反应-显示加载屏幕，而DOM是渲染?

这是一个来自谷歌Adsense应用页面的例子。加载界面显示在主界面之前。

我不知道如何用React做同样的事情，因为如果我用React组件渲染加载屏幕，它不会在页面加载时显示，因为它必须等待DOM渲染之前。

更新:

我通过将屏幕加载器放在index.html中并在React componentDidMount()生命周期方法中删除它来举例说明我的方法。

示例和反应加载屏幕。

当前回答

The starting of react app is based on the main bundle download. React app only starts after the main bundle being downloaded in the browser. This is even true in case of lazy loading architecture. But the fact is we cannot exactly state the name of any bundles. Because webpack will add a hash value at the end of each bundle at the time when you run 'npm run build' command. Of course we can avoid that by changing hash settings, but it will seriously affect the cache data problem in the Browser. Browsers might not take the new version because of the same bundle name. . we need a webpack + js + CSS approach to handle this situation.

更改public/index.html如下所示

<!DOCTYPE html> <html lang="en" xml:lang="en"> <head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width, initial-scale=1,maximum-scale=3.0, shrink-to-fit=no"> <meta name="theme-color" content="#000000">  <link rel="manifest" href="%PUBLIC_URL%/manifest.json"> <link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico"> <style> .percentage { position: absolute; top: 50%; left: 50%; width: 150px; height: 150px; border: 1px solid #ccc; background-color: #f3f3f3; -webkit-transform: translate(-50%, -50%); -ms-transform: translate(-50%, -50%); transform: translate(-50%, -50%); border: 1.1em solid rgba(0, 0, 0, 0.2); border-radius: 50%; overflow: hidden; display: -webkit-box; display: -ms-flexbox; display: flex; -webkit-box-pack: center; -ms-flex-pack: center; justify-content: center; -webkit-box-align: center; -ms-flex-align: center; align-items: center; } .innerpercentage { font-size: 20px; } </style> <script> function showPercentage(value) { document.getElementById('percentage').innerHTML = (value * 100).toFixed() + "%"; } var req = new XMLHttpRequest(); req.addEventListener("progress", function (event) { if (event.lengthComputable) { var percentComplete = event.loaded / event.total; showPercentage(percentComplete) // ... } else { document.getElementById('percentage').innerHTML = "Loading.."; } }, false); // load responseText into a new script element req.addEventListener("load", function (event) { var e = event.target; var s = document.createElement("script"); s.innerHTML = e.responseText; document.documentElement.appendChild(s); document.getElementById('parentDiv').style.display = 'none'; }, false); var bundleName = "<%= htmlWebpackPlugin.files.chunks.main.entry %>"; req.open("GET", bundleName); req.send(); </script>  <title>App Name</title> <link href="<%= htmlWebpackPlugin.files.chunks.main.css[0] %>" rel="stylesheet"> </head> <body> <noscript> You need to enable JavaScript to run this app. </noscript> <div id="parentDiv" class="percentage"> <div id="percentage" class="innerpercentage">loading</div> </div> <div id="root"></div>  </body> </html>

在你的webpack产品配置中，将HtmlWebpackPlugin选项改为如下

 new HtmlWebpackPlugin({
          inject: false,
...

您可能需要使用'eject'命令来获取配置文件。最新的webpack可能有选项配置HtmlWebpackPlugin而不弹出项目。

2019-07-18 11:52:02

其他回答

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;

2019-04-05 15:38:06

来自React文档，源代码。

React.lazy function lets you render a dynamic import as a regular component. This will automatically load the bundle containing the OtherComponent when this component is first rendered. React.lazy takes a function that must call a dynamic import(). This must return a Promise which resolves to a module with a default export containing a React component. The lazy component should then be rendered inside a Suspense component, which allows us to show some fallback content (such as a loading indicator) while we’re waiting for the lazy component to load.

import React, { Suspense } from 'react';

const OtherComponent = React.lazy(() => import('./OtherComponent'));

function MyComponent() {
  return (
    <div>
      <Suspense fallback={<div>Loading...</div>}>
        <OtherComponent />
      </Suspense>
    </div>
  );
}

