现在我们也可以在React 16.8中使用钩子:

import React, { useState, useEffect } from 'react';

const App = () => {
  const [ spinner, setSpinner ] = useState(true);

  // It will be executed before rendering

  useEffect(() => {
    setTimeout(() => setSpinner(false), 1000)
  }, []);

  // [] means like componentDidMount

  return !spinner && <div>Your content</div>;
};

export default App;

如果有人正在为上述用例寻找一个插入式、零配置和零依赖的库，请尝试pace.js (https://codebyzach.github.io/pace/docs/)。

它自动挂钩事件(ajax, readyState，历史推送状态，js事件循环等)，并显示一个可定制的加载器。

与我们的react/relay项目合作良好(使用react-router, relay请求处理导航更改) (不是affliated;在我们的项目中使用了pace.js，它工作得很好)

只要在<div id="root"></div>标签内添加内容，你就应该很好了!

// Example:

<div id="root">
   <div id="pre-loader">
        <p>Loading Website...</p>
        <img src="/images/my-loader.gif" />
   </div>
</div>

一旦<App />被加载，React会自动忽略<div id="root">标签内的所有内容，用你实际的应用程序覆盖它!

我们的目标

当html页面被渲染时，立即显示一个转轮(在React加载时)，并在React准备好后隐藏它。

由于旋转器是在纯HTML/CSS中呈现的(在React域之外)，React不应该直接控制显示/隐藏过程，实现对React应该是透明的。

解决方案1 -:empty伪类

因为你把react渲染到一个DOM容器中- <div id="app"></div>，你可以在这个容器中添加一个旋转器，当react加载并渲染时，旋转器将消失。

You can't add a DOM element (a div for example) inside the react root, since React will replace the contents of the container as soon as ReactDOM.render() is called. Even if you render null, the content would still be replaced by a comment - <!-- react-empty: 1 -->. This means that if you want to display the loader while the main component mounts, data is loading, but nothing is actually rendered, a loader markup placed inside the container (<div id="app"><div class="loader"></div></div> for example) would not work.

一个解决方法是将spinner类添加到react容器中，并使用:empty伪类。旋转器将是可见的，只要没有任何东西被呈现到容器中(注释不算数)。一旦react渲染了注释以外的东西，加载器就会消失。

示例1

在这个例子中，你可以看到一个组件在准备好之前呈现为空。容器也是加载器- <div id="app" class="app"></div>，并且加载器的类只有在它为:空时才会工作(见代码中的注释):

class App extends React.Component { state = { loading: true }; componentDidMount() { // this simulates an async action, after which the component will render the content demoAsyncCall().then(() => this.setState({ loading: false })); } render() { const { loading } = this.state; if(loading) { // if your component doesn't have to wait for an async action, remove this block return null; // render null when app is not ready } return ( <div>I'm the app</div> ); } } function demoAsyncCall() { return new Promise((resolve) => setTimeout(() => resolve(), 2500)); } ReactDOM.render( <App />, document.getElementById('app') ); .loader:empty { position: absolute; top: calc(50% - 4em); left: calc(50% - 4em); width: 6em; height: 6em; border: 1.1em solid rgba(0, 0, 0, 0.2); border-left: 1.1em solid #000000; border-radius: 50%; animation: load8 1.1s infinite linear; } @keyframes load8 { 0% { transform: rotate(0deg); } 100% { transform: rotate(360deg); } } <script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.4.1/react.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.4.1/react-dom.js"></script> <div id="app" class="loader"></div> <!-- add class loader to container -->

示例2

使用:empty伪类来显示/隐藏选择器的一种变体是将spinner设置为应用容器的兄弟元素，并且只要容器为空，就使用相邻的兄弟组合子(+)显示它:

class App extends React.Component { state = { loading: true }; componentDidMount() { // this simulates an async action, after which the component will render the content demoAsyncCall().then(() => this.setState({ loading: false })); } render() { const { loading } = this.state; if(loading) { // if your component doesn't have to wait for async data, remove this block return null; // render null when app is not ready } return ( <div>I'm the app</div> ); } } function demoAsyncCall() { return new Promise((resolve) => setTimeout(() => resolve(), 2500)); } ReactDOM.render( <App />, document.getElementById('app') ); #app:not(:empty) + .sk-cube-grid { display: none; } .sk-cube-grid { width: 40px; height: 40px; margin: 100px auto; } .sk-cube-grid .sk-cube { width: 33%; height: 33%; background-color: #333; float: left; animation: sk-cubeGridScaleDelay 1.3s infinite ease-in-out; } .sk-cube-grid .sk-cube1 { animation-delay: 0.2s; } .sk-cube-grid .sk-cube2 { animation-delay: 0.3s; } .sk-cube-grid .sk-cube3 { animation-delay: 0.4s; } .sk-cube-grid .sk-cube4 { animation-delay: 0.1s; } .sk-cube-grid .sk-cube5 { animation-delay: 0.2s; } .sk-cube-grid .sk-cube6 { animation-delay: 0.3s; } .sk-cube-grid .sk-cube7 { animation-delay: 0s; } .sk-cube-grid .sk-cube8 { animation-delay: 0.1s; } .sk-cube-grid .sk-cube9 { animation-delay: 0.2s; } @keyframes sk-cubeGridScaleDelay { 0%, 70%, 100% { transform: scale3D(1, 1, 1); } 35% { transform: scale3D(0, 0, 1); } } <script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.4.1/react.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.4.1/react-dom.js"></script> <div id="app"></div> <!-- add class loader to container --> <div class="sk-cube-grid"> <div class="sk-cube sk-cube1"></div> <div class="sk-cube sk-cube2"></div> <div class="sk-cube sk-cube3"></div> <div class="sk-cube sk-cube4"></div> <div class="sk-cube sk-cube5"></div> <div class="sk-cube sk-cube6"></div> <div class="sk-cube sk-cube7"></div> <div class="sk-cube sk-cube8"></div> <div class="sk-cube sk-cube9"></div> </div>

