解决React hook 'useState' cannot be called in a class component报错_React

// App.js
import {useState, useEffect} from 'react';
class Example {
  render() {
    // ⛔️ React Hook "useState" cannot be called in a class component.
    // React Hooks must be called in a React function component or a custom React Hook function.
    const [count, setCount] = useState(0);
    // ⛔️ React Hook "useEffect" cannot be called in a class component.
    // React Hooks must be called in a React function component or a custom React Hook function.
    useEffect(() => {
      console.log('hello world');
    }, []);
    return (
      <div>
        <button onClick={() => setCount(count + 1)}>Increment</button>
      </div>
    );
  }
}

// App.js
import {useState, useEffect} from 'react';
export default function App() {
  const [count, setCount] = useState(0);
  useEffect(() => {
    console.log('hello world');
  }, []);
  return (
    <div>
      <h2>Count {count}</h2>
      <button onClick={() => setCount(count + 1)}>Increment</button>
    </div>
  );
}

// App.js
import React from 'react';
export default class App extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0,
    };
  }
  render() {
    return (
      <div>
        <h2>Count: {this.state.count}</h2>
        <button onClick={() => this.setState({count: this.state.count + 1})}>
          Increment
        </button>
      </div>
    );
  }
}