无法在React中设置变量中的值

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      myVariable: 'initial value'
    };
  }

  updateVariable() {
    this.setState({ myVariable: 'new value' });
  }

  render() {
    return (
      <div>
        <p>{this.state.myVariable}</p>
        <button onClick={() => this.updateVariable()}>Update Variable</button>
      </div>
    );
  }
}

class ParentComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      myVariable: 'initial value'
    };
  }

  updateVariable() {
    this.setState({ myVariable: 'new value' });
  }

  render() {
    return (
      <div>
        <ChildComponent myVariable={this.state.myVariable} />
        <button onClick={() => this.updateVariable()}>Update Variable</button>
      </div>
    );
  }
}

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