javascript - react : Passing an object to state

Question

我正在尝试使用 Spotify Web API 制作 Spotify Web Player 的副本。现在，我正在尝试使用 onClick 事件处理程序设置 activePlaylist。但是，当我将我的播放列表对象传递给事件处理程序方法时，该对象是未定义的。我已经尝试解决这个问题很长时间了。你有什么建议吗？

注意:它会很好地将名称映射到页面，但是当我将它传递给事件处理程序方法时，该对象变为未定义。

这是我的代码:

import React, { Component } from 'react';
import '../css/playlists.css';

class Playlists extends Component {
  constructor(props) {
    super(props);

    this.state = {
      activePlaylist: null
    };
  }

  setActivePlaylist(playlist) {
    console.log('From setActivePlaylist');
    console.log(playlist.name); //this logs as undefined
  }

  render() {
    const {playlists} = this.props;

    return(
      <div className='playlists'>
        <h4 id='playlist-label'>Playlists</h4>
        {this.props.playlists
          ?
          (this.props.playlists.items.map((playlist, index)=>
            <a href="#" onClick={(playlist) => this.setActivePlaylist(playlist)}>
              <h4
              key={index}
              >
                {playlist.name}
              </h4>
            </a>
          ))
          :
          (<h4>Loading playlists...</h4>)
        }
      </div>
    );
  }
}

export default Playlists;

Answer 1

您需要绑定(bind)上下文以便您可以访问该类。下面是它可能看起来像下面的片段。为了便于阅读，我分解了逻辑。

此外，您试图覆盖与传入变量同名的事件参数 - 因此“播放列表”是事件对象，而不是您期望的对象”

onClick={/* this be no good-->*/ (**playlist**) => this.setActivePlaylist(playlist)}

你可以在这里看到一个演示: https://stackblitz.com/edit/react-passing-an-object-to-state?file=Playlists.js

import React, { Component } from 'react';

class Playlists extends Component {

  constructor(props) {
    super(props);

    this.state = {
      activePlaylist: null
    };

    // Need to bind the scoped context so we have access to "Playlists" component.
    this.renderLink = this.renderLink.bind(this);
  }

  setActivePlaylist(playlist) {
    console.log('From setActivePlaylist');
    console.log(playlist.name);
  }

  render() {
    const {items} = this.props.playlists

    return(
      <div className='playlists'>
        <h4 id='playlist-label'>Playlists</h4>
        {items
          ? items.map(this.renderLink)
          : <h4>Loading playlists...</h4>
        }
      </div>
    );
  }

  renderLink(playlist, index) {
    return (
      <a onClick={() => this.setActivePlaylist(playlist)}>
        <h4 key={index}>
            {playlist.name}
          </h4>
        </a>
    );
  }
}

export default Playlists;

还要确保在构造函数中绑定(bind) setActivePlaylist 或使其成为箭头函数