React系列——HOC高阶组件的封装与使用

技巧一：复用组件逻辑

具体而言，高阶组件是参数为组件，返回值为新组件的函数

const EnhancedComponent = higherOrderComponent(WrappedComponent);

For example:

参数复用

const withSize = (Component) => {
	return class toSize extends Component {
		state = {
			xPos: document.documentElement.clientWidth,
			yPos: document.documentElement.clientHeight
		}

		getPos = () => {
			this.setState({
				xPox: document.documentElement.clientWidth,
				yPos: document.documentElement.clientHeight
			})
		}

		componentDidMount(){
			window.addEventListener('resize', this.getPos)
		}
	
		componentWillUnmount(){
			window.removeEventListener('resize', this.getPos)
		}
		
		render() {
			return <Component {...this.state}/>
		}
	}
}

class Foo extends Component {
	render() {
		return (
			<div>
				<p>x:{ this.props.xPos} -- y: {this.props.yPos} </p>
			</div>
		)
	}
}

class Sub extends Component {
	render() {
		return (
			<div>
				<button>x:{ this.props.xPos} -- y: {this.props.yPos} </button>
			</div>
		)
	}
}

const SubWithSize = withSize(Sub)
const FooWithSize = withSize(Foo)

class App extends Component {
	render() {
		return (
			<div>
				<SubWithSize />
				<FooWithSize />
			</div>	
		)
	}
}

函数逻辑复用

// PhotoList.js
import React from 'react'
import withFetch from '../withFetch'

const url = 'https://www.abc.com/photos?_limit=5

const PhotoList = ({ list }) => {
	return (
		<ul> 
			{list.map((photo) => {
				return <li key={photo.id}> 图片URL：{photo.url}</li>
			})}
		</ul>
	)
}
export default withFetch(PhotoList, url)

// UserList.js
import React from 'react'
import withFetch from '../withFetch'

const url = 'https://www.abc.com/users?_limit=5

const UserList = ({ list }) => {
	return (
		<ul> 
			{list.map((user) => {
				return <li key={user.id}> 用户名：{user.name}</li>
			})}
		</ul>
	)
}
export default withFetch(UserList, url)

import React from 'react'
import axios from 'axios'

const withFetch = (Component, url) => {
	return class WithFetchComponent extends React.Component {
		state = {
			list: []
		}

		async componentDidMount() {
			const { data: list } = await axios.get(url)
			this.setState({
				list
			})
		}

		render() {
			return <Component {...this.props} list={this.state.list} /}
		}
	}
}

技巧二：组件的异步加载

利用lazy、suspense来实现组件的异步加载

• 1、lazy引入异步组件

import ReactDOM from 'react-dom'
import React, { Component, lazy, Suspense } from 'react'
const sub = lazy(() => import('./Sub'))

2、suspense调用组件

class App extends Component {
	render() {
		return (
			<div>
				/*fallback的作用是在异步加载的空档中填充一些内容让页面可以正常渲染 */
				<Suspense fallback = { <div>loading</div> }>
					<Sub />
				</Suspense>
			</div>
		)
	}
}

ReactDOM.render(
	<App />,
	document.getElementById('rroot')
)

技巧三：组件的生命周期

Mounting（挂载）

• constructor(): 在 React 组件挂载之前，会调用它的构造函数。
• getDerivedStateFromProps(): 在调用 render 方法之前调用，并且在初始挂载及后续更新时都会被调用。
• render(): 唯一必须实现的纯函数；
• componentDidMount(): 在组件挂载后（插入 DOM 树中）立即调用。

Updating（更新）

• componentDidUpdate(): 在组件更新后立即调用

Unmounting（卸载）

• componentWillUnmount(): 在组件卸载后理解调用

For example:

class App extends Component {
	constructor(props) {
		super(props)
		this.state = { count: 0 }
		console.log('cons');
	}
	
	onclick = () => {
		this.setState({
			count: this.state.count + 1
		})
	}

	componentDidMount(){
		console.log('did mount');
	}

	componentDidUpdate(){
		console.log('did update');
	}

	componentWillUnmount(){
		console.log('will unmount');
	}

	return() {
		console.log('render')
		return (
			<div>
				<p> {this.state.count} </p>
				<button onclick={this.onclick}>add</button>
			</div>
		)
	}

// 执行顺序:()
// cons -> render -> did mount (mounting阶段)
// -> render -> did update (updating阶段)
// -> will unmount (unmounting阶段)

技巧四：组件的优化

• 避免无数据更新的自组件反复更新
  

import ReactDOM from 'react-dom'
import React, { Component, PureComponent, memo } from 'react'

//组件的优化一: 类组件
class Sub extends Component //方法二：替换成PureComponent {
	// 方法一
	shouldComponentUpdate(nextProps, nextState){
		if (nextProps.name === this.props.name) {
			return false;
		}
		return true;
	}
	render() {
		console.log('sub render');
		return (
			<div>
				sub
			</div>
		)
	}
}

//组件的优化二: 函数组件
const Sub = memo((params) => {
	console.log('sub render');
	return (
		<div>
			sub
		</div>
	)
})

class App extends Component {
	state = {
		count: 0
	}
	
	onclick = () => {
		this.setState({
			count: this.state.count + 1
		})
	}

	callback = () => {
	}
	
	render() {
		return (
			<div>
				<Sub name="zhangsan" />
				// 函数同理
				<Sub func={this.callback} />
				<p> {this.state.count} </p>
				<button onclick={this.onclick}>add</button>
			</div>
		)
	}
}

ReactDOM.render(
	<App />,
	document.getElementById('rroot')
)