React基本知识点整理

React中引入样式的2种方式

1,内联样式

import React, { Component } from 'react'
export default class index extends Component {
  render() {
    return (
      <div>
        <div style={
  {color:"red",fontSize:"18px"}}>内联样式</div>
      </div>
    )
  }
}

2,声明式内联样式

import React, { Component } from 'react'
const styleCss={
  "font-size":"20px",
   color:"red"
}
export default class index extends Component {
  render() {
    return (
      <div>
        <div style={styleCss}>声明式内联样式</div>
      </div>
    )
  }
}

props参数传递（父传子）

//父组件
import React, { Component } from 'react'
import Child from './reac'
export default class index extends Component {
  state={
    data:[
        {id:"001",name:"张三"},
        {id:"002",name:"李四"},
        {id:"003",name:"王五"},
    ]
  }
  render() {
    return (
      <div>
        接受父组件传递过来的数据
        <Child data={this.state.data}></Child>
      </div>
    )
  }
}

//子组件
import React, { Component } from 'react'

export default class index extends Component {
  render() {
    console.log(this.props.data)
    return (
      <div>
        <ul>
          {
            this.props.data.map((item)=>{
              return <li key={item.id}>{item.name}</li>
            })
          }
        </ul>
      </div>
    )
  }
}

子组件传参给父组件（子传父）

//父组件
import React, { Component } from 'react'
import Child from './reac'
export default class index extends Component {
  state={
    name:""
  }
  getdata=(msg)=>{
    this.setState({
        name:msg
    })
  }
  render() {
    return (
      <div>
        接受子组件传递过来的数据{this.state.name}
        <Child getdata={this.getdata}></Child>
      </div>
    )
  }
}

//子组件
import React, { Component } from 'react'

export default class index extends Component {
  render() {
    return (
      <div>
        <button onClick={()=>{this.props.getdata("哈哈")}}>点击获取数据</button>
      </div>
    )
  }
}

路由组件传递params参数（父传子）

//父组件
import React, { Component } from 'react'
import {Link,Route} from 'react-router-dom'
import Detail from './Detail'

export default class Message extends Component {
	state = {
		messageArr:[
			{id:'01',title:'消息1'},
			{id:'02',title:'消息2'},
			{id:'03',title:'消息3'},
		]
	}
	render() {
		const {messageArr} = this.state
		return (
			<div>
				<ul>
					{
						messageArr.map((msgObj)=>{
							return (
								<li key={msgObj.id}>
									{/* 向路由组件传递params参数 */}
									<Link to={`/home/message/detail/${msgObj.id}/${msgObj.title}`}>{msgObj.title}</Link>
								</li>
							)
						})
					}
				</ul>
				<hr/>
				{/* 声明接收params参数 */}
				<Route path="/home/message/detail/:id/:title" component={Detail}/>
			</div>
		)
	}
}

//子组件
import React, { Component } from 'react'

const DetailData = [
	{id:'01',content:'张三'},
	{id:'02',content:'李四'},
	{id:'03',content:'王五'}
]
export default class Detail extends Component {
	render() {
		console.log(this.props);
		// 接收params参数
		const {id,title} = this.props.match.params
		const findResult = DetailData.find((detailObj)=>{
			return detailObj.id === id
		})
		return (
			<ul>
				<li>ID:{id}</li>
				<li>TITLE:{title}</li>
				<li>CONTENT:{findResult.content}</li>
			</ul>
		)
	}
}

路由组件传递search参数（父传子）

//父组件
import React, { Component } from 'react'
import {Link,Route} from 'react-router-dom'
import Detail from './Detail'

export default class Message extends Component {
	state = {
		messageArr:[
			{id:'01',title:'消息1'},
			{id:'02',title:'消息2'},
			{id:'03',title:'消息3'},
		]
	}
	render() {
		const {messageArr} = this.state
		return (
			<div>
				<ul>
					{
						messageArr.map((msgObj)=>{
							return (
								<li key={msgObj.id}>