回退道具接受你想渲染的任何React元素在等待组件加载时。你可以设置悬念组件位于惰性组件之上。你甚至可以包裹多个惰性组件和一个悬疑组件。

源

2022-05-20 16:36:15

这将发生在ReactDOM.render()控制根目录<div>之前。也就是说，你的应用程序到那时还没有被安装。

所以你可以把你的加载器添加到index.html文件的根目录<div>。在React接管之前，这将在屏幕上可见。

您可以使用任何最适合您的加载器元素(例如带有动画的svg)。

您不需要在任何生命周期方法上删除它。React会用你渲染的<App/>替换它的根<div>的所有子元素，就像我们在下面的动图中看到的那样。

关于CodeSandbox的例子

index . html

<head>
  <style>
    .svgLoader {
      animation: spin 0.5s linear infinite;
      margin: auto;
    }
    .divLoader {
      width: 100vw;
      height: 100vh;
      display: flex;
      align-items: center;
      justify-content: center;
    }
    @keyframes spin {
      0% { transform: rotate(0deg); }
      100% { transform: rotate(360deg); }
    }
  </style>
</head>

<body>
  <div id="root">
    <div class="divLoader">
      <svg class="svgLoader" viewBox="0 0 1024 1024" width="10em" height="10em">
        <path fill="lightblue"
          d="PATH FOR THE LOADER ICON"
        />
      </svg>
    </div>
  </div>
</body>

index.js

在ReactDOM.render()运行之前，使用调试器检查页面。

import React from "react";
import ReactDOM from "react-dom";
import "./styles.css";

function App() {
  return (
    <div className="App">
      <h1>Hello CodeSandbox</h1>
      <h2>Start editing to see some magic happen!</h2>
    </div>
  );
}

debugger; // TO INSPECT THE PAGE BEFORE 1ST RENDER

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

2019-05-08 18:19:32

这个问题可以通过React的lazy特性轻松解决。

import { Suspense, lazy } from "react"
import Loading from "components/Loading"

const Dashboard = lazy(() => import("containers/Dashboard"))

const App = () => (
  <Suspense fallback={<Loading />}>
    <Dashboard />
  </Suspense>
)

export default App

当仪表板组件仍在加载时，加载组件将显示出来。

2021-10-01 09:28:41

我不知道现在回答是否太晚，因为你可能已经找到了解决方案，但这里有一个来自我的观点，因为这个问题真的很有用。：我在scrimba.com上上了一堂课，在这里，老师从课堂开始，然后开始讲课。他通过课堂和状态来教授API调用。这是他的代码:

import React, {Component} from "react"

class App extends Component {
    constructor() {
        super()
        this.state = {
            loading: false,
            character: {}
        }
    }
    
    componentDidMount() {
        this.setState({loading: true})
        fetch("https://swapi.dev/api/people/1/")
            .then(response => response.json())
            .then(data => {
                this.setState({
                    loading: false,
                    character: data
                })
            })
    }
    
    render() {
        const text = this.state.loading ? "loading..." : this.state.character.name
        return (
            <div>
                <p>{text}</p>
            </div>
        )
    }
}

export default App

这很直接，在开始时将加载状态设置为true并保持它，直到接收到数据，然后当接收到数据时，更改状态并将加载设置为false并显示内容。现在我试着用钩子，作为练习，它工作得很顺利!一个简单而有效的解决方案。这是我的代码:

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

function App()
{
    const [response, setResponse] = useState([]);
    
    const [loading, setLoading] = useState(true);

    useEffect(() => {
        fetchResponse() ;
    } , []);

    const fetchResponse = async () => {
        const data = await fetch("https://swapi.dev/api/people/1/");
        const response = await data.json();

        setResponse(response);
        console.log(response.name);
        setLoading(false);
    } 

        const content = loading ? <i className="fas fa-atom fa-spin"></i> : <h1>{response.name}</h1>

    return(
        <section id="w-d-p">
            {content}
        </section>
    )
}

export default App;

钩子也是一样的逻辑。在数据加载时，我得到了漂亮的转轮然后，我的数据!

哦，顺便说一下，如果你不喜欢这个XD，你可以在fetch中放入自己的API。

2021-09-14 07:01:42

反应-显示加载屏幕，而DOM是渲染?

推荐文章

最新文章

标签