React操作DOM之forwardRef问题

import React, { PureComponent,createRef,forwardRef } from 'react'

const Profile = forwardRef(function (props,ref){
  return <h2 ref={ref}>Profile</h2>
})

export default class App extends PureComponent {
  constructor(props){
    super(props);
    this.profileRef = createRef()
  }
  render() {
    return (
      <div>
        <Profile ref={this.profileRef} name={'lsh'}/>
        <button onClick={e=>this.printRef()}>点击</button>
      </div>
    )
  }
  printRef(){
    console.log(this.profileRef.current)
  }
}

import React, { useRef } from 'react';
import Content from './content';

const Home = () => {
  // 创建一个Ref对象
  const connectRef = useRef(null);

  const handleFoucus = () => {
    const _ref = connectRef.current;
    _ref.focus();
  };

  return (
    <div>
        <button onClick={() => handleFoucus()}>
          使用子组件中DOM元素的方法
        </button>

        <Content ref={connectRef} />
    </div>
  );
};

export default Home;

import React, { forwardRef } from 'react';

/**
 * forwardRef包裹后，ref会作为第二个参数，接收传进来的ref属性
 * e.g.
 * <Content count={count} user={user} ref={connectRef}>
 *
 * @param props - {count, user}
 * @param ref   - connectRef
 * */
const Content = (props, ref) => {
  return (
    <div>
   	  {/* 把ref绑定给传进来的ref ≈ ref={connectRef} */}
      <input type="password" ref={ref} />
    </div>
  )
};

export default forwardRef(Content);

import React, { useRef } from 'react';
import Content from './content';

const Home = () => {
  // 创建一个Ref对象
  const connectRef = useRef(null);

  const handleAdd = () => {
    const _ref = connectRef.current;

    const { count } = _ref.state;
    _ref.setState({
      count: count + 1
    })
  };

  return (
    <div>
        <button onClick={() => handleAdd()}>
          使用子组件中class组件的属性和方法
        </button>

        <Content ref={connectRef} />
    </div>
  );
};

export default Home;

import React, { forwardRef } from 'react';
import Header from './header';
import Footer from './footer';

/**
 * forwardRef包裹后，ref会作为第二个参数，接收传进来的ref属性
 * e.g.
 * <Content count={count} user={user} ref={connectRef}>
 *
 * @param props - {count, user}
 * @param ref   - connectRef
 * */
const Content = (props, ref) => {
  return (
    <div>
      {/* 把ref绑定给传进来的ref ≈ ref={connectRef} */}
      <Header ref={ref} />  {/* class组件 */}
		
      {/* <Footer ref={ref} /> 函数组件是没有实例的，所以connectRef.current: null */}
    </div>
  )
};

export default forwardRef(Content)

import React from 'react';

export default class Header extends React.Component {
  state = {
    count: 0
  };

  render() {
    return (
      <div>
        {this.state.count}
      </div>
    )
  }
};

/*
  处理ref
  e.g. Hoc1(Hoc2(Content))

  <Content ref={myRef} /> 给Content绑定的ref会绑定到Hoc1上，且不会继续向下传递

  第一种方法 React.forwardRef ===============

      在 Hoc1外面 用React.forwardRef()对ref做处理，用props来传递ref
      0. 在高阶组件外面包裹forwardRef，拦截获取ref，增加一个props（xxx={ref}），真实组件通过props.xxx获取
      1. 使用时传 ref={XXXX}  // 和第二种方法不同的地方
      2. 用forwardRef的第二个参数获取 ref
      3. 增加一个新的props，用来向下转发ref  e.g. forwardedRef={ref}
      4. 真实组件中绑定 ref={props.forwardedRef}

      const Home = (props) => {
        const connectRef = useRef(null);

        return (
          <div>
            <Content ref={connectRef} />
          </div>
        );
      };

      // 被包装组件
      const Content = (props) => {
        return (
          <div>
            <input type="password" ref={props.forwardedRef} />
          </div>
        );
      };


      // forwardRef的第二个入参可以接收ref，在Hoc外层对ref做处理
      export default React.forwardRef((props, ref) => {
        const Wrapper = withRouter(Content);  // Hoc

        // forwardRef包裹的是Wrapper
        // 需要在Wrapper中把ref向下传递给真实组件
        // Wrapper中增加一个props属性，把ref对象作为props传给子组件
        return <Wrapper {...props} forwardedRef={ref} />;
      });

  第二种方法 ==========

  0. 使用时就用一个props来保存ref
  1. 使用时传 xxx={ref}  // 和第一种方法的不同点
  2. 真实组件中绑定 ref={props.xxx}

  const Home = (props) => {
    const connectRef = useRef(null);

    return (
      <div>
        <Content forwardedRef={connectRef} />
      </div>
    );
  };

  // 定义高阶组件
  export const Hoc = (WrappedComponent) => {
    class Wrapper extends React.Component {
      render() {
        return <WrappedComponent {...props} />
      }
    }
  }

  // 被包装的组件
  const Content = (props) => {
    return (
      <div>
        <input type="password" ref={props.forwardedRef} />
      </div>
    );
  };

  // 包装过程
  export default Hoc(Content);

* */