一旦更新了父组件的状态，组件就不会更新

// 父组件
class ParentComponent extends React.Component {
  state = { count: 0 };

  handleClick = () => {
    this.setState({ count: this.state.count + 1 });
  };

  render() {
    return (
      <div>
        <ChildComponent count={this.state.count} />
        <button onClick={this.handleClick}>Increment</button>
      </div>
    );
  }
}

// 子组件
function ChildComponent({ count }) {
  return <div>{count}</div>;
}

class ChildComponent extends React.Component {
  shouldComponentUpdate(nextProps, nextState) {
    return nextProps.count !== this.props.count;
  }

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

const ChildComponent = React.memo(({ count }) => {
  return <div>{count}</div>;
}, (prevProps, nextProps) => prevProps.count === nextProps.count);

class ParentComponent extends React.Component {
  state = { count: 0 };

  handleClick = () => {
    this.setState({ count: this.state.count + 1 });
  };

  render() {
    return (
      <div>
        <ChildComponent count={this.state.count} />
        <button onClick={this.handleClick}>Increment</button>
      </div>
    );
  }
}