React JS - Route - 元素类型无效

Question

我是React JS的新手，我正在尝试实现类似于Angular示例应用程序的东西。

我有一个客户表，希望在表格底部看到所选客户。

我用react-router-dom尝试了以下方法：

// index.js 
import React from 'react';
import ReactDOM from 'react-dom';
import { BrowserRouter } from 'react-router-dom';
import './index.css';
import App from './App';
import registerServiceWorker from './registerServiceWorker';
import 'bootstrap/dist/css/bootstrap.css';

ReactDOM.render((<BrowserRouter><App /></BrowserRouter>), document.getElementById('root'));
registerServiceWorker();


// App.js
import React, { Component } from 'react';
import { Route } from 'react-router-dom/Route';

import Customers from './components/customers';
import Customer from './components/customer';

export default class App extends Component {
    state = {
    };

    render() {
        return (
            <React.Fragment>
                <Customers />
                <Route path={`/customer/:id`} component={Customer} />
            </React.Fragment>
        );
    }
}


// customers.jsx
import React, { Component } from 'react';
import { Link } from 'react-router-dom';

export default class Customers extends Component {
    state = {
        customers: []
    };

    render() {
        return (
            <React.Fragment>
                <header className="jumbotron"><h1>Customer List</h1></header>

                <div className="container">
                    <table className="table table-striped">
                        <thead>
                            <tr>
                                <th>Name</th>
                                <th>Address</th>
                            </tr>
                        </thead>
                        <tbody>
                            {this.state.customers.map(c => (<tr key={c.id}><td><Link to={`/customer/${c.id}`}>{c.name}</Link></td><td>{c.address}</td></tr>))}
                        </tbody>
                    </table>
                    <hr />
                </div>

                <footer className="footer">&copy; 2018</footer>
            </React.Fragment>
        );
    }

    async componentDidMount() {
        const result = await fetch('http://api.com/customers');
        const customers = await result.json();
        this.setState({ customers });
        console.log(this.state.customers);
    }
}


// customer.jsx
import React, { Component } from 'react';

export default class Customer extends Component {
    render() {
        return (<p>Customer</p>);
    };
}

App.js中添加Route（Route path = {/customer/:id} component = {Customer}）的行导致错误。如果我删除该行，我可以看到客户表，但只要我添加此行，然后我收到该错误消息。

我错过了这个路由器的工作原理吗？

谢谢。

UPDATE

将App.js更改为此非常简单的版本会导致错误

import React, { Component } from 'react';
import { Route } from 'react-router-dom/Route';

export default class App extends Component {
    state = {
    };

    render() {
        return (
            <div>
                <Route exact path='/' render={() => (<h1>Hello</h1>)} />
                <Route exact path='/customer' render={() => (<h1>Customer</h1>)} />
            </div>
        );
    }
}

完整的错误消息是：

元素类型无效：期望一个字符串（对于内置组件）或一个类/函数（对于复合组件）但得到：undefined。您可能忘记从其定义的文件中导出组件，或者您可能混淆了默认导入和命名导入。

Answer 1

改变这个：

import {Route} from "react-router-dom/Route";

对此：

import Route from "react-router-dom/Route";

直接访问时，Route是默认导出："react-router-dom/Route"从基础包导入Route时可以使用命名导出

import {Route} from "react-router-dom";

但不要混淆两者。

Answer 2

我觉得问题在于路径中的后退。你能尝试一下吗？

    render() {
          return (
              <React.Fragment>
                   <Customers />
                   <Route path='/customer/:id' component={Customer} />
             </React.Fragment>
           );
      }

要么

    render() {
          return (
              <React.Fragment>
                   <Customers />
                   <Route path={'/customer/:id'} component={Customer} />
             </React.Fragment>
           );
      }

Answer 3

看起来你在Customer组件的render()方法中有语法错误，当你尝试使用/渲染它时会引起问题。

尝试以下修复：

export default class Customer extends Component {
    render() {
        return (<p> Customer</p>); // <-- remove the whitespace in 
                                   //     closing tag </p> like so
    };
}