如何从子组件中获取值？

import React from 'react';
import ChildComponent from './ChildComponent';

class ParentComponent extends React.Component {
  render() {
    const value = 'Hello World';
    return (
      <div>
        <ChildComponent value={value} />
      </div>
    );
  }
}

export default ParentComponent;

import React from 'react';

class ChildComponent extends React.Component {
  render() {
    const value = this.props.value;
    return (
      <div>
        <p>{value}</p>
      </div>
    );
  }
}

export default ChildComponent;

import React from 'react';

class ChildComponent extends React.Component {
  handleClick = () => {
    const value = 'Hello World';
    this.props.onGetValue(value);
  }

  render() {
    return (
      <div>
        <button onClick={this.handleClick}>Get Value</button>
      </div>
    );
  }
}

export default ChildComponent;

import React from 'react';
import ChildComponent from './ChildComponent';

class ParentComponent extends React.Component {
  handleGetValue = (value) => {
    console.log(value);
  }

  render() {
    return (
      <div>
        <ChildComponent onGetValue={this.handleGetValue} />
      </div>
    );
  }
}

export default ParentComponent;