									{/* 向路由组件传递search参数 */}
									<Link to={`/home/message/detail/?id=${msgObj.id}&title=${msgObj.title}`}>{msgObj.title}</Link>

								</li>
							)
						})
					}
				</ul>
				<hr/>

				{/* search参数无需声明接收，正常注册路由即可 */}
				<Route path="/home/message/detail" component={Detail}/>

			</div>
		)
	}
}

//子组件
import React, { Component } from 'react'
import qs from 'querystring'

const DetailData = [
	{id:'01',content:'张三'},
	{id:'02',content:'李四'},
	{id:'03',content:'王五'}
]
export default class Detail extends Component {
	render() {
		console.log(this.props);

		// 接收search参数
		const {search} = this.props.location
		const {id,title} = qs.parse(search.slice(1))

		const findResult = DetailData.find((detailObj)=>{
			return detailObj.id === id
		})
		return (
			<ul>
				<li>ID:{id}</li>
				<li>TITLE:{title}</li>
				<li>CONTENT:{findResult.content}</li>
			</ul>
		)
	}
}

路由组件传递state参数（父传子）

//父组件
import React, { Component } from 'react'
import {Link,Route} from 'react-router-dom'
import Detail from './Detail'

export default class Message extends Component {
	state = {
		messageArr:[
			{id:'01',title:'消息1'},
			{id:'02',title:'消息2'},
			{id:'03',title:'消息3'},
		]
	}
	render() {
		const {messageArr} = this.state
		return (
			<div>
				<ul>
					{
						messageArr.map((msgObj)=>{
							return (
								<li key={msgObj.id}>
									{/* 向路由组件传递state参数 */}
									<Link to={
  {pathname:'/home/message/detail',state:{id:msgObj.id,title:msgObj.title}}}>{msgObj.title}</Link>

								</li>
							)
						})
					}
				</ul>
				<hr/>
				{/* state参数无需声明接收，正常注册路由即可 */}
				<Route path="/home/message/detail" component={Detail}/>

			</div>
		)
	}
}

//子组件
import React, { Component } from 'react'
// import qs from 'querystring'

const DetailData = [
	{id:'01',content:'你好，中国'},
	{id:'02',content:'你好，尚硅谷'},
	{id:'03',content:'你好，未来的自己'}
]
export default class Detail extends Component {
	render() {
		console.log(this.props);
		// 接收state参数
		const {id,title} = this.props.location.state || {}

		const findResult = DetailData.find((detailObj)=>{
			return detailObj.id === id
		}) || {}
		return (
			<ul>
				<li>ID:{id}</li>
				<li>TITLE:{title}</li>
				<li>CONTENT:{findResult.content}</li>
			</ul>
		)
	}
}

路由的其本知识点（react-router6）

1,一级路由

//父元素
import React from 'react'
import {NavLink,Routes,Route} from 'react-router-dom'
import About from './pages/About'
import Home from './pages/Home'

export default function App() {
	return (
		<div>
			<div className="row">
				<div className="col-xs-offset-2 col-xs-8">
					<div className="page-header"><h2>React Router Demo</h2></div>
				</div>
			</div>
			<div className="row">
				<div className="col-xs-2 col-xs-offset-2">
					<div className="list-group">
						{/* 路由链接 */}
						<NavLink className="list-group-item" to="/about">About</NavLink>
						<NavLink className="list-group-item" to="/home">Home</NavLink>
					</div>
				</div>
				<div className="col-xs-6">
					<div className="panel">
						<div className="panel-body">
							{/* 注册路由 */}
							<Routes>
								<Route path="/about" element={<About/>}/>
								<Route path="/home" element={<Home/>}/>
							</Routes>
						</div>
					</div>
				</div>
			</div>
		</div>
	)
}

