如何观察Mobx flutter中其他类的字段变量？

import 'package:flutter/material.dart';
import 'package:mobx/mobx.dart';
import 'package:flutter_mobx/flutter_mobx.dart';

// 被观察的类
class Counter extends Observable {
  @observable
  int value = 0;
}

// 观察者类
class CounterObserver extends ObserverWidget {
  final Counter counter;

  CounterObserver({required this.counter});

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Text('Value: ${counter.value}'),
        ElevatedButton(
          onPressed: () {
            counter.value++;
          },
          child: Text('Increment'),
        ),
      ],
    );
  }

  @override
  void afterBuild(BuildContext context) {
    autorun((_) {
      // 在这里可以观察counter的字段变量的变化，并进行相应的处理
      print('Counter value changed: ${counter.value}');
    });
  }
}

void main() {
  final counter = Counter();

  runApp(
    MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Mobx Flutter Example'),
        ),
        body: CounterObserver(counter: counter),
      ),
    ),
  );
}