React :为什么我的组件在由数组状态控制时不能重新呈现？

import React, { Component } from 'react';

class MyComponent extends Component {
  constructor(props) {
    super(props);
    this.state = {
      array: [1, 2, 3]
    };
  }

  addItem = () => {
    const newItem = Math.random();
    this.setState(prevState => {
      const newArray = [...prevState.array];
      newArray.push(newItem);
      return { array: newArray };
    });
  };

  render() {
    return (
      <div>
        <button onClick={this.addItem}>Add Item</button>
        <ul>
          {this.state.array.map((item, index) => (
            <li key={index}>{item}</li>
          ))}
        </ul>
      </div>
    );
  }
}

export default MyComponent;