React未更改父元素的状态

// 父组件
class ParentComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0
    };
  }

  updateCount = (newCount) => {
    this.setState({ count: newCount });
  }

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

// 子组件
class ChildComponent extends React.Component {
  handleClick = () => {
    const newCount = this.props.count + 1;
    this.props.updateCount(newCount);
  }

  render() {
    return (
      <div>
        <button onClick={this.handleClick}>增加计数</button>
      </div>
    );
  }
}