[英]How do I use react context API to pass data from parent component to child component when using react-router in the parent component in React.js?
App.js-父組件
import React from 'react';
import { BrowserRouter as Router, Switch, Route } from 'react-router-dom';
import ChildComponent1 from './ChildComponent1';
import ChildComponent2 from './ChildComponent2';
import Context from './Context';
class App extends React.Component {
constructor(props) {
super(props);
this.state = {
messageThatllChange: "changing message",
};
}
render() {
return (
<Router>
<Switch>
<Context.Provider value={this.state.messageThatllChange}>
<Route exact path='/' component={ChildComponent1} />
<Route path='/chat' component={ChildComponent2} />
</Context.Provider>
</Switch>
</Router>
);
}
}
export default App;
ChildComponent1.js-子組件
import React from 'react';
import Context from './Context';
class Join extends React.Component {
static contextType = Context;
constructor(props) {
super(props);
console.log(this.context); // this.context returns undefined.
}
render() {
return (
<div>
{/* Something important here */}
</div>
);
}
}
// Join.contextType = Context; // tried this too
export default Join;
在子組件1的構造函數中,嘗試打印this.context返回undefined
。
如何將上下文從父母傳遞給孩子? 我究竟做錯了什么?
import React from "react";
import ReactDOM from "react-dom";
import "./styles.css";
const Context = React.createContext({ message: "hi" });
class Child extends React.Component {
constructor() {
super();
console.log("Constructor: ", this.context); // undefined here
}
render() {
const message = this.context;
return <p>{message}</p>; // hello here
}
}
Child.contextType = Context;
function App() {
return (
<div className="App">
<Context.Provider value="hello">
<Child />
</Context.Provider>
</div>
);
}
const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);
嘗試在構造函數中打印上下文會返回未定義的內容,但是您應該能夠像這樣在render函數中使用上下文。
您可以在此處運行示例: https : //codesandbox.io/s/crazy-forest-89bd6?fontsize=14
嘗試像下面的其中之一一樣重寫子組件:
動態語境
import React from 'react';
import Context from './Context'; // Context here is the name you defined as Context = React.createContext();
class Join extends React.Component {
render() {
let props = this.props;
let value = this.context;
return (
<div>
{/* Something important here */}
</div>
);
}
}
Join.contextType = Context; // Context here is the name you defined as Context = React.createContext();
export default Join;
Context.Consumer
import React from 'react';
import { Consumer } from './Context'; // the path is where your context file is
class Join extends React.Component {
constructor(props) {
super(props);
}
render() {
return (
<Consumer>
{value => (
{/* Here you can retrieve your messageThatllChange */}
<div>
{/* Something important here */}
</div>
)
</Consumer>
);
}
}
export default Join;
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