访问子组件中在父组件中定义的变量

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

class ParentComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      parentVariable: 'Hello from parent',
    };
  }

  render() {
    return (
      <div>
        <ChildComponent variableFromParent={this.state.parentVariable} />
      </div>
    );
  }
}

export default ParentComponent;

import React from 'react';

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

export default ChildComponent;