Emitters 
Emitters provides a simple mixin class, Emitter, to enable any object to emit events with arbitrary data types. It also provides a convenience mixin class, Receiver, to assist objects in managing their handler functions.
Example
import 'package:emitters/emitters.dart';
class Foo{}
class Bar{}
void main(){
var emitter = new Emitter();
emitter.on(Foo, (_) => print('Foo'));
emitter.on(Bar, (_) => print('Bar'));
emitter.emit(new Foo());
emitter.emit(new Bar());
}Example with Receiver
import 'package:emitters/emitters.dart';
class Dog extends Object with Emitter{
void bark(int volume){
emit(new Bark(volume));
}
}
class Cat extends Object with Receiver{
void dogBarkHandler(Event<Bark> event){
var bark = event.data;
if(bark.volume > 10){
print('cat running away');
}else{
print('cat not disturbed');
}
}
}
class Bark{
final int volume;
Bark(this.volume);
}
void main(){
var dog = new Dog();
var cat = new Cat();
cat.listen(dog, Bark, cat.dogBarkHandler);
dog.bark(9); // cat not disturbed
dog.bark(11); // cat running away
cat.ignoreAll();
dog.bark(11); // cat isn't listening to anything anymore
}All
There is a special Type All which allows receivers to listen for every event data type emitted by an Emitter with a single handler.
/// raw emiiter
emitter.on(All, (_) => print('handling all emitted objects'));
/// receiver equivalent
receiver.listen(emitter, All, (_) => print('handling all emitted objects'));
