如何将 this.state.songs 更新为歌曲列表

Question

我无法更新需要从 songList 获取值的状态歌曲。如何将歌曲更新到 songList ？它与组件生命周期有关吗？运行以下代码时，会抛出“songsList is undefined”错误。 const songList 在 render 中。

    import React, { Component } from 'react';
    import logo from './components/Logo/box8.png';
    import './App.css';
    import SearchBox from './components/SearchBox/SearchBox';
    import SongCards from './components/SongCards/SongCards';
    import 'tachyons';
    import axios from 'axios';

    class App extends Component {
          state = {
            songs : [],
          searchField: '',
          entries: []
          };



      componentDidMount() {
          axios.get(`https://itunes.apple.com/in/rss/topalbums/limit=100/json`)
          .then(response => 
            {this.setState({ entries: response.data.feed.entry });

          });
        }

    onSearchChange=(event)=>{
      this.setState({songs : songsList})
        this.setState({searchField : event.target.value})
        const filteredSongs = this.state.songs.filter(song =>{
          return song.title.toLowerCase().includes(this.state.searchField.toLowerCase())
        });
     }

       render(){

          const songsList = this.state.entries.map(entries => {
          return (
            <SongCards 
              key={entries.id.label} 
              artist={entries["im:artist"].label}
              image={entries["im:image"][2].label}
              link={entries.id.label}
              price={entries["im:price"].label}
              date={entries["im:releaseDate"].label}
              title={entries.title.label}
            />
          );
        });



        return (
          <div className="App">

            <header className="App-header">
              <img src={logo} className="App-logo" alt="logo" />
            </header>
            <SearchBox searchChange= {this.onSearchChange}/>
            {songsList}


      </div>
    );
  }
}

export default App;

Answer 1

感谢您的所有回复。我终于成功了。

import React, { Component } from 'react';
import logo from './components/Logo/box8.png';
import './App.css';
import SearchBox from './components/SearchBox/SearchBox';
import Albums from './components/Albums/Albums';
import Scroll from './components/Scroll/Scroll';
import 'tachyons';
import emoji from 'emoji-dictionary';
import axios from 'axios';

class App extends Component {
      state = {
        show:false,
        songs : [],
      searchField: '',
      };


  componentDidMount() {
      axios.get(`https://itunes.apple.com/in/rss/topalbums/limit=100/json`)
      .then(response => 
        {this.setState({songs:response.data.feed.entry });
         });
    }

itunesPageLoader=()=>{
  this.setState({show:false})
}

onSearchChange=(event)=>{
    this.setState({searchField : event.target.value})

 }

   render(){

    const filteredSongs = this.state.songs.filter(song =>{
      return 
 song.title.label.toLowerCase().includes(this.state.searchField.toLowerCase())
    })

 return (

      <div className="App">


        <header className="App-header">
          <img src={logo} className="App-logo" alt="logo" />
        </header>
        <SearchBox searchChange= {this.onSearchChange}/>
        <Scroll >
        <Albums songs={filteredSongs}/>
        </Scroll>
        <footer className="pv4 ph3 ph5-m ph6-l red">
            <small className="f6 db tc">© 2018 <b className="ttu">Box8 Inc</b>., All 
     Rights Reserved</small>
            <div className="tc mt3">
               {`Made with  ${emoji.getUnicode("purple_heart")} by Renjith`}
            </div>
        </footer>


      </div>
    );
  }
}

export default App;

Answer 2

试试这个。您实际上是使用 setState 将歌曲列表分配给歌曲，但歌曲列表在 onSearchChange 中不存在。要将搜索到的值推送到数组，您需要将 event.target.value 推送到歌曲数组

尝试使用以下更正的代码

  onSearchChange=(event)=>{
       this.setState(prevState => ({songs : [...prevState.songs, event.target.value]}));
        this.setState({searchField : event.target.value})
         const filteredSongs = this.state.songs.filter(song =>{
         return song.title.toLowerCase().includes(this.state.searchField.toLowerCase())
        });
     }

Answer 3

您提到this.state.entries 是Object。
如果这是真的，那么你不能对它执行.map，因为.map 是Array 方法。

但是，您可以使用Object.entries 来获取[key,value] 对this.state.entries 的数组。

Object.entries(this.state.entries).map(([key,value]) => ...)

简单运行示例：

const object1 = { foo: 'this is foo', baz: "this is baz" };
Object.entries(object1).map(([key,value]) => console.log(`key: ${key}, value: ${value}`));

Answer 4

所以我会这样做：

const IN_PROGRESS = 'IN_PROGRESS';
const SUCCESS = 'SUCCESS';

class App extends Component {
  state = {
    songs : null,
    entries: null,
    status: null
  };

  componentDidMount() {
     this.setState({status: IN_PROGRESS});

     axios.get(`https://itunes.apple.com/in/rss/topalbums/limit=100/json`)
      .then({data} => {
        const songs = data.feed.entry;

        this.setState({entries: songs});
        this.setState({songs});
        this.setState({status: SUCCESS});
      });
    }

  onSearchChange = ({target}) => {
    const {value} = target;

    const songs = this.state.entires.filter(song => 
      song.title.toLowerCase().includes(value.toLowerCase())
    });

    this.setState({songs});
  }

  render() {
    const {status, songs} = this.state;

    return (
      <div className="App">
        <header className="App-header">
          <img src={logo} className="App-logo" alt="logo" />
        </header>

        <SearchBox searchChange={this.onSearchChange}/>

        {
           status === IN_PROGRESS && 
            (/* you can insert here some kind of loader which indicates that data is loading*/)
        }

        {
           status === SUCCESS && songs.map(entry => {
             const {
               id, ['im:artist']: artist, ['im:image']: image,
               ['im:price']: price, ['im:releaseDate']: date, title
             } = entry;

             return (
               <SongCard
                 key={id.label} 
                 artist={artist.label}
                 image={image[2].label}
                 link={id.label}
                 price={price.label}
                 date={date.label}
                 title={entry.title.label}
               />
             )
           }
        }

        {
           //Here you can display error message if status === FAILURE
        }
      </div>
    );
  }
}

1. 当组件确实挂载时，我将状态设置为 IN_PROGRESS（如果您希望显示某种加载程序），并且正在获取数据 - axios.get 是异步的，因此请记住，当获取数据时，渲染方法已经被触发。加载数据后，在状态下我保存两个变量，entries 保存未过滤的歌曲列表，songs 保存过滤后的歌曲。
2. 当search 被触发时，我会按搜索到的短语过滤entires，并将此过滤后的数组设置为状态。
3. 组件通过过滤songs 渲染songCards 映射