解决方案2 -传递旋转器“处理程序”作为道具

要对旋转器显示状态进行更细粒度的控制，可以创建两个函数showSpinner和hideSpinner，并通过props将它们传递给根容器。这些函数可以操作DOM，或者执行控制旋转器所需的任何操作。通过这种方式，React不知道“外部世界”，也不需要直接控制DOM。你可以很容易地替换函数进行测试，或者如果你需要改变逻辑，你可以将它们传递给React树中的其他组件。

示例1

const loader = document.querySelector('.loader'); // if you want to show the loader when React loads data again const showLoader = () => loader.classList.remove('loader--hide'); const hideLoader = () => loader.classList.add('loader--hide'); class App extends React.Component { componentDidMount() { this.props.hideLoader(); } render() { return ( <div>I'm the app</div> ); } } // the setTimeout simulates the time it takes react to load, and is not part of the solution setTimeout(() => // the show/hide functions are passed as props ReactDOM.render( <App hideLoader={hideLoader} showLoader={showLoader} />, document.getElementById('app') ) , 1000); .loader { position: absolute; top: calc(50% - 4em); left: calc(50% - 4em); width: 6em; height: 6em; border: 1.1em solid rgba(0, 0, 0, 0.2); border-left: 1.1em solid #000000; border-radius: 50%; animation: load8 1.1s infinite linear; transition: opacity 0.3s; } .loader--hide { opacity: 0; } @keyframes load8 { 0% { transform: rotate(0deg); } 100% { transform: rotate(360deg); } } <script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.4.1/react.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.4.1/react-dom.js"></script> <div id="app"></div> <div class="loader"></div>

例2 -钩子

本例使用useEffect钩子在组件挂载后隐藏旋转器。

const { useEffect } = React; const loader = document.querySelector('.loader'); // if you want to show the loader when React loads data again const showLoader = () => loader.classList.remove('loader--hide'); const hideLoader = () => loader.classList.add('loader--hide'); const App = ({ hideLoader }) => { useEffect(hideLoader, []); return ( <div>I'm the app</div> ); } // the setTimeout simulates the time it takes react to load, and is not part of the solution setTimeout(() => // the show/hide functions are passed as props ReactDOM.render( <App hideLoader={hideLoader} showLoader={showLoader} />, document.getElementById('app') ) , 1000); .loader { position: absolute; top: calc(50% - 4em); left: calc(50% - 4em); width: 6em; height: 6em; border: 1.1em solid rgba(0, 0, 0, 0.2); border-left: 1.1em solid #000000; border-radius: 50%; animation: load8 1.1s infinite linear; transition: opacity 0.3s; } .loader--hide { opacity: 0; } @keyframes load8 { 0% { transform: rotate(0deg); } 100% { transform: rotate(360deg); } } <script crossorigin src="https://unpkg.com/react@16/umd/react.development.js"></script> <script crossorigin src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script> <div id="app"></div> <div class="loader"></div>

你可以通过在react中使用惰性加载轻松做到这一点。 为此你必须使用惰性和悬疑反应。

import React, { lazy, Suspense } from 'react';

const loadable = (importFunc, { fallback = null } = { fallback: null }) => {
  const LazyComponent = lazy(importFunc);

  return props => (
    <Suspense fallback={fallback}>
      <LazyComponent {...props} />
    </Suspense>
  );
};

export default loadable;

然后像这样导出你的组件。

export const TeacherTable = loadable(() =>
  import ('./MainTables/TeacherTable'), {
    fallback: <Loading />,
  });

然后在你的路由文件中像这样使用它。

 <Route exact path="/app/view/teachers" component={TeacherTable} />

这就是现在你很好去每次你的DOM渲染你的加载组件将显示为我们已经在上面的fallback属性中指定。只要确保你只在componentDidMount()中做任何ajax请求

你不需要那么多的努力，这里有一个基本的例子。

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="utf-8" />
  <link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico" />
  <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
  <meta name="theme-color" content="#000000" />
  <meta name="description" content="Web site created using create-react-app" />
  <link rel="apple-touch-icon" href="logo192.png" />
  <link rel="manifest" href="%PUBLIC_URL%/manifest.json" />
  <title>Title</title>
  <style>
    body {
      margin: 0;
    }

    .loader-container {
      width: 100vw;
      height: 100vh;
      display: flex;
      overflow: hidden;
    }

    .loader {
      margin: auto;
      border: 5px dotted #dadada;
      border-top: 5px solid #3498db;
      border-radius: 50%;
      width: 100px;
      height: 100px;
      -webkit-animation: spin 2s linear infinite;
      animation: spin 2s linear infinite;
    }

    @-webkit-keyframes spin {
      0% {
        -webkit-transform: rotate(0deg);
      }

      100% {
        -webkit-transform: rotate(360deg);
      }
    }

    @keyframes spin {
      0% {
        transform: rotate(0deg);
      }

      100% {
        transform: rotate(360deg);
      }
    }

  </style>
</head>

<body>
  <noscript>You need to enable JavaScript to run this app.</noscript>
  <div id="root">
    <div class="loader-container">
      <div class="loader"></div>
    </div>
  </div>
</body>

</html>

您可以使用HTML和CSS使其看起来像您的示例。