反应上下文 - 'contextType' 未定义 [英] React context - 'contextType' is not defined

问题描述

我正在使用应该支持 react Context 的 react-dom@16.6.1 和 react@16.6.1 并尝试运行一个与 反应上下文:

app.js

import React, { Component } from 'react';从 './components/AppManger' 导入 AppManger；导入'./App.css';export const ThemeContext = React.createContext({a1:'a1'});类 App 扩展组件 {使成为() {返回 (<div className="应用程序"><h1>管理店面服务产品</h1><ThemeContext.Provider value="dark"><应用管理器/></ThemeContext.Provider>

);}}导出默认应用程序；

AppManger.js(没有上下文引用)

import React, { Component } from 'react'从 './SearchBar' 导入 SearchBar；导出默认类 AppManger 扩展组件 {构造函数(道具){超级(道具)；this.onSearchBarChange = this.onSearchBarChange.bind(this);this.state = {搜索值:''，错误加载:假，错误对象:空，}}onSearchBarChange(e) {e.persist();this.setState({ searchValue: e.target.value });}使成为() {返回 (<div><a href="/subsadmin/saml/logout">注销</a><SearchBar onSearchBarChange={this.onSearchBarChange} inAttrView={this.state.onAttrPage}/>

)}}

还有我想在其中使用上下文的 SearchBar.js:

import React, { Component } from 'react';从../App"导入 ThemeContext；导出默认类 SearchBar 扩展组件 {构造函数(道具){超级(道具)；this.state = {showModal: 假,showAttrModal: 假};};componentDidMount(){控制台日志(this.context);//{}}使成为() {const contextType = ThemeContext;控制台日志(上下文类型)；//{}返回 (<div>{contextType}/*'contextType' 未定义 no-undef */<input type="text" style={searchBoxStyle} className="form-control" onChange={this.props.onSearchBarChange} placeholder="搜索..." id="sku" name="sku"/>

)}}

如果我运行应用程序，我会在 SearchBar.js 中得到 Line 44: 'contextType' is not defined no-undef 如果我删除此行，我会在以下情况下得到 {}我记录了 this.context.

解决方案

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

import { ThemeContext } from '../App';导出默认类 SearchBar 扩展组件 {构造函数(道具){超级(道具)；this.state = {showModal: 假,showAttrModal: 假};};静态 contextType = ThemeContext;componentDidMount(){控制台日志(this.context);//{}}使成为() {console.log(this.contextType);//{}返回 (<div>{contextType}/*'contextType' 未定义 no-undef */<input type="text" style={searchBoxStyle} className="form-control" onChange={this.props.onSearchBarChange} placeholder="搜索..." id="sku" name="sku"/>

)}}

I am using react-dom@16.6.1 and react@16.6.1 that should support react Context and trying to run a simple example same as the 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(has no context reference)

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>

        )
    }
}

And the SearchBar.js where I want to use Context:

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>

    )
  }
}

If I run the app I get Line 44: 'contextType' is not defined no-undef in SearchBar.js if I remove this line I get {} when I logging the this.context.

解决方案

You aren't correctly using context, as you need to define it as a static property of the class and import it as a named import since you have exported it as a named import

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>

    )
  }
}

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