title}</h4><h3>{song.artist}</h3></div>)

为什么在React js中未呈现组件？

1 个答案: