React-2----react基础

我会带着你远行 2023-06-19 11:25 24阅读 0赞

### 1 认识 ###

由facebook开发，只提供了MVC中的V。

优势：

①是组件化的，将js与html标签结合到一起

②单向数据流

③虚拟DOM树

下面为一段代码，初步认识react

<!DOCTYPE html>
    <html lang="zh">
    <head>
    	<meta charset="UTF-8">
    	<meta name="viewport" content="width=device-width, initial-scale=1.0">
    	<meta http-equiv="X-UA-Compatible" content="ie=edge">
    	<title></title>
    </head>
    <body>
    	<div id="app">
    		
    	</div>
    	<script type="text/babel">
    		class HelloMessage extends React.Component {
    		  render() {
    		    return (
    		      <div>
    		        Hello {this.props.name}
    		      </div>
    		    );
    		  }
    		}
    		
    		ReactDOM.render(
    		  <HelloMessage name="Taylor" />,
    		  document.getElementById('app')
    		);
    	</script>
    	<script src="https://cdn.bootcss.com/react/16.10.2/umd/react.development.js"></script>
    	<script src="https://cdn.bootcss.com/react-dom/16.10.2/umd/react-dom.development.js"></script>
    	<script src="https://cdn.bootcss.com/babel-standalone/7.0.0-beta.3/babel.js"></script>
    </body>
    </html>

### 2 create-react-app ###

有以下几个步骤

> npm install -g create-react-app

> create-react-app my-app

> cd my-app
> 
> npm start

也可以打包

> yarn build

### 3 第一个组件 ###

首先引入bootstrap,在index.html里面

> <link href="https://cdn.bootcss.com/twitter-bootstrap/4.0.0-beta.2/css/bootstrap.css" rel="stylesheet">

然后在App.js里面写代码

import React,{Component} from 'react';
    import logo from './logo.svg';
    import './App.css';
    
    class App extends Component {
    	render(){
    		return (
    			<div className="container">
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    				      <h1>hello world</h1>
    				   </div>
    			   </div>
    			</div>
    		)
    	}
    }
    
    
    export default App;

### 4 剩下的内容 ###

在src下新建一个components的目录，然后把组件都放到里边。我们新建一个header.js和home.js,内容分别为

import React,{Component} from 'react';
    
    
    class header extends Component {
    	render(){
    		return (
    			<div className="container">
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    				      <h1>header</h1>
    				   </div>
    			   </div>
    			</div>
    		)
    	}
    }
    
    
    export default header;

import React,{Component} from 'react';
    
    class home extends Component {
    	render(){
    		return (
    			<div className="container">
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    				      <h1>home</h1>
    				   </div>
    			   </div>
    			</div>
    		)
    	}
    }
    
    
    export default home;

然后在app.js里引用

import React,{Component} from 'react';
    import Header from './components/header.js'
    import Home from './components/home.js'
    
    class App extends Component {
    	render(){
    		let content='';
    		if(true){
    		   content='hello'	
    		}
    		return (
    			<div className="container">
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    					  <Header/>
    				   </div>
    			   </div>
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    				      <h1>hello world</h1>
    				   </div>
    			   </div>
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    					  <Home/>
    					  {content}
    					  {true ? 'hello':'world'}
    				   </div>
    			   </div>
    			</div>
    		)
    	}
    }
    
    
    export default App;

动态数据:\{\}里面可以用三元运算符

**props父组件向子组件传参和类型检查：**

App.js

import React,{Component} from 'react';
    import Header from './components/header.js'
    import Home from './components/home.js'
    
    class App extends Component {
    	render(){
    		let content='';
    		if(true){
    		   content='hello'	
    		}
    		const user={
    			name:'Anna',
    			hobbies:["sports","read"]
    		}
    		return (
    			<div className="container">
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    					  <Header/>
    				   </div>
    			   </div>
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    				      <h1>hello world</h1>
    				   </div>
    			   </div>
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    					  <Home name={"Max"} age={12} user={user}>
    					     <p>I am child</p>
    					  </Home>
    					  {content}
    					  {true ? 'hello':'world'}
    				   </div>
    			   </div>
    			</div>
    		)
    	}
    }
    
    
    export default App;

home.js

import React,{Component} from 'react';
    import ProTypes from 'prop-types';
    
    class home extends Component {
    	render(){
    		console.log(this.props);
    		return (
    			<div className="container">
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    				      <div>name:{this.props.name}</div>
    					  <div>age:{this.props.age}</div>
    					  <h4>hobbies</h4>
    					  <ul>
    					    {this.props.user.hobbies.map((hobby)=><li key={hobby}>{hobby}</li>)}
    					  </ul>
    					  <div>{this.props.children}</div>
    				   </div>
    			   </div>
    			</div>
    		)
    	}
    }
    
    // 检验数据类型
    home.propTypes={
    	name:ProTypes.string,
    	age:ProTypes.number,
    	user:ProTypes.object,
    	children:ProTypes.element.isRequired
    }
    
    export default home;

**state:更新DOM,只是部分渲染**

import React,{Component} from 'react';
    import ProTypes from 'prop-types';
    
    class home extends Component {
    	constructor(props){
    		super(props);
    		this.state={
    			age:props.age
    		}
    	}
    	
    	onMakeMe(){
    		this.setState({
    			age:this.state.age + 1
    		})
    	}
    	
    	render(){
    		console.log(this.props);
    		return (
    			<div className="container">
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    				      <div>name:{this.props.name}</div>
    					  <div>age:{this.state.age}</div>,
    					  <h4>hobbies</h4>
    					  <ul>
    					    {this.props.user.hobbies.map((hobby)=><li key={hobby}>{hobby}</li>)}
    					  </ul>
    					  <div>{this.props.children}</div>
    					  
    					  <button onClick={()=>{this.onMakeMe()}} className="btn btn-primary">click me</button>
    					  
    				   </div>
    			   </div>
    			</div>
    		)
    	}
    }
    
    // 检验数据类型
    home.propTypes={
    	name:ProTypes.string,
    	age:ProTypes.number,
    	user:ProTypes.object,
    	children:ProTypes.element.isRequired
    }
    
    export default home;

**无状态组件：又叫函数式组件，指无状态改变的组件，没有生命周期**

import React from 'react';
    
    // 第一种写法
    // class header extends Component {
    // 	render{
    // 		return (
    // 			<div className="container">
    // 			   <div className="row">
    // 				   <div className="col-xs-1 col-xs-offset-11">
    // 					  <h1>header</h1>
    // 				   </div>
    // 			   </div>
    // 			</div>
    // 		)
    // 	}
    // }
    
    // 第二种写法,一般适用于无需state,即不需要处理用户的输入和不需要用到生命周期函数
    //好处:1 不需要声明类,可以避免大量的比如extends和constructor的代码
    //     2 不需要声明this关键字
    const header = (props)=> {
    	return (
    		<div className="container">
    		   <div className="row">
    			   <div className="col-xs-1 col-xs-offset-11">
    				  <h1>header</h1>
    			   </div>
    		   </div>
    		</div>
    	)
    }
    
    
    export default header;

如果后续又想改成有状态的组件，可以改。以后学。

**子组件向父组件传参：**

子组件：

import React,{Component} from 'react';
    import ProTypes from 'prop-types';
    
    class home extends Component {
    	handleGreet(){
    		this.props.greet(this.state.age)
    	}
    	
    	render(){
    		console.log(this.props);
    		return (
    			<div className="container">
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    					  
    					  <button onClick={this.props.greet} className="btn btn-primary">greet</button>
    					  <button onClick={this.handleGreet.bind(this)} className="btn btn-primary">handlegreet</button>
    				   </div>
    			   </div>
    			</div>
    		)
    	}
    }
    
    export default home;

父组件：

import React,{Component} from 'react';
    import Header from './components/header.js'
    import Home from './components/home.js'
    
    class App extends Component {
    	onGreet(age){
    		alert("hello!"+age)
    	}
    	
    	render(){
    		return (
    			<div className="container">
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    					  <Header/>
    				   </div>
    			   </div>
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    				      <h1>hello world</h1>
    				   </div>
    			   </div>
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    					  <Home name={"Max"} age={12} user={user} greet={this.onGreet}>
    					     <p>I am child</p>
    					  </Home>
    					  {content}
    					  {true ? 'hello':'world'}
    				   </div>
    			   </div>
    			</div>
    		)
    	}
    }
    
    
    export default App;

**兄弟组件间传值和数据双向绑定、生命周期**

app.js

import React,{Component} from 'react';
    import Header from './components/header.js'
    import Home from './components/home.js'
    
    class App extends Component {
    	constructor(){
    		super();
    		this.state={
    			homeLink:'Home',
    			homeMounted:true
    		}
    	}
    	
    	onGreet(age){
    		alert("hello!"+age)
    	}
    	
    	onChangeLinkName(newName){
    		this.setState({
    			homeLink:newName
    		})
    	}
    	
    	onChangeHomeMounted(){
    		this.setState({
    			homeMounted:!this.state.homeMounted
    		})
    	}
    	
    	render(){
    		let content='';
    		if(true){
    		   content='hello'	
    		}
    		const user={
    			name:'Anna',
    			hobbies:["sports","read"]
    		}
    		
    		let homeCap="";
    		if(this.state.homeMounted){
    			homeCap=(
    			   <Home
    			     name={"Max"} 
    				 age={12} 
    				 user={user} g
    				 greet={this.onGreet}
    				 initialName={this.state.homeLink}
    				 changeLink={this.onChangeLinkName.bind(this)}>
    			      <p>I am child</p>
    			   </Home>);
    		}
    		return (
    			<div className="container">
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    					  <Header homeLink={this.state.homeLink}/>
    				   </div>
    			   </div>
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    				      <h1>hello world</h1>
    				   </div>
    			   </div>
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    				      {homeCap}
    					  {content}
    					  {true ? 'hello':'world'}
    				   </div>
    			   </div>
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    					  <button onClick={this.onChangeHomeMounted.bind(this)} className="btn btn-primary">component</button>
    				   </div>
    			   </div>
    			</div>
    		)
    	}
    }
    
