React 上下文 - 'contextType' 未定义

Question

我正在使用 react-dom@16.6.1 和 react@16.6.1 应该支持 react Context 并尝试运行一个与 react-context:

app.js

import React, { Component } from 'react';
import AppManger from './components/AppManger';
import './App.css';
export const ThemeContext = React.createContext({a1:'a1'});

class App extends Component {

  render() {

    return (

      <div className="App">
        <h1>Manage Storefront Services Products</h1>
        <ThemeContext.Provider value="dark">
          <AppManger />
        </ThemeContext.Provider>

      </div>

    );
  }
}

export default App;

AppManger.js（没有上下文引用）

import React, { Component } from 'react'
import SearchBar from './SearchBar';
export default class AppManger extends Component {


    constructor(props) {
        super(props);
        this.onSearchBarChange = this.onSearchBarChange.bind(this);
        this.state = {
            searchValue: '',
            errorLoading: false,
            errorObj: null,
        }
    }

    onSearchBarChange(e) {
        e.persist();
        this.setState({ searchValue: e.target.value });
    }

    render() {
        return (

            <div>
                <a href="/subsadmin/saml/logout">Log out</a>
                <SearchBar onSearchBarChange={this.onSearchBarChange} inAttrView={this.state.onAttrPage} />
            </div>

        )
    }
}

还有SearchBar.js我想使用上下文的地方：

import React, { Component } from 'react';
import ThemeContext from '../App';


export default class SearchBar extends Component {
  constructor(props) {
    super(props);
    this.state = {
      showModal: false,
      showAttrModal: false
    };

  };


  componentDidMount(){
    console.log(this.context); //{}
  }

  render() {
    const contextType = ThemeContext;
    console.log(contextType); //{}
    return (

      <div>
        {contextType} /*'contextType' is not defined  no-undef */
        <input type="text" style={searchBoxStyle} className="form-control" onChange={this.props.onSearchBarChange} placeholder="Search for..." id="sku" name="sku" />

      </div>

    )
  }
}

如果我运行该应用程序，我会在 SearchBar.js 中得到 Line 44: 'contextType' is not defined no-undef 如果我删除此行，我会在记录 this.context 时得到 {}。

Answer 1

这里的问题：

componentDidMount() {
    console.log(this.context);
}

这里找不到 this.context 变量。

static contextType = 

To

const contextType =

Answer 2

您导入了 App 而不是 ThemeContext。

使用import { ThemeContext } from '../App.js;

Answer 3

您没有正确使用上下文，因为您需要将其定义为 class 的静态属性并将其导入为命名导入，因为您已将其导出为命名导入

import { ThemeContext } from '../App';

export default class SearchBar extends Component {
  constructor(props) {
    super(props);
    this.state = {
      showModal: false,
      showAttrModal: false
    };

  };

  static contextType = ThemeContext;
  componentDidMount(){
    console.log(this.context); //{}
  }

  render() {

    console.log(this.contextType); //{}
    return (

      <div>
        {contextType} /*'contextType' is not defined  no-undef */
        <input type="text" style={searchBoxStyle} className="form-control" onChange={this.props.onSearchBarChange} placeholder="Search for..." id="sku" name="sku" />

      </div>

    )
  }
}

React 上下文 - 'contextType' 未定义

React context - 'contextType' is not defined

javascript

reactjs

react-context