组件通讯 event bus事件总线 ,Context和prop

一、event bus 事件总线 进行非父子组件间的通信（兄弟组件）

yarn add -D events
Main.js-==》Header.js
APP.js------------------------------------------------------------------------------
import React, { Component } from 'react';
import Header from './Header';
import Main from './Main';

export default class App extends Component {
  render() {
    return (
      <div>
        {/* 兄弟组件 */}
        <Header />
        <Main />
      </div>
    );
  }
}
Main.js组件------------------------------------------------------------------------------
import React, { Component } from 'react'
import eventBus from './event'

export default class Main extends Component {
    render() {
        return (
            <div>
                <h2>Main组件</h2>
                <button onClick={e => this.emitter()}>发送事件</button>
            </div>
        )
    }
    emitter() {
        const obj = {
            name: '芳芳老师',
            age: 19
        }
        const n = 123;
        //发送sayHello事件，并且传递obj,n
        eventBus.emit('sayHello', obj, n);
    }
}
Header.js组件------------------------------------------------------------------------------
import React, { Component } from 'react'
import eventBus from './event'

export default class Header extends Component {
    //监听sayHello事件
    componentDidMount() {
        eventBus.addListener('sayHello', this.handleSayHello);
    }
    //处理事件监听
    handleSayHello(obj, n) {
        console.log(obj, n);
    }
    //移除事件监听
    componentWillUnmount() {
        eventBus.removeListener('sayHello', this.handleSayHello);
    }
    render() {
        return (
            <div>
                <h1>Header组件</h1>
            </div>
        )
    }
}

二、Context的应用场景：在于很多不同层级的组件需要访问同样一些的数据，谨慎使用，因为这样会使得组件的复用性变差
祖先==》所有后代

import React, { Component } from 'react'

const obj = {
  name: '方方',
  age: 18
}
//为Father组件创建context()对象，传入一个默认值
const FatherContext = React.createContext(obj);

class Child extends Component {
  // context对象赋值给contextType属性 
  //可以通过this.context去使用context的值
  static contextType = FatherContext;
  render() {
    console.log(this.context);
    return (
      <div>
        我是儿子组件，接到的值为：
        <h3>{this.context.name}</h3>
        <h3>{this.context.age}</h3>
      </div>
    )
  }
}

//函数式类
function Father() {
  return (
    <FatherContext.Consumer>
      {
        value => (
          <div>我是父亲组件接到的值为：
            <h3>{value.name}</h3>
            <h3>{value.age}</h3>
            <Child />
          </div>
        )
      }
    </FatherContext.Consumer>
  )
}

export default class App extends Component {
  constructor() {
    super();
    this.state = {
      name: '星星星星',
      age: 24
    }
  }
  //用Provide将当前的state传递给下级组件
  render = () => (
    <div>
      我是爷爷组件
        <FatherContext.Provider value={this.state}>
        <Father />
      </FatherContext.Provider>
    </div >
  )
}

三、props父子组件通信
props一层一层的传

import React, { Component } from 'react';

// 父组件
export default class App extends Component {
  render() {
    return (
      <div>
        {/* 通过一个props去传递，传递一个属性，它的值是一个方法 */}
        <Profile money='父传子' customize={(str) => { this.CustomEvent(str); }} />
      </div>
    );
  }

  // CustomEvent
  CustomEvent(str) {
    console.log(str);
  }
}
// 子组件
class Profile extends Component {
  constructor(props) {
    console.log(props);
    super(props);
    this.state = {
      name: '芳芳老师',
    };
  }
  render() {
    return (
      <div>
        <h2>profile</h2>
        <button onClick={(e) => { this.getString(this.state.name); }}>点击</button>
      </div>
    );
  }
  getString(str) {
    const { customize } = this.props;
    customize(str);
  }
}