BadFL Example Code (impl/event_center)

main.dart

import 'package:flutter/material.dart';

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

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

  void handler1(dynamic eventData) {
    print('in handler1: $eventData');
  }

  void handler2(dynamic eventData) {
    print('in handler2: $eventData');
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: ListView(
          children: [
            ElevatedButton(
              onPressed: () => BadEventCenter.listen('ev1', handler1),
              child: const Text('add handler1'),
            ),
            ElevatedButton(
              onPressed: () => BadEventCenter.listen('ev1', handler2),
              child: const Text('add handler2'),
            ),
            ElevatedButton(
              onPressed: () => BadEventCenter.unListen('ev1', handler2),
              child: const Text('remove handler2'),
            ),
            ElevatedButton(
              onPressed: () => BadEventCenter.unListen('ev1', handler1),
              child: const Text('remove handler1'),
            ),
            ElevatedButton(
              onPressed: () => BadEventCenter.unListen('ev1'),
              child: const Text('remove all handler on ev1'),
            ),
            ElevatedButton(
              onPressed: () => BadEventCenter.unListenAll(),
              child: const Text('remove all handler'),
            ),
            ElevatedButton(
              onPressed: () => BadEventCenter.trigger('ev1', 'data'),
              child: const Text('trigger ev1'),
            ),
          ],
        ),
      ),
    );
  }
}

typedef EventHandler = void Function(dynamic eventData);

typedef StopListen = void Function();

/// `impl::event_center`: event center implementation
abstract class BadEventCenter {
  static final Map<String, Set<EventHandler>> _handlers = {};

  /// add a [handler] on [eventName]
  static StopListen listen(String eventName, EventHandler handler) {
    var handlers = _handlers[eventName];
    if (handlers == null) {
      _handlers[eventName] = {handler};
    } else {
      handlers.add(handler);
    }

    return () {
      handlers?.remove(handler);
    };
  }

  /// remove specific [handler] on [eventName],
  /// if [handler] is null, remove all handlers on [eventName]
  static void unListen(String eventName, [EventHandler? handler]) {
    if (handler == null) {
      _handlers.remove(eventName);
    } else {
      _handlers[eventName]?.remove(handler);
    }
  }

  /// remove all handlers on all events
  static void unListenAll() {
    _handlers.clear();
  }

  /// trigger all handlers on [eventName] with [eventData]
  static void trigger(String evName, [dynamic eventData]) {
    var handlers = _handlers[evName];
    if (handlers == null) {
      return;
    }

    for (var handler in handlers) {
      handler(eventData);
    }
  }
}