为什么代码触发了“太多的渲染”，为什么它是“未定义的”？

import React, { useState } from 'react';

function MyComponent() {
  const [count, setCount] = useState(0);

  // 错误的做法：直接调用状态更新函数
  setCount(count + 1);

  return (
    <div>
      <p>Count: {count}</p>
    </div>
  );
}

export default MyComponent;

import React, { useState, useEffect } from 'react';

function MyComponent() {
  const [count, setCount] = useState(0);

  // 使用事件处理程序
  const handleClick = () => {
    setCount(count + 1);
  };

  // 使用useEffect钩子
  useEffect(() => {
    console.log('Component has mounted or updated');
  }, [count]);

  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={handleClick}>Increment</button>
    </div>
  );
}

export default MyComponent;

import React, { useState, useEffect } from 'react';

function MyComponent() {
  const [data, setData] = useState();

  useEffect(() => {
    fetchData();
  }, []);

  const fetchData = async () => {
    const response = await fetch('https://api.example.com/data');
    const result = await response.json();
    setData(result);
  };

  // 错误的做法：在数据加载完成之前访问data
  console.log(data.someProperty);

  return (
    <div>
      {data ? <p>{data.someProperty}</p> : <p>Loading...</p>}
    </div>
  );
}

export default MyComponent;

import React, { useState, useEffect } from 'react';

function MyComponent() {
  const [data, setData] = useState(null);

  useEffect(() => {
    fetchData();
  }, []);

  const fetchData = async () => {
    const response = await fetch('https://api.example.com/data');
    const result = await response.json();
    setData(result);
  };

  // 正确的做法：在数据加载完成之后访问data
  if (data) {
    console.log(data.someProperty);
  }

  return (
    <div>
      {data ? <p>{data.someProperty}</p> : <p>Loading...</p>}
    </div>
  );
}

export default MyComponent;