onConnectivityChanged property

Implementation

@override
Stream<List<String>> get onConnectivityChanged {
  final controller = StreamController<List<String>>.broadcast();
  StreamSubscription<Event>? onlineSub;
  StreamSubscription<Event>? offlineSub;

  void attach() {
    onlineSub ??= EventStreamProvider<Event>(
      'online',
    ).forTarget(window).listen((_) => controller.add(const ['wifi']));
    offlineSub ??= EventStreamProvider<Event>(
      'offline',
    ).forTarget(window).listen((_) => controller.add(const ['none']));
  }

  void detach() {
    onlineSub?.cancel();
    offlineSub?.cancel();
    onlineSub = null;
    offlineSub = null;
  }

  // 首次订阅时挂载浏览器事件监听，最后一次取消时移除，避免反复订阅导致全局
  // 监听累积（泄漏）/ Attach the browser listeners on the first subscription and
  // detach them on the last cancellation so repeated subscriptions don't leak
  // global event listeners.
  controller.onListen = attach;
  controller.onCancel = detach;
  return controller.stream;
}