React useEffect 不会在路由更改时触发

Question

我希望console.log('Refresh')每次路由更改时都会运行（从 Component1 切换到 Component2）。但它仅在第一次渲染时触发。为什么？

index.js：

import React from 'react';
import ReactDOM from 'react-dom';
import App from './App';
import { BrowserRouter } from 'react-router-dom';

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

App.js：

import React, { useEffect } from 'react';
import { Switch, Route } from 'react-router-dom';
import Nav from './Nav';
import Component1 from './Component1';
import Component2 from './Component2';

const App = () => {

  useEffect( () => console.log('Refresh'));

  return (
        [<Switch>
            <Route                            component = {Nav}/>
        </Switch>,
        <Switch>
            <Route exact path = '/component1' component = {Component1}/>
            <Route exact path = '/component2' component = {Component2}/>
        </Switch>]
  );
}

export default App;

Nav.js：

import React from 'react';
import { Link } from 'react-router-dom';

const  Nav = () => {
  return (
    <div>
        <Link to = '/component1'>Component 1</Link>
        <Link to = '/component2'>Component 2</Link>
    </div>
  );
}

export default Nav;

Component1.js：

import React from 'react';

const  Component1 = () => {

  return (
    <div>
        <p>Hi</p>
    </div>
  );
}

export default Component1;

Component2.js：

import React from 'react';

const  Component2 = () => {
  return (
    <div>
        <p>Bye</p>
    </div>
  );
}

export default Component2;

Answer 1

该useEffect不会被触发，因为App组件没有重新渲染，没有在该组件（无状态或道具更新）改变。

如果你想让App组件在路由改变时重新渲染，你可以使用withRouterHOC 注入路由 props，如下所示：

import { Switch, Route, withRouter } from 'react-router-dom';

const App = () => {

  useEffect( () => console.log('Refresh'));

  return (...);
}

export default withRouter(App);

示例：https : //codesandbox.io/s/youthful-pare-n8p1y

Answer 2

使用 key 属性，所以每次我们渲染新组件时（不同的键）

<Route path='/mypath/:username' exact render= {routeProps =><MyCompo {...routeProps} key={document.location.href} />} />

Answer 3

使用 useEffect 的第二个参数来有条件地应用效果。例如通过react-router-dom，你可以获得一些属性

const { schoolId, classId } = props

useEffect(() => {
   // fetch something here
}, [schoolId, classId)

这里[schoolId, classId作为useEffect触发的唯一标识。

Answer 4

使用钩子：

使用useLocation 并useLayoutEffect获得更高的效率：

   import { useLocation } from "react-router-dom";
//...
   const location = useLocation();
//...
   useLayoutEffect(() => {
    console.log("location",location) 
    
   }, [location])