event_bus 1.1.0

Event Bus #

A simple Event Bus using Dart Streams for decoupling applications.

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Event Bus Pattern #

An Event Bus follows the publish/subscribe pattern. It allows listeners to subscribe for events and publishers to fire events. This enables objects to interact without requiring to explicitly define listeners and keeping track of them.

Event Bus and MVC #

The Event Bus pattern is especially helpful for decoupling MVC (or MVP) applications.

One group of MVC is not a problem.


But as soon as there are multiple groups of MVCs, those groups will have to talk to each other. This creates a tight coupling between the controllers.

Multi Model-View-Controllers

By communication through an Event Bus, the coupling is reduced.

Event Bus

Usage #

1. Create an Event Bus #

Create an instance of EventBus and make it available to other classes.

Usually there is just one Event Bus per application, but more than one may be set up to group a specific set of events.

import 'package:event_bus/event_bus.dart';

EventBus eventBus = EventBus();

Note: The default constructor will create an asynchronous event bus. To create a synchronous bus you must provide the optional sync: true attribute.

2. Define Events #

Any Dart class can be used as an event.

class UserLoggedInEvent {
  User user;


class NewOrderEvent {
  Order order;


3. Register Listeners #

Register listeners for specific events:

eventBus.on<UserLoggedInEvent>().listen((event) {
  // All events are of type UserLoggedInEvent (or subtypes of it).

Register listeners for all events:

eventBus.on().listen((event) {
  // Print the runtime type. Such a set up could be used for logging.

About Dart Streams #

EventBus uses Dart Streams as its underlying mechanism to keep track of listeners. You may use all functionality available by the Stream API. One example is the use of StreamSubscriptions to later unsubscribe from the events.

StreamSubscription loginSubscription = eventBus.on<UserLoggedInEvent>().listen((event) {


4. Fire Events #

Finally, we need to fire an event.

User myUser = User('Mickey');

Using Custom Stream Controllers #

Instead of using the default StreamController you can use the following constructor to provide your own.

An example would be to use an RxDart Subject as the controller.

import 'package:rxdart/rxdart.dart';

EventBus behaviorBus = EventBus.customController(BehaviorSubject());

Running / Building / Testing #

  • Run from the terminal: webdev serve
  • Build from the terminal: webdev build
  • Testing: pub run build_runner test -- -p chrome

License #

The MIT License (MIT)

Changelog #

Version 1.1.0 (2019-03-27) #

  • Add constructor for custom controllers like RxDart Subject (see #21).
  • Remove new keyword.

Version 1.0.3 (2019-02-14) #

  • Cleanup and update dependencies.

Version 1.0.0 (2018-07-06) #

  • Migrate to Dart 2.
  • BREAKING CHANGE: The on method now has a generic type. The type must be passed as a type argument instead of a method parameter. Change myEventBus.on(MyEventType) to myEventBus.on<MyEventType>().
  • BREAKING CHANGE: Every EventBus is now hierarchical so that listeners will also receive events of subtypes of the specified type. This is exactly the way that HierarchicalEventBus worked. So HierarchicalEventBus has been removed. Use the normal EventBus instead.

Version 0.4.1 (2015-05-13) #

  • Fix Issue #13: Improve on() stream when no type is specified

Version 0.4.0 (2015-05-03) #

  • BREAKING CHANGE: Moved the HierarchicalEventBus to a separate library to be able to remove dart:mirrors from the normal EventBus.
    Users of the hierarchical event bus must import event_bus_hierarchical.dart and replace the use of the factory constructor EventBus.hierarchical() with the HierarchicalEventBus constructor.

Version 0.3.0 (2014-09-08) #

  • BREAKING CHANGE: Changed and simplified the EventBus API. We can now dispatch any Dart object as an event. Before, we had to create an EventType for every type of event we wanted to fire. Now we can use any class as an event. Listeners can (optionally) filter events by that class.
  • Added a way to create a hierarchical event bus that filters events by class and their subclasses. This currently only works with classes extending other classes and not with implementing an interface. We might have to wait for https://code.google.com/p/dart/issues/detail?id=20756 to enable interfaces.
  • BREAKING CHANGE: The EventBus constructor defaults to async instead of sync!!. This matches the constructor of the Dart Streams and an async event bus might also be the more common use case.
  • BREAKING CHANGE: Removed LoggingEventBus. Reason is that logging can easily be implemented with a event listener that listens for all events and logs them.

Version 0.2.5 (2014-09-03) #

  • Update example.
  • Update readme with new links.
  • Update dependencies.

Version 0.2.4 (2013-11-11) #

  • Update to dart libraries 0.9.0.

