Javascript Can';无法访问React上下文
我最近尝试在我的React应用程序中实现上下文,但我无法在chlid组件上访问我的上下文 原则如下: jsindex.js提供了一个上下文,该上下文声明了一个与用户的登录状态相对应的值(false) 如果App.js在localstorage中检测到JWT存储,则上下文将更新为true,并呈现某个组件 代码如下: AppContext.jsJavascript Can';无法访问React上下文,javascript,reactjs,state,Javascript,Reactjs,State,我最近尝试在我的React应用程序中实现上下文,但我无法在chlid组件上访问我的上下文 原则如下: jsindex.js提供了一个上下文,该上下文声明了一个与用户的登录状态相对应的值(false) 如果App.js在localstorage中检测到JWT存储,则上下文将更新为true,并呈现某个组件 代码如下: AppContext.js import React from 'react' export const AppContext = React.createContext({ i
import React from 'react'
export const AppContext = React.createContext({
isUserLogged: false
})
import React from 'react'
import ReactDOM from 'react-dom'
import './assets/sakura/app.css'
import App from './components/App'
import * as serviceWorker from './serviceWorker'
import { AppContext } from './context/AppContext'
ReactDOM.render((
<AppContext.Provider>
<App />
</AppContext.Provider>
), document.getElementById('root'));
import React from 'react'
import Auth from './auth/Auth'
import Main from './main/Main'
import { AppContext } from '../context/AppContext'
class App extends React.Component {
constructor(props) {
super(props)
this.state = {
userToken: localStorage.getItem('spotlight-token'),
isUserLogged: false
}
}
UNSAFE_componentWillMount() {
if (this.state.userToken) this.setState({isUserLogged: true})
}
static contextType = AppContext
render() {
console.log(this.context)
const isUserLogged = this.state.isUserLogged
return isUserLogged ? <Main /> : <Auth />
}
}
export default App
index.js
import React from 'react'
export const AppContext = React.createContext({
isUserLogged: false
})
import React from 'react'
import ReactDOM from 'react-dom'
import './assets/sakura/app.css'
import App from './components/App'
import * as serviceWorker from './serviceWorker'
import { AppContext } from './context/AppContext'
ReactDOM.render((
<AppContext.Provider>
<App />
</AppContext.Provider>
), document.getElementById('root'));
import React from 'react'
import Auth from './auth/Auth'
import Main from './main/Main'
import { AppContext } from '../context/AppContext'
class App extends React.Component {
constructor(props) {
super(props)
this.state = {
userToken: localStorage.getItem('spotlight-token'),
isUserLogged: false
}
}
UNSAFE_componentWillMount() {
if (this.state.userToken) this.setState({isUserLogged: true})
}
static contextType = AppContext
render() {
console.log(this.context)
const isUserLogged = this.state.isUserLogged
return isUserLogged ? <Main /> : <Auth />
}
}
export default App
从“React”导入React
从“react dom”导入react dom
导入“./assets/sakura/app.css”
从“./components/App”导入应用程序
将*作为serviceWorker从“./serviceWorker”导入
从“./context/AppContext”导入{AppContext}
ReactDOM.render((
),document.getElementById('root');
App.js
import React from 'react'
export const AppContext = React.createContext({
isUserLogged: false
})
import React from 'react'
import ReactDOM from 'react-dom'
import './assets/sakura/app.css'
import App from './components/App'
import * as serviceWorker from './serviceWorker'
import { AppContext } from './context/AppContext'
ReactDOM.render((
<AppContext.Provider>
<App />
</AppContext.Provider>
), document.getElementById('root'));
import React from 'react'
import Auth from './auth/Auth'
import Main from './main/Main'
import { AppContext } from '../context/AppContext'
class App extends React.Component {
constructor(props) {
super(props)
this.state = {
userToken: localStorage.getItem('spotlight-token'),
isUserLogged: false
}
}
UNSAFE_componentWillMount() {
if (this.state.userToken) this.setState({isUserLogged: true})
}
static contextType = AppContext
render() {
console.log(this.context)
const isUserLogged = this.state.isUserLogged
return isUserLogged ? <Main /> : <Auth />
}
}
export default App
从“React”导入React
从“./Auth/Auth”导入身份验证
从“/Main/Main”导入Main
从“../context/AppContext”导入{AppContext}
类应用程序扩展了React.Component{
建造师(道具){
超级(道具)
此.state={
userToken:localStorage.getItem('spotlight-token'),
isUserLogged:false
}
}
不安全的_组件willmount(){
if(this.state.userToken)this.setState({isUserLogged:true})
}
静态contextType=AppContext
render(){
console.log(this.context)
const isUserLogged=this.state.isUserLogged
是否返回isUserLogged?:
}
}
导出默认应用程序
但问题是,控制台返回未定义的,我不明白为什么
感谢您的帮助,我知道这听起来有点愚蠢,但我是一个纯粹的宽度上下文初学者,非常想理解它。阅读标题下的示例,从嵌套组件更新上下文:
app.js
import {ThemeContext, themes} from './theme-context';
import ThemeTogglerButton from './theme-toggler-button';
class App extends React.Component {
constructor(props) {
super(props);
this.toggleTheme = () => {
this.setState(state => ({
theme:
state.theme === themes.dark
? themes.light
: themes.dark,
}));
};
// State also contains the updater function so it will
// be passed down into the context provider
this.state = {
theme: themes.light,
toggleTheme: this.toggleTheme,
};
}
render() {
// The entire state is passed to the provider
return (
<ThemeContext.Provider value={this.state}>
<Content />
</ThemeContext.Provider>
);
}
}
function Content() {
return (
<div>
<ThemeTogglerButton />
</div>
);
}
ReactDOM.render(<App />, document.root);
从“/theme context”导入{ThemeSecontext,themes};
从“./主题切换按钮”导入主题切换按钮;
类应用程序扩展了React.Component{
建造师(道具){
超级(道具);
this.toggleTheme=()=>{
this.setState(state=>({
主题:
state.theme==themes.dark
?主题、光
:themes.dark,
}));
};
//State还包含updater函数,因此
//被传递到上下文提供程序中
此.state={
主题:themes.light,
toggleTheme:this.toggleTheme,
};
}
render(){
//整个状态将传递给提供程序
返回(
);
}
}
函数内容(){
返回(
);
}
render(,document.root);
theme-toggler-button.js
import {ThemeContext} from './theme-context';
function ThemeTogglerButton() {
// The Theme Toggler Button receives not only the theme
// but also a toggleTheme function from the context
return (
<ThemeContext.Consumer>
{({theme, toggleTheme}) => (
<button
onClick={toggleTheme}
style={{backgroundColor: theme.background}}>
Toggle Theme
</button>
)}
</ThemeContext.Consumer>
);
}
export default ThemeTogglerButton;
从“/主题上下文”导入{ThemeContext};
函数ThemeTogglerButton(){
//主题切换按钮不仅接收主题
//而且还有一个来自上下文的toggleTheme函数
返回(
{({theme,toggleTheme})=>(
切换主题
)}
);
}
导出默认的切换按钮;
您的提供程序没有值好的,但该值不是在AppContext.js?@RenaudMonell中传递的值,这是默认值,以防您忘记呈现提供程序。渲染提供程序时,应通过其值属性传入所需的值。目前你没有这个道具,所以你指定了未定义。非常感谢!这个概念有点模糊,现在我需要找到如何改变它的价值,我会很好@雷纳德·莫内尔把它当作道具传进来。