React组件传值（类组件）

父组件给子组件传值

父组件：使用子组件时，直接传入值(attr=value)
子组件：类组件通过this.props.attr获取父组件传来的值，函数组件通过props.attr获取父组件传来的值

//父组件
import React from "react";
import Message from '../Message/messageIndex'

export default class City extends React.Component{
    constructor(){
        super()
        this.state={
            name:'父组件'
        }
    }
    render(){
        return (
            <div>
                <Message name={this.state.name}></Message>
            </div>   
        )
    }
}

//子组件
import React from "react";

export default class Message extends React.Component{
    constructor(props){
        super(props)
        this.state={
            info:'子组件'
        }
    }
    render(){
        return (
            <div>{this.props.name}</div>
        )
    }
}

子组件给父组件传值

父组件：给子组件传一个函数，通过子组件调用并传入参数，获取子组件的值，将值保存至state中
子组件：通过this.props（函数组件通过props）获取整个函数，然后在参数中传入待传递的值

//父组件
import React from "react";
import Message from '../Message/messageIndex'

export default class City extends React.Component{
    constructor(){
        super()
        this.state={
            name:'父组件',
            message:''
        }
    }
    getMessage=(msg)=>{
        this.setState({
            message:msg
        })
    }
    render(){
        return (
            <div>
                {/* <Message name={this.state.name} getInfo={this.getMessage}></Message> */}
                <Message getInfo={this.getMessage}></Message>
                <h4>子组件传来的值：{this.state.message}</h4>
            </div>
            
        )
    }
}

//子组件
import React from "react";

export default class Message extends React.Component{
    constructor(props){
        super(props)
        this.state={
            info:'我是子组件'
        }
        this.props.getInfo(this.state.info)
    }
    render(){
        return (
            // <div>{this.props.name}</div>
            <div></div>
        )
    }
}

兄弟组件传值

子组件A===》父组件===》子组件B
同上

祖孙组件传值

在单独的js文件中创建context
在需要传值与接收值的祖孙组件中引入创建的context

//context.js
import React from "react";
export const ThemeContext = React.createContext('none');
export default function(){}

//爷爷
import React from "react";
import Message from '../Message/messageIndex'
import {ThemeContext} from '../../Context/context'

class City extends React.Component{
    constructor(){
        super()
        this.state={
            name:'父组件',
            message:'',
            sonson:'wuwuwu'
        }
    }
    // getMessage=(msg)=>{
    //     this.setState({
    //         message:msg
    //     })
    // }
    render(){
        return (
            <div>
                <ThemeContext.Provider value={this.state.sonson}>
                    <Message></Message>
                </ThemeContext.Provider>
            </div>
            
        )
    }
}
City.contextType = ThemeContext
export default City

//孙子
import React from "react"
import {ThemeContext} from '../../Context/context'

class MyButton extends React.Component {
    constructor(props){
        super(props)
    }
    
    render() {
        return <div style={
    
    {color:'red'}}>{this.context}</div>
    }
  }
MyButton.contextType=ThemeContext
export default MyButton