Version 0.2.3 (2013-09-16) #

  • Fix issue #8: Add logging of events that flow through event bus

Version 0.2.2 (2013-09-16) #

  • Change default of SimpleEventBus to sync (same as factory in EventBus)

Version 0.2.1 (2013-07-01) #

  • Fix issue #6: Fire should accept null as data

Version 0.2.0 (2013-06-06) #

  • Update to new Dart SDK v0.5.13.1_r23552.
  • Using Darts new Stream.broadcast() factory.
  • Provide option for synchronous broadcasting of events.
  • Update unit tests and example.
  • Create demo page.

Version 0.1.3 (2013-05-19) #

  • Removed all occurrences of @override

Version 0.1.2 (2013-05-17) #

  • Change in README: contained wrong license (Apache instead of MIT).
  • Remove import 'package:meta/meta.dart' in event_bus.dart as it is not needed and may cause an error if used as pub package.

Version 0.1.1 (2013-04-29) #

  • Minor change in README to fix image links.

Version 0.1.0 (2013-04-29) #

  • Initial Version.


import 'dart:async';
import 'dart:html';

import 'package:logging/logging.dart';

import 'events.dart';

int counterA = 1;
int counterB = 1;

final _log = Logger('event_bus_example');

void main() {
  // Init logging.

  // Log all events.
      .listen((event) => _log.finest('event fired:  ${event.runtimeType}'));

  // Initialize the listener boxes.

  // Init Event fields.
  LabelElement fireLabelA = querySelector('#fire-label-a');
  LabelElement fireLabelB = querySelector('#fire-label-b');
  ButtonElement fireButtonA = querySelector("#fire-button-a");
  ButtonElement fireButtonB = querySelector("#fire-button-b");

  fireButtonA.onClick.listen((_) {
    // -------------------------------------------------
    // Fire Event A
    // -------------------------------------------------
    eventBus.fire(MyEventA('Received Event A [$counterA]'));
    fireLabelA.text = '--> fired [$counterA]';
  fireButtonB.onClick.listen((_) {
    // -------------------------------------------------
    // Fire Event B
    // -------------------------------------------------
    eventBus.fire(MyEventB('Received Event B [$counterB]'));
    fireLabelB.text = '--> fired [$counterB]';

initLogging() {
  // Print output to console.
  Logger.root.onRecord.listen((LogRecord r) {

  // Root logger level.
  Logger.root.level = Level.FINEST;

class Listener {
  Element element;

  TextAreaElement output;

  StreamSubscription subscription;

  Listener(this.element) {
    output = element.querySelector('textarea');
    // Init buttons.
    element.querySelector('.listen-a').onClick.listen((_) => listenForEventA());
    element.querySelector('.listen-b').onClick.listen((_) => listenForEventB());
    element.querySelector('.pause').onClick.listen((_) => pause());
    element.querySelector('.resume').onClick.listen((_) => resume());
    element.querySelector('.cancel').onClick.listen((_) => cancel());

  void listenForEventA() {
    if (subscription != null) {
      appendOuput('Already listening for an event.');
    } else {
      // -------------------------------------------------
      // Listen for Event A
      // -------------------------------------------------
      subscription = eventBus.on<MyEventA>().listen((event) {
      appendOuput('Listening for Event A');

  void listenForEventB() {
    if (subscription != null) {
      appendOuput('Already listening for an event.');
    } else {
      // -------------------------------------------------
      // Listen for Event B
      // -------------------------------------------------
      subscription = eventBus.on<MyEventB>().listen((MyEventB event) {
      appendOuput('Listening for Event B');

  void pause() {
    if (subscription != null) {
      appendOuput('Subscription paused.');
    } else {
      appendOuput('No subscription, cannot pause!');

  void resume() {
    if (subscription != null) {
      appendOuput('Subscription resumed.');
    } else {
      appendOuput('No subscription, cannot resume!');

  void cancel() {
    if (subscription != null) {
      subscription = null;
      appendOuput('Subscription canceled.');
    } else {
      appendOuput('No subscription, cannot cancel!');

  void appendOuput(String text) {
    output.value += '$text\n';
    output.scrollTop = output.scrollHeight;

Use this package as a library

1. Depend on it

Add this to your package's pubspec.yaml file:

  event_bus: ^1.1.0

2. Install it

You can install packages from the command line:

with pub:

$ pub get

with Flutter:

$ flutter pub get

Alternatively, your editor might support pub get or flutter pub get. Check the docs for your editor to learn more.

3. Import it

Now in your Dart code, you can use:

import 'package:event_bus/event_bus.dart';
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Learn more about scoring.

We analyzed this package on Sep 20, 2019, and provided a score, details, and suggestions below. Analysis was completed with status completed using:

  • Dart: 2.5.0
  • pana: 0.12.21


Detected platforms: Flutter, web, other

No platform restriction found in primary library package:event_bus/event_bus.dart.


Package Constraint Resolved Available
Direct dependencies
Dart SDK >=2.0.0 <3.0.0
Dev dependencies
build_runner ^1.2.5
build_test ^0.10.3
build_web_compilers ^1.1.0
logging ^0.11.0
test ^1.5.0