//两上要接受的子元素 about和Home
import React from 'react'

export default function About() {
	return (
		<h3>我是About的内容</h3>
	)
}

import React from 'react'

export default function Home() {
	return (
		<h3>我是Home的内容</h3>
	)
}

2,重定向

//父组件
import React from 'react'
import {NavLink,Routes,Route,Navigate} from 'react-router-dom'
import About from './pages/About'
import Home from './pages/Home'

export default function App() {
	return (
		<div>
			<div className="row">
				<div className="col-xs-offset-2 col-xs-8">
					<div className="page-header"><h2>React Router Demo</h2></div>
				</div>
			</div>
			<div className="row">
				<div className="col-xs-2 col-xs-offset-2">
					<div className="list-group">
						{/* 路由链接 */}
						<NavLink className="list-group-item" to="/about">About</NavLink>
						<NavLink className="list-group-item" to="/home">Home</NavLink>
					</div>
				</div>
				<div className="col-xs-6">
					<div className="panel">
						<div className="panel-body">
							{/* 注册路由 */}
							<Routes>
								<Route path="/ABOUT" element={<About/>}/>
								<Route path="/home" element={<Home/>}/>
								<Route path="/" element={<Navigate to="/about"/>}/>
							</Routes>
						</div>
					</div>
				</div>
			</div>
		</div>
	)
}

//about和home
import React from 'react'

export default function About() {
	return (
		<h3>我是About的内容</h3>
	)
}

import React,{useState} from 'react'
import {Navigate} from 'react-router-dom'

export default function Home() {
	const [sum,setSum] = useState(1)
	return (
		<div>
			<h3>我是Home的内容</h3>
			{sum === 2 ? <Navigate to="/about" replace={true}/> : <h4>当前sum的值是：{sum}</h4>}
			<button onClick={()=>setSum(2)}>点我将sum变为2</button>
		</div>
	)
}

3，react导航高亮

//父元素   这里的样式reactStyle需要提前声明

import React from 'react'
//引入路由
import {NavLink,Routes,Route,Navigate} from 'react-router-dom'
//引入组件
import About from './Pages/About'
import Home from './Pages/Home'

export default function App() {
  function computetClassStyle({isActive}){
    return isActive?'list-group-item reactStyle':'list-group-item'
  }
  return (
    <div>
      <div>
        <div className="row">
          <div className="col-xs-offset-2 col-xs-8">
            <div className="page-header"><h2>React Router Demo</h2></div>
          </div>
        </div>
        <div className="row">
          <div className="col-xs-2 col-xs-offset-2">
            <div className="list-group">
              <NavLink className={computetClassStyle} to="about">About</NavLink>
              <NavLink className={computetClassStyle} to="/home">Home</NavLink>
            </div>
          </div>
          <div className="col-xs-6">
            <div className="panel">
              <div className="panel-body">
                <h3>新路由</h3>
                {/* 注册路由 */}
                <Routes>
                  <Route path='/About' element={<About></About>}></Route>
                  <Route path='/Home' element={<Home></Home>}></Route>
                  <Route path='/' element={<Navigate to="/About"></Navigate>}></Route>
                </Routes>
              </div>
            </div>
          </div>
        </div>
      </div>
    </div>
  )
}



//两上要接受的子元素 about和Home
import React from 'react'

export default function About() {
	return (
		<h3>我是About的内容</h3>
	)
}

import React from 'react'

export default function Home() {
	return (
		<h3>我是Home的内容</h3>
	)
}

4,路由的统一管理

//在主文件中使用
import React from 'react'
//引入路由
import {NavLink,useRoutes} from 'react-router-dom'
import router from './router'

export default function App() {
  //路由表的使用
  const element=useRoutes(router)
  return (
    <div>
      <div>
        <div className="row">
          <div className="col-xs-offset-2 col-xs-8">
            <div className="page-header"><h2>React Router Demo</h2></div>
          </div>
        </div>
        <div className="row">
          <div className="col-xs-2 col-xs-offset-2">
            <div className="list-group">
              <NavLink className="list-group-item" to="about">About</NavLink>
              <NavLink className="list-group-item" to="/home">Home</NavLink>
            </div>
          </div>
          <div className="col-xs-6">
            <div className="panel">
              <div className="panel-body">
                <h3>新路由</h3>
                {/* 注册路由 */}
                {element}
              </div>
            </div>
          </div>
        </div>
      </div>
    </div>
  )
}

