为什么当构造器参数改变时，StatefulWidget的子状态不会被重置？

class MyWidget extends StatefulWidget {
  final int param;

  MyWidget({required this.param, Key? key}) : super(key: key);

  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  int _state = 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('StatefulWidget Example')),
      body: Center(
        child: Text('State: $_state'),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          setState(() {
            _state++;
          });
        },
        child: Icon(Icons.add),
      ),
    );
  }
}

MyWidget(key: ValueKey(widget.param), param: newValue);

class _MyWidgetState extends State<MyWidget> {
  int _state = 0;

  @override
  void didUpdateWidget(covariant MyWidget oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (oldWidget.param != widget.param) {
      setState(() {
        _state = 0; // 重置状态
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    // 构建逻辑
  }
}