flutter事件总线问题,无法将消息从发送方发送到接收方

当使用EventBus函数时,此代码无法在两个不同的类之间发送信息。

import 'package:flutter/material.dart';
import 'package:scoped_model/scoped_model.dart';
import 'package:event_bus/event_bus.dart';
import 'dart:async';

//EventBus usage
final EventBus eventBus = EventBus();

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {

  static final GlobalKey<NavigatorState> navigatorKey =
      GlobalKey<NavigatorState>();
  static var isLoggedIn = false;
 
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    
    return MaterialApp(
      navigatorKey: navigatorKey,
      onGenerateRoute: _generateRoute,

      home: const HomeScreen(),
    );
  }

  Route<dynamic>? _generateRoute(RouteSettings settings) {
    switch (settings.name) {
      case '/':
        return MaterialPageRoute( settings: settings, builder: (context) => const HomeScreen()); //settings的作用是debug, 追溯目前navigator stack中访问过的页面

      case '/transactions':
        return MaterialPageRoute(
          settings: settings, builder: (context) =>  TransactionScreen());
      case '/cart':
        return MaterialPageRoute(
          settings: settings, builder: (context) =>  CartScreen());

      default:
        return null;
    }
  }
}



class HomeScreen extends StatelessWidget {
  const HomeScreen({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Home'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
             ElevatedButton(
              onPressed: () {
                Navigator.of(context).pushNamed('/transactions');
              },
              child: const Text('View transactions'),
            ),
            ElevatedButton(
              onPressed: () {
                Navigator.of(context).pushNamed('/cart');
              },
              child: const Text('View Cart'),
            ),
          ],
        ),
      ),
    );
  }
}


class TransactionScreen extends StatelessWidget {
  String message = 'Justin YC';


  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Transactions'),
      ),
      body: Center(
        child: Column(
          children: [
            ElevatedButton(
              
              onPressed: () {
                Navigator.of(context).pushNamed('/cart');
              },
              child: const Text('View Cart'),
            ),
            ElevatedButton(
              onPressed: () {
                print("event has been sent: $message");
                eventBus.fire(CustomEvent(message));
              },
              child: Text('Tap to send new Info: $message'),
            ),
          ],
        ),
      ),
    );
  }
}

class CustomEvent {
  String msg;
  CustomEvent(this.msg);
}

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

  @override
  State<CartScreen> createState() => _CartScreenState();
}

class _CartScreenState extends State<CartScreen> {
  late StreamSubscription subscription;
  String msg = " 通知：";

  @override
  void initState() {
    
    subscription = eventBus.on<CustomEvent>().listen((event) {
      print('received $event.msg');
      setState(() {msg = event.msg;});
    });
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    

    return Scaffold(
      appBar: AppBar(
        title: const Text('Cart'),
      ),
      body: Center(
        child: Text(msg),
      ),
      
    );
  }

  @override
  void dispose() {
    super.dispose();
  }
}

我尝试了几种不同的方法,包括在启动应用程序时保持两个小部件的活动状态。

我发现,如果我让它们都活着,听众就可以从发送者那里收到消息。然而,这将导致另一个问题,即小部件不再在小部件树上。因此接收器不能进一步处理数据。