flutter-sport/lib/services/app_subscription_state.dart

import 'dart:async';

import 'package:flutter/material.dart';

mixin SubscriptionState<T extends StatefulWidget> on State<T> {
  final List<StreamSubscription<dynamic>> _streamSubscriptions = <StreamSubscription<dynamic>>[];

  void addSubscription(StreamSubscription<dynamic> streamSubscription) {
    _streamSubscriptions.add(streamSubscription);
  }

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

  disposeSubscription() async {
    for (StreamSubscription<dynamic> subscription in _streamSubscriptions.reversed) {
      await subscription.cancel();
    }
    _streamSubscriptions.clear();
  }
}