//router中的路由列表
import Home from "../Pages/Home"
import About from "../Pages/About"
import { Navigate } from "react-router-dom"
export default [
    {
        path:'/about',
        element:<About></About>
    },
    {
        path:'/Home',
        element:<Home></Home>
    },
    {
        path:'/',
        element:<Navigate to="/about"></Navigate>
    }
]

5,路由的嵌套,父里面包含子

6,search传递参数

//参数传递组件
import React,{useState} from 'react'
import { Link,Outlet } from 'react-router-dom'

export default function Message() {
  const [message] =useState([
	{id:'001',title:'张三',content:'kdjfkdfj'},
	{id:'002',title:'李四',content:'45612'},
	{id:'003',title:'王五',content:'kdjferetdkdfj'},
	{id:'004',title:'赵六',content:'kdjadffkdfj'}
  ])
  return (
    <div>
      <ul>
		{
			message.map((m)=>{
				return (
					<li key={m.id}>
						{/* 使用search带参数 */}
						<Link to={`detail?id=${m.id}&title=${m.title}&content=${m.content}`}>{m.title}</Link>
					</li>
				)
			})
		}			
	 </ul>
	 {/* 规定路由展示的位置 */}
	 <Outlet></Outlet>
    </div>
  )
}

//参数接收组件
import React from 'react'
import { useSearchParams } from 'react-router-dom'

export default function Detail() {
  const [search]=useSearchParams()
  console.log(search.get('id'))
  const id=search.get('id')
  const title=search.get('title')
  const content=search.get('content')
  return (
    <div>
      <ul>
        <li>{id}</li>
        <li>{title}</li>
        <li>{content}</li>
      </ul>
    </div>
  )
}

7,state传递参数

//传递组件
import React,{useState} from 'react'
import { Link,Outlet } from 'react-router-dom'

export default function Message() {
  const [message] =useState([
	{id:'001',title:'张三',content:'kdjfkdfj'},
	{id:'002',title:'李四',content:'45612'},
	{id:'003',title:'王五',content:'kdjferetdkdfj'},
	{id:'004',title:'赵六',content:'kdjadffkdfj'}
  ])
  return (
    <div>
      <ul>
		{
			message.map((m)=>{
				return (
					<li key={m.id}>
						{/* 使用state带参数 state里面需要包含一个对象*/}
						<Link to="detail" state={
  {
							id:m.id,
							title:m.title,
							content:m.content
						}}>{m.title}</Link>
					</li>
				)
			})
		}			
	 </ul>
	 {/* 规定路由展示的位置 */}
	 <Outlet></Outlet>
    </div>
  )
}

//接受组件
import React from 'react'
//需要使用useLocation
import { useLocation } from 'react-router-dom'

export default function Detail() {

  const {state:{id,title,content}}=useLocation()
  return (
    <div>
      <ul>
        <li>{id}</li>
        <li>{title}</li>
        <li>{content}</li>
      </ul>
    </div>
  )
}

8,编程式路由导航

//传递组件
import React,{useState} from 'react'
import { Link,Outlet,useNavigate } from 'react-router-dom'

export default function Message() {
  const [message] =useState([
	{id:'001',title:'张三',content:'kdjfkdfj'},
	{id:'002',title:'李四',content:'45612'},
	{id:'003',title:'王五',content:'kdjferetdkdfj'},
	{id:'004',title:'赵六',content:'kdjadffkdfj'}
  ])
  //编辑式路由导航，需要借助useNavigate
  //2,useNavigate还可以实现前进和后退 传入对应的参数即可
  const Nav=useNavigate()
  function showDetail(m){
	Nav('Detail',{
		replace:false,
		state:{
			id:m.id,
			title:m.title,
			content:m.content
		}
	})
  }
  return (
    <div>
      <ul>
		{
			message.map((m)=>{
				return (
					<li key={m.id}>
						{/* 使用state带参数 state里面需要包含一个对象*/}
						<Link to="detail" state={
  {
							id:m.id,
							title:m.title,
							content:m.content
						}}>{m.title}</Link>
						<button onClick={()=>showDetail(m)}>查看详情</button>
					</li>
				)
			})
		}			
	 </ul>
	 {/* 规定路由展示的位置 */}
	 <Outlet></Outlet>
    </div>
  )
}

