Subscription Holder Lifecycle

subscription_holder Lifecycle Management Guide

subscription_holder eliminates manual tracking and disposal of multiple StreamSubscription instances. It acts as a disposable container (similar to Rx CompositeDisposable) that cancels all active subscriptions cleanly when tearing down state.

Guidelines

• Using SubscriptionHolder:
  • Instantiate final _subscriptions = SubscriptionHolder();.
  • Add active subscriptions via _subscriptions.add(stream.listen(...)) or use the fluent extension .addTo(_subscriptions).
  • Call _subscriptions.dispose() inside State.dispose(), ChangeNotifier.dispose(), or controller teardown.
• Using SubscriptionHolderMixin:
  • Mix in SubscriptionHolderMixin directly onto state classes or controller classes to access addSubscription(stream.listen(...)) and automatic disposal.
• Auto-Cancellation:
  • dispose() cancels all registered subscriptions and prevents subsequent additions.
  • To cancel existing subscriptions without invalidating the container (e.g., when resetting state), call _subscriptions.cancelAll().

Examples

1. Managing Subscriptions in a StatefulWidget

import 'dart:async';
import 'package:flutter/material.dart';
import 'package:subscription_holder/subscription_holder.dart';

class EventMonitorWidget extends StatefulWidget {
  const EventMonitorWidget({super.key, required this.eventStream, required this.errorStream});

  final Stream<String> eventStream;
  final Stream<dynamic> errorStream;

  @override
  State<EventMonitorWidget> createState() => _EventMonitorWidgetState();
}

class _EventMonitorWidgetState extends State<EventMonitorWidget> {
  final _subscriptions = SubscriptionHolder();

  @override
  void initState() {
    super.initState();

    // Using .addTo() extension
    widget.eventStream.listen((event) {
      debugPrint('Received: $event');
    }).addTo(_subscriptions);

    // Using .add() directly
    _subscriptions.add(widget.errorStream.listen((err) {
      debugPrint('Error: $err');
    }));
  }

  @override
  void dispose() {
    _subscriptions.dispose(); // Cancels both subscriptions immediately
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return const SizedBox.shrink();
  }
}

2. Using SubscriptionHolderMixin in StateNotifier / ChangeNotifier

import 'package:flutter/foundation.dart';
import 'package:subscription_holder/subscription_holder.dart';

class SessionController extends ChangeNotifier with SubscriptionHolderMixin {
  SessionController(Stream<bool> authStateStream, Stream<int> tickStream) {
    authStateStream.listen((isAuthenticated) {
      // Handle auth update
      notifyListeners();
    }).addTo(subscriptionHolder);

    tickStream.listen((tick) {
      // Handle timer tick
    }).addTo(subscriptionHolder);
  }

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

Common Pitfalls & Anti-Patterns

• ❌ Anti-pattern: Manually maintaining individual nullable StreamSubscription? _sub1; StreamSubscription? _sub2; variables and cancelling each in dispose(), which is error-prone and easily leads to memory leaks.
  • ✔️ Correct: Collect all subscriptions into SubscriptionHolder and dispose them together.
• ❌ Anti-pattern: Calling add() on a SubscriptionHolder that has already been disposed.
  • ✔️ Correct: Only register subscriptions during the active lifecycle of the component.