broadcast_stream_subscriber

A Dart mixin with a minimal set of methods to add and manage StreamSubscriptions and notify them of events with a broadcast (multi-stream) StreamController.

Usage

import 'package:broadcast_stream_subscriber/broadcast_stream_subscriber.dart';

// Mixin `BoradcastStreamSubscriber` to your class
class ClassName with BroadcastStreamSubscriber<T> {
  ClassName();

  // Dispose of your class
  void dispose() {
    // Cancel any still active `StreamSubscriptions`
    // and close the `StreamController`.
    closeStream();
  }
}

// Create an instance of your class
final ClassName _className = ClassName();

// Add a listener
_className.addListener((T event) {
  // Handle the event...
});

// Notify listeners of an event
_className.notifyListeners(eventData);

// Remove a listener
_className.removeListener();

// Dispose of your class. Alternatively call `ClassName.closeStream()` directly
// if nothing else from the class needs to be cancelled/closed/disposed.
_className.dispose();

Using with Flutter

BroadcastStreamSubscriber can be used within Flutter widgets to listen for events from any class that mixes it in.

To properly subscribe to events and dispose of the notifier when finished, BroadcastStreamSubscriber's methods should be implemented from within a StatefulWidget, or rather its State.

  import 'package:flutter/material.dart';
  import 'package:broadcast_stream_subscriber/broadcast_stream_subscriber.dart';

  class ListenableClass with BroadcastStreamSubscriber<String> {
    ListenableClass();

    //

    void dispose() => closeStream();
  }

  class MyWidget extends StatefulWidget {
    @override
    _MyWidgetState createState() => _MyWidgetState();
  }

  class _MyWidgetState extends State<MyWidget> {
    final ListenableClass _listenableClass = ListenableClass();

    StreamSubscription<String> _onEvent;

    String _eventData;

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

    @override
    void dispose() {
      _onEvent.cancel();
      _listenableClass.closeStream();
      super.dispose();
    }

    void _listenForEvents() {
      _onEvent = _listenableClass.addListener((String event) {
        setState(() => _eventData = event);
      });
    }

    @override
    Widget build(BuildContext context) {
      return Text(_eventData ?? 'No event data recieved');
    }
  }

If a listenable class is inherited by a nested widget, the State's didUpdateWidget method should be utilized to detect and handle any changes to the listener.

And, rather than calling closeStream on dispose(), removeListener should instead be used. closeStream should be called from within the parent.

  class MyWidget extends StatefulWidget {
    const MyWidget(this.listenableClass);

    final ListenableClass listenableClass;

    @override
    _MyWidgetState createState() => _MyWidgetState();
  }

  class _MyWidgetState extends State<MyWidget> {
    StreamSubscription<String> _onEvent;

    String _eventData;

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

    @override
    void dispose() {
      _onEvent?.cancel();
      widget.listenableClass?.removeListener();
      super.dispose();
    }

    @override
    void didUpdateWidget(MyWidget old) {
      if (widget.listenableClass != old.listenableClass) {
        _onEvent?.cancel();
        _listenForEvents();
      }

      super.didUpdateWidget(old);
    }

    void _listenForEvents() {
      if (widget.listenableClass == null) return;

      _onEvent = widget.listenableClass.addListener((String event) {
        setState(() => _eventData = event);
      });
    }

    @override
    Widget build(BuildContext context) {
      return Text(_eventData ?? 'No event data recieved');
    }
  }