EventBus

event_bus.dart

// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

library core.event_bus;

import 'dart:async';

/**
 * An event bus class. Clients can listen for classes of events, optionally
 * filtered by a string type. This can be used to decouple events sources and
 * event listeners.
 */
class EventBus {
  final StreamController<BusEvent> _controller =
      new StreamController.broadcast();

  EventBus();

  /**
   * Listen for events on the event bus. Clients can pass in an optional [type],
   * which filters the events to only those specific ones.
   */
  Stream<BusEvent> onEvent([String type]) {
    if (type == null) {
      return _controller.stream;
    } else {
      return _controller.stream.where((e) => e.type == type);
    }
  }

  /**
   * Add an event to the event bus.
   */
  void addEvent(BusEvent event) => _controller.add(event);

  /**
   * Close (destroy) this [EventBus]. This is generally not used outside of a
   * testing context. All Stream listeners will be closed and the bus will not
   * fire any more events.
   */
  Future close() => _controller.close();
}

/**
 * An event type for use with [EventBus].
 */
class BusEvent {
  /// The type of the event.
  final String type;

  /// Any args associated with the event.
  final Map args;

  BusEvent(this.type, [this.args = const {}]);

  String toString() => '[${type}: ${args}]';
}

event_bus_test.dart

// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

library dart_pad.event_bus_test;

import 'dart:async';

import 'package:dart_pad/core/event_bus.dart';
import 'package:test/test.dart';

main() => defineTests();

void defineTests() {
  group('event_bus', () {
    test('fire one event', () {
      EventBus bus = new EventBus();
      Future<List> f = bus.onEvent('file-save').toList();
      _fireEvents(bus);
      bus.close();
      return f.then((List l) {
        expect(l.length, 1);
      });
    });

    test('fire two events', () {
      EventBus bus = new EventBus();
      Future<List> f = bus.onEvent('file-modified').toList();
      _fireEvents(bus);
      bus.close();
      return f.then((List l) {
        expect(l.length, 2);
        expect(l[0].args['file'], 'a');
        expect(l[1].args['file'], 'b');
      });
    });

    test('receive all events', () {
      EventBus bus = new EventBus();
      Future<List> f = bus.onEvent().toList();
      _fireEvents(bus);
      bus.close();
      return f.then((List l) {
        expect(l.length, 3);
      });
    });
  });
}

void _fireEvents(EventBus bus) {
  bus.addEvent(new BusEvent('file-save', {'file': 'a'}));
  bus.addEvent(new BusEvent('file-modified', {'file': 'a'}));
  bus.addEvent(new BusEvent('file-modified', {'file': 'b'}));
}