//接受组件
import React from 'react'
//需要使用useLocation
import { useLocation } from 'react-router-dom'

export default function Detail() {

  const {state:{id,title,content}}=useLocation()
  return (
    <div>
      <ul>
        <li>{id}</li>
        <li>{title}</li>
        <li>{content}</li>
      </ul>
    </div>
  )
}

setState更新状态的2种写法

(1). setState(stateChange, [callback])------对象式的setState
            1.stateChange为状态改变对象(该对象可以体现出状态的更改)
            2.callback是可选的回调函数, 它在状态更新完毕、界面也更新后(render调用后)才被调用
                    
    (2). setState(updater, [callback])------函数式的setState
            1.updater为返回stateChange对象的函数。
            2.updater可以接收到state和props。
            4.callback是可选的回调函数, 它在状态更新、界面也更新后(render调用后)才被调用。
总结:
        1.对象式的setState是函数式的setState的简写方式(语法糖)
        2.使用原则：
                (1).如果新状态不依赖于原状态 ===> 使用对象方式
                (2).如果新状态依赖于原状态 ===> 使用函数方式
                (3).如果需要在setState()执行后获取最新的状态数据, 
                    要在第二个callback函数中读取

//父组件 App.js
//import logo from './logo.svg';
import React, { Component } from 'react'
import './App.css'
import SetStateA from './components/SetState1'

export default class App extends Component{
 
  render(){
    return(
      <div>
		    <SetStateA></SetStateA>
	  </div>
    )
  }
}


//子组件 components
import React, { Component } from 'react'

export default class SetStateA extends Component {
  //对象式的setState
  state={count:0}
  add=()=>{
    //获取原来count的值
    const {count}=this.state
    //更新状态
    this.setState({count:count+1},()=>{
        console.log('监测值的改变'+this.state.count)
    })
  }
  //函数式的写法
  addNum=()=>{
    this.setState((state,props)=>{
        console.log(props)
        return {count:state.count+1}
    })
  }
  render() {
    return (
      <div>
        <h1>当前求和为{this.state.count}</h1>
        <button onClick={this.add}>对象式</button>
        <button onClick={this.addNum}>函数式</button>
      </div>
    )
  }
}

路由组件的lazyLoad

1，lazyLoad主要用于大量路由切换的时候，根据需要加载对应的路由信息

2，通过React的lazy函数配合import()函数动态加载路由组件 ===> 路由组件代码会被分开打包

3，通过<Suspense>指定在加载得到路由

//在父组件App.js中引入子组件
//import logo from './logo.svg';
import React, { Component } from 'react'
import './App.css'
import Lazyload from './components/Layload'

export default class App extends Component{
  render(){
    return(
      <div>
        <Lazyload></Lazyload>
	  </div>
    )
  }
}
//lazyload组件里面包含两个子组件home和about
import React, { Component,lazy,Suspense } from 'react'
import {NavLink,Route} from 'react-router-dom'
//以前的加载方式
// import Home from './Home'
// import About from './About'

//使用lazy
const Home=lazy(()=>import('./Home'))
const About =lazy(()=>import('./About'))

export default class Lazyload extends Component {
	render() {
		return (
			<div>
				<div className="row">
					<div className="col-xs-offset-2 col-xs-8">
						<div className="page-header"><h2>React Router</h2></div>
					</div>
				</div>
				<div className="row">
					<div className="col-xs-2 col-xs-offset-2">
						<div className="list-group">

