Property class for MVVM in Flutter

Property.dart

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

class Property<Value> implements Sink<Value> {

  Value _internalValue;
  final StreamController<Value> _streamController = StreamController.broadcast();

  Value get value {
    return _internalValue;
  }

  set value(Value newValue) {
    add(newValue);
  }

  Stream<Value> get stream {
    return _streamController.stream;
  }

  Property(this._internalValue);

  @override
  void add(Value event) {
    _internalValue = event;
    _streamController.add(event);
  }

  Widget build<V extends Widget>(V transform(Value)) {
    StreamBuilder<Value> builder = new StreamBuilder(
      stream: stream,
      builder: (context, snapshot) {
        return transform(this.value);
      }
    );
    return builder;
  }

  Property<S> map<S>(S convert(Value event)) {
    var property = Property(convert(value));
    stream.listen((value) => property.value = convert(value));
    return property;
  }

  void close() {
    _streamController.close();
  }

}