    
    export default App;

home.js

import React,{Component} from 'react';
    import ProTypes from 'prop-types';
    
    class home extends Component {
    	constructor(props){
    		super(props);
    		this.state={
    			age:props.age,
    			homeLink:props.initialName
    		}
    	}
    	
    	onMakeMe(){
    		this.setState({
    			age:this.state.age + 1
    		})
    	}
    	
    	handleGreet(){
    		this.props.greet(this.state.age)
    	}
    	
    	onChangeLink(){
    		this.props.changeLink(this.state.homeLink)
    	}
    	
    	onHandleChange(event){
    		this.setState({
    			homeLink:event.target.value
    		})
    	}
    	
    	componentWillMount(){
    		console.log('will mount')
    	}
    	
    	componentDidMount(){
    		console.log('did mount')
    	}
    	
    	componentWillReceiveProps(nextProps){
    		console.log('will receive props',nextProps)
    	}
    	
    	shouldComponentUpdate(nextProps,nextState){
    		console.log('should upstate',nextProps,nextState)
    	}
    	
    	componentWillUpdate(nextProps,nextState){
    		console.log('will upstate',nextProps,nextState)
    	}
    	
    	componentDidUpdate(prevProps,prevState){
    		console.log('did upstate',prevProps,prevState)
    	}
    	
    	componentWillUnmount(){
    		console.log('will unmount')
    	}
    	
    	render(){
    		console.log(this.props);
    		return (
    			<div className="container">
    			   <div className="row">
    			       <div className="col-xs-1 col-xs-offset-11">
    				      <div>name:{this.props.name}</div>
    					  <div>age:{this.state.age}</div>,
    					  <h4>hobbies</h4>
    					  <ul>
    					    {this.props.user.hobbies.map((hobby)=><li key={hobby}>{hobby}</li>)}
    					  </ul>
    					  <div>{this.props.children}</div>
    					  
    					  <button onClick={()=>{this.onMakeMe()}} className="btn btn-primary">click me</button>
    					  
    					  <hr/>
    					  
    					  <button onClick={this.handleGreet.bind(this)} className="btn btn-primary">handlegreet</button>
    					  
    					  <hr/>
    					  <input 
    					    type="" 
    						defaultValue={this.props.initialName} 
    						value={this.state.initialName} 
    						onChange={(event)=>this.onHandleChange(event)}/
    					  >
    					  
    					  <button onClick={this.onChangeLink.bind(this)} className="btn btn-primary">Change Header Link</button>
    				   </div>
    			   </div>
    			</div>
    		)
    	}
    }
    
    // 检验数据类型
    home.propTypes={
    	name:ProTypes.string,
    	age:ProTypes.number,
    	user:ProTypes.object,
    	children:ProTypes.element.isRequired,
    	initialName:ProTypes.string
    }
    
    export default home;

header.js

import React from 'react';
    
    const header = (props)=> {
    	return (
    		<div className="container">
    		   <div className="row">
    			   <div className="col-xs-1 col-xs-offset-11">
    				  <h1>header----{props.homeLink}</h1>
    			   </div>
    		   </div>
    		</div>
    	)
    }
    
    
    export default header;

组件的生命周期可分成三个状态：

*  Mounting：已插入真实 DOM（1,2）
 *  Updating：正在被重新渲染（3,4,5,6）
 *  Unmounting：已移出真实 DOM（7）

生命周期的方法有：

*  **componentWillMount** 在渲染前调用,在客户端也在服务端。
 *  **componentDidMount** : 在第一次渲染后调用，只在客户端。之后组件已经生成了对应的DOM结构，可以通过this.getDOMNode()来进行访问。 如果你想和其他JavaScript框架一起使用，可以在这个方法中调用setTimeout, setInterval或者发送AJAX请求等操作(防止异步操作阻塞UI)。
 *  **componentWillReceiveProps** 在组件接收到一个新的 prop (更新后)时被调用。这个方法在初始化render时不会被调用。
 *  **shouldComponentUpdate** 返回一个布尔值。在组件接收到新的props或者state时被调用。在初始化时或者使用forceUpdate时不被调用。  
    可以在你确认不需要更新组件时使用。
 *  **componentWillUpdate**在组件接收到新的props或者state但还没有render时被调用。在初始化时不会被调用。
 *  **componentDidUpdate** 在组件完成更新后立即调用。在初始化时不会被调用。
 *  **componentWillUnmount**在组件从 DOM 中移除之前立刻被调用。