							{/* 在React中靠路由链接实现切换组件--编写路由链接 */}
							<NavLink className="list-group-item" to="/About">About</NavLink>
							<NavLink className="list-group-item" to="/Home">Home</NavLink>
						</div>
					</div>
					<div className="col-xs-6">
						<div className="panel">
							<div className="panel-body">
								{/* 注册路由 */}
                                <Suspense fallback={<h1>正在加载中......</h1>}>
                                    <Route path="/About" component={About}/>
                                    <Route path="/Home" component={Home}/>
                                </Suspense>
							</div>
						</div>
					</div>
				</div>
			</div>
		)
	}
}

//about和home两个子组件中的内容
//about
import React, { Component } from 'react'

export default class About extends Component {
  render() {
    return (
      <div>
        About
      </div>
    )
  }
}
//home
import React, { Component } from 'react'

export default class Home extends Component {
  render() {
    return (
      <div>
        Home
      </div>
    )
  }
}

State Hook

(1). State Hook让函数组件也可以有state状态, 并进行状态数据的读写操作
(2). 语法: const [xxx, setXxx] = React.useState(initValue)  
(3). useState()说明:
        参数: 第一次初始化指定的值在内部作缓存
        返回值: 包含2个元素的数组, 第1个为内部当前状态值, 第2个为更新状态值的函数
(4). setXxx()2种写法:
        setXxx(newValue): 参数为非函数值, 直接指定新的状态值, 内部用其覆盖原来的状态值
        setXxx(value => newValue): 参数为函数, 接收原本的状态值, 返回新的状态值, 内部用其覆盖原来的状态值

//app.js
import React, { Component } from 'react'
import './App.css'
import SetStateA from './components/Hooks'

export default class App extends Component{
  render(){
    return(
      <div>
		    <SetStateA></SetStateA>
	  </div>
    )
  }
}

//函数式子组件
import React from 'react'
//函数式组件的
function Demo(){
    const [count,setCount] = React.useState(0)
    const [name,setName]=React.useState('张三')
    //console.log(count,setCount)
    function add(){
        console.log("点击事件")
        //setCount(count+1)//第一种写法
        //第二种写法
        setCount((count)=>{
            return count+1
        })
    }
    function changeName(){
        setName("李四")
    }
    return (
        <div>
         <h2>当前求和为{count}</h2>
         <h2>名字是{name}</h2>
         <button onClick={add}>加1</button>
         <button onClick={changeName}>点我改名字</button>
       </div>
    )
}
export default Demo

Ref Hook

(1). Ref Hook可以在函数组件中存储/查找组件内的标签或任意其它数据
(2). 语法: const refContainer = useRef()

//父组件
import React, { Component } from 'react'
import './App.css'
import SetStateA from './components/Hooks'

export default class App extends Component{
  render(){
    return(
      <div>
		    <SetStateA></SetStateA>
	  </div>
    )
  }
}
//子组件
import React from 'react'
//函数式组件的
function Demo(){
    const myRef = React.useRef()
    function show(){
       alert(myRef.current.value)
    }
    return (
        <div>
         <input type="text" ref={myRef} />
         <button onClick={show}>点我提示</button>
       </div>
    )
}
export default Demo

Fragment

可用于取代一个真实的DOM根标签

import React, { Component,Fragment } from 'react'

export default class FragMent extends Component {
  render() {
    return (
      <Fragment>
        <input type="text" />
        <button>点击</button>
      </Fragment>
    )
  }
}

Component

> 1. 只要执行setState(),即使不改变状态数据, 组件也会重新render() ==> 效率低
>
> 2. 只当前组件重新render(), 就会自动重新render子组件，纵使子组件没有用到父组件的任何数据 ==> 效率低

### 效率高的做法

>  只有当组件的state或props数据发生改变时才重新render()

### 原因

>  Component中的shouldComponentUpdate()总是返回true

### 解决

    办法1: 
        重写shouldComponentUpdate()方法
        比较新旧state或props数据, 如果有变化才返回true, 如果没有返回false
    办法2:  
        使用PureComponent
        PureComponent重写了shouldComponentUpdate(), 只有state或props数据有变化才返回true
        注意: 
            只是进行state和props数据的浅比较, 如果只是数据对象内部数据变了, 返回false  
            不要直接修改state数据, 而是要产生新数据
    项目中一般使用PureComponent来优化

 render props（向组件内部动态传入带内容的结构）

Vue中: 
        使用slot技术, 也就是通过组件标签体传入结构  <A><B/></A>
    React中:
        使用children props: 通过组件标签体传入结构
        使用render props: 通过组件标签属性传入结构,而且可以携带数据，一般用render函数属性

