例如，您可以这样做：

import 'package:flutter/material.dart';

void main() {
  runApp(const MaterialApp(home: B()));
}

class B extends StatefulWidget {
  const B({super.key});

  @override
  State<B> createState() => BState();
}

class BState extends State<B> {
  @override
  Widget build(BuildContext context) {
    print('B updates');
    return Scaffold(
        body: Column(
      children: [A(updater: update)],
    ));
  }

  void update() {
    setState(() {

    });
  }
}

class A extends StatefulWidget {
  final Function? updater;

  const A({Key? key, this.updater}) : super(key: key);

  @override
  State<A> createState() => _AState();
}

class _AState extends State<A> {

  @override
  void setState(VoidCallback fn) {
    if (widget.updater != null) widget.updater!();
    super.setState(fn);
  }

  @override
  Widget build(BuildContext context) {
    return TextButton(
        onPressed: () {
          setState(() {
            print('clicked button');
          });
        },
        child: const Text('click'));
  }
}

每当点击按钮时，它会将两个“点击的按钮”打印为“B更新”。因此，每次点击时B都会重建。如果您在A中忽略setState覆盖，您将只会看到“点击的按钮”打印。