reactjs - 如何使用 React Context API 跨多个 Routes 拥有状态？

Question

我试图了解上下文 API 的工作原理。我想保留一个可以从任何类组件更新的全局状态。目前，当我尝试使用提供的函数更新我的 Context 时，它只会在本地更新值。在我的代码中，我尝试将字段“Day”更新为“Hello”，并且只有在呈现 Writer 时才能看到更改。一旦我要求我的浏览器呈现“Reader”，该值又是“Day”。为什么会这样？这是我的代码，我尽可能地简化了它:

index.js:
    import React from "react";
    import ReactDOM from "react-dom";
    import {ThemeContextProvider} from "./ThemeContext";
    
    import App from "./App";
    
    ReactDOM.render(
    <ThemeContextProvider>
       <App />
    </ThemeContextProvider>,
  document.getElementById("root")
);

app.js:
import React from "react";
import Writer from "./Writer.js";
import Reader from "./Reader.js";
import { Context } from "./ThemeContext.js";
import {BrowserRouter as Router, Switch, Route} from 'react-router-dom';

class App extends React.Component {
  static contextType = Context;
  constructor(props) {
    super(props);
  }
  render() {
    return (
      <div className="app">
        <Router>
          <Switch>
            <Route path="/writer" component={Writer}></Route>
            <Route path="/reader" component={Reader}></Route>      
          </Switch>
        </Router>
      </div>
    );
  }
}

export default App;

context.js:
import React, { Component } from "react";
const Context = React.createContext();
const { Provider, Consumer } = Context

// Note: You could also use hooks to provide state and convert this into a functional component.
class ThemeContextProvider extends Component {
  state = {
    theme: "Day"
  };

  setTheme = (newTheme) => {
    this.setState({theme: newTheme})
  };

  render() {
    return <Provider value={{theme: this.state.theme, setTheme: this.setTheme}}>{this.props.children}</Provider>;
  }
}

export { ThemeContextProvider, Consumer as ThemeContextConsumer, Context };

writer.js:
import React from "react";
import {Context} from "./ThemeContext";

class Writer extends React.Component {
  static contextType = Context
  constructor(props) {
    super(props);
    this.write = this.write.bind(this)
  }

  write () {
    this.context.setTheme("hello")
  }

  render() {
    return (
      <div>
        <button onClick={this.write}>press</button>
        <p>{this.context.theme}</p> 
      </div>
    );
  }
}

export default Writer;

reader.js:
import React from "react";
import { Context, ThemeContextConsumer } from "./ThemeContext";

class Reader extends React.Component {
  static contextType = Context;
  constructor(props) {
    super(props);
  }
  render () {
    return(
          <div>
            <p>{this.context.theme}</p>
          </div>
  );}
}

export default Reader;

Answer 1

你如何处理不同页面的操作？如果现在，您可以通过直接在搜索顶部浏览器输入占位符中键入来手动处理它。然后它不会工作，因为页面得到 refresh .仅使用 context api不会使您的数据持久化。您需要合并使用某种 storage让它 坚持 .
无论如何，如果没有页面 refresh，您的代码应该可以工作。发生。要在不同的页面中查看它，您可以和 Link (来自 react-router-dom 包)或基本上是 button将您重定向到不同的页面，如下所示:-

只需将其添加到您的 Writer.js component用于测试目的:-

import React from "react";
import { Link } from 'react-router-dom'
import {Context} from "./ThemeContext";

class Writer extends React.Component {
  static contextType = Context
  constructor(props) {
    super(props);
    this.write = this.write.bind(this)
  }

  write () {
    this.context.setTheme("hello")
  }

  render() {
    return (
      <div>
        <button onClick={this.write}>press</button>
        <p>{this.context.theme}</p> 
        <Link to="/reader">Go to Reader page</Link>
      </div>
    );
  }
}

export default Writer;