### children props

    <A>
      <B>xxxx</B>
    </A>
    {this.props.children}
    问题: 如果B组件需要A组件内的数据, ==> 做不到 

### render props

    <A render={(data) => <C data={data}></C>}></A>
    A组件: {this.props.render(内部state数据)}
    C组件: 读取A组件传入的数据显示 {this.props.data} 

//父组件
import React, { Component } from 'react'
import './App.css'
import SetStateA from './components/RenderProps'

export default class App extends Component{
  render(){
    return(
      <div>
		    <SetStateA></SetStateA>
	  </div>
    )
  }
}

//子组件  父组件中包含子组件的子组件，并实现传递数据
import React, { Component } from 'react'
import './index.css'

export default class Parent extends Component {
  render() {
    return (
      <div className='parent'>
        <h3>我是props样式</h3>
        <h4>这是父组件里面又包含了一个子组件</h4>
        <A render={(name)=><B name={name}/>}/>
      </div>
    )
  }
}

class A extends Component{
    state={name:"张三"}
    render(){
        const {name} = this.state
        return(
            <div className='a'>
                <h3>我是A组件</h3>
                <h4>{this.props.render(name)}</h4>
            </div>
        )
    }
}

class B extends Component{
    render(){
        return(
            <div className='b'>
                <h3>我是B组件{this.props.name}</h3>
            </div>
        )
    }
} 

错误边界

1,错误边界(Error boundary)：用来捕获后代组件错误，渲染出备用页面

2,只能捕获后代组件生命周期产生的错误，不能捕获自己组件产生的错误和其他组件在合成事件、定时器中产生的错误

3,使用方式getDerivedStateFromError

//父组件
import React, { Component } from 'react'
import './App.css'
import SetStateA from './components/ErrorDer'

export default class App extends Component{
  render(){
    return(
      <div>
		    <SetStateA></SetStateA>
	  </div>
    )
  }
}


//子组件里面包含子组件
import React, { Component } from 'react'
import Child from './child'

export default class index extends Component {
  //用于标识子组件是否产生错误
  state={
    hasError:""
  }
  static getDerivedStateFromError(error){
    console.log("@@@",error)
    return {hasError:error}
  }
  //用于子组件会出现的问题，在父组件提交做预判
  render() {
    return (
      <div>
        {this.state.hasError?<h2>请稍后在试吧</h2>:<Child></Child>}
      </div>
    )
  }
}
//child组件
import React, { Component } from 'react'

export default class index extends Component {
  //对应的子组件里面出现的错误
  state={
    // users:[
    //     {id:"01",name:"张三"},
    //     {id:"02",name:"李四"},
    //     {id:"03",name:"王五"}
    // ]
    users:'张三'
  }
  //只能处理生命周期里面处理的错误  一般用于处理render里面出现的错误
  render() {
    return (
      <div>
        <h2>我是子组件</h2>
        {
            this.state.users.map((userObj)=>{
                return <h3 key={userObj.id}>{userObj.name}</h3>
            })
        }
      </div>
    )
  }
}

组件通信方式总结

1,组件间的关系：

- 父子组件
- 兄弟组件（非嵌套组件）
- 祖孙组件（跨级组件）

2,几种通信方式：

        1.props：
            (1).children props
            (2).render props
        2.消息订阅-发布：
            pubs-sub
        3.集中式管理：
            redux
        4.conText:
            生产者-消费者模式

3, 比较好的搭配方式：
        父子组件：props
        兄弟组件：消息订阅-发布、集中式管理
        祖孙组件(跨级组件)：消息订阅-发布、集中式管理、conText(开发用的少，封装插件用的多)