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Detailed explanation of component rendering in React

php中世界最好的语言Original: 2018-05-24 14:38:231722browse

This time I will bring you a detailed explanation of the use of component rendering in React. What are the precautions when using component rendering in React. Here are practical cases, let’s take a look.

Component rendering - conditional rendering (dynamic component)

In many cases the component is dynamically rendered, such as login status. If logged in, log out will be displayed, otherwise login will be displayed

import React from 'react'
let Login = (props) => {
    return <input type="button" value="login" onClick={props.click}/>;
}
let Logout = (props) => {
    return <input type="button" value="logout" onClick={props.click}/>;
}
export default class CP extends React.Component{
    state = {
        status: 0
    }
    login(){
        this.setState({status: 1})
    }
    logout(){
        this.setState({status: 0})
    }
    render(){
        let button = null;
        if(this.state.status == 0){
            button = <Login click={this.login.bind(this)}/>
        } else {
            button = <Logout click={this.logout.bind(this)} />
        }
        return <p>{button}</p>
    }
}

Effect preview

Component rendering - list rendering

React has no instructions, so you have to use an array to complete the list rendering.

List rendering——Simple implementation

import React from 'react'
import ReactDOM from 'react-dom'
let Component1 = () => {
    let lis = [<li key="Javascript">Javascript</li>, <li key="Vue">Vue</li>, <li key="React">React</li>]
    return (
        <p>
            <ul>
                {lis}
            </ul>
        </p>
    )
}
ReactDOM.render(
    <Component1 />
    document.getElementById('app')
)

List rendering——Loop for

import React from 'react'
import ReactDOM from 'react-dom'
let Component1 = () => {
    let data = ['Javascript', 'Vue', 'React']
    let lis = [];
    for(let frm of frms){
        lis.push(<li key={frm}>{frm}</li>)
    }
    return (
        <p>
            <ul>
                {lis}
            </ul>
        </p>
    )
}
ReactDOM.render(
    <Component1 />
    document.getElementById('app')
)

List rendering——Loop map

import React from 'react'
import ReactDOM from 'react-dom'
let Component1 = () => {
    let data = ['Javascript', 'Vue', 'React']
    let lis = data.map((frm) => {
        return <li key={frm}>{frm}</li>
    });
    return (
        <p>
            <ul>
                {lis}
            </ul>
        </p>
    )
}
ReactDOM.render(
    <Component1 />
    document.getElementById('app')
)

List rendering——Object Array

import React from 'react'
import ReactDOM from 'react-dom'
class Component1 extends React.Component {
    constructor(props){
        super(props)
    }
    static defaultProps = {
        students: [
            {id: 1, name: 'Tom', age: 18, gender: 1}, 
            {id: 2, name: 'Sam', age: 22, gender: 1}, 
            {id: 3, name: 'Lucy', age: 20, gender: 0}
        ]
    }
    getKeys(item = {}){
        return Object.keys(item)
    }
    render(){
        return (
            <table>
                <thead>
                    <tr>
                        {
                            this.getKeys(this.props.students[0]).map((key) => {
                                return <th key={key}>{key}</th>
                            })
                        }
                    </tr>
                </thead>
                <tbody>
                    {
                        this.props.students.map((obj) => {
                            return (
                                <tr key={obj.id}>
                                    {
                                        this.getKeys(obj).map((key, idx) => {
                                            return <td key={key + idx}>{obj[key]}</td>
                                        })
                                    }
                                </tr>
                            )
                        })
                    }
                </tbody>
            </table>
        )
    }
}
ReactDOM.render(
    <Component1 />,
    document.getElementById('app')
)

List rendering - Keys

Because React is a process from virtual DOM to real DOM, and DOM itself is an object, the object does not have a unique identifier by default, so it needs to be done manually specified.

Keys help React identify which item has been modified, added, or removed. Each element in the array should be identified by a unique and immutable key.

Keys are used in list rendering and must be unique among sibling elements.

Component rendering - component child nodes

Because the component is called as a DOM node, the component can contain child nodes. React obtains the child nodes of the component through this.props.children. Usually this.props.children will have the following situations

If the current component has no child nodes, it is undefined
If there is a child node, The data type is object
If there are multiple child nodes, the data type is array

In order to solve the problem of inconsistent data types that require constant judgment during use, React provides a method Reactth.Children to handle this property.

var Component1 = React.createClass({
    render: function(){
        return (
            <p>                        
                {
                    React.Children.map(this.props.children, function(childNode){
                        return <li>{childNode}</li>
                    })
                }
            </p>
        );
    }
})
ReactDOM.render(
    <Component1>
        <span>Tom</span>
        <span>Sam</span>
    </Component1>, document.getElementById('p1'));

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!