你的代码中的问题是你在onPressed方法的回调中使用了私有bool变量，这导致了问题。
下面是工作代码：

class Entry extends StatefulWidget {
  const Entry({Key? key}) : super(key: key);

  @override
  State<Entry> createState() => _EntryState();
}

class _EntryState extends State<Entry> {
  bool _isExpanded = true;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Center(
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Container(
            color: const Color(0xffeaeaea),
            child: Row(
                mainAxisAlignment: MainAxisAlignment.spaceBetween,
                children: [
                  Container(
                    child: Text('Description'),
                  ),
                  ExpandIcon(
                    isExpanded: _isExpanded,
                    color: Colors.white,
                    expandedColor: Colors.black,
                    disabledColor: Colors.grey,
                    onPressed: (bool isExpanded) {
                      setState(() {
                        _isExpanded = !isExpanded;
                      });
                    },
                  ),
                ]),
          ),
          if (_isExpanded) const Text('Data'),
        ],
      ),
    ));
  }
}

在MyScreen类内部但在_MyScreenState类外部声明_isExpanded布尔变量，可以使其成为MyScreen类的成员变量。它允许您从build（）方法和ExpandIcon小部件的onPressed回调访问该变量。

请尝试此代码：

class MyScreen extends StatefulWidget {
  @override
  State<MyScreen> createState() => _MyScreenState();
}
bool _isExpanded = true;

class _MyScreenState extends State<MyScreen> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('My Screen'),
        backgroundColor: Colors.blueGrey[900], // set the background color here
      ),
      body: Center(
        child: Column(
          children: [
            Container(
      color: const Color(0xffeaeaea),
      child: Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: [
                Container(
                  child: Text('Description'),
                ),
                ExpandIcon(
                    expandedColor: Colors.black,
                    color: Colors.black,
                    isExpanded: _isExpanded,
                    onPressed: (bool _expended) {
                      setState(() {
                        _isExpanded = !_isExpanded;
                      });
                    }),
              ]),
    ),
        if (_isExpanded) const Text('Data'),
    ]
        ),
      ),
    );
  }
}

• 希望它能解决你的问题！*