React组件应在获取新数据之前装入以前的状态

import React, { Component } from 'react';

class MyComponent extends Component {
  constructor(props) {
    super(props);
    this.state = {
      loading: true,
      data: null
    };
  }

  componentDidMount() {
    this.fetchData();
  }

  componentDidUpdate(prevProps) {
    if (prevProps.someProp !== this.props.someProp) {
      this.fetchData();
    }
  }

  fetchData() {
    this.setState({ loading: true });

    // 调用API获取新数据
    // ...

    // 数据加载完成后更新状态
    this.setState({
      loading: false,
      data: newData
    });
  }

  render() {
    const { loading, data } = this.state;

    if (loading) {
      return <div>Loading...</div>;
    }

    return (
      <div>
        {/* 使用获取的数据进行渲染 */}
      </div>
    );
  }
}

export default MyComponent;