sky/packages/sky/lib/base/image_resource.dart

// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';
import 'dart:sky' as sky;

typedef void ImageListener(sky.Image image);

class ImageResource {
  ImageResource(this._futureImage) {
    _futureImage.then((sky.Image image) {
      _image = image;
      _resolved = true;
      _notifyListeners();
    });
  }

  bool _resolved = false;
  Future<sky.Image> _futureImage;
  sky.Image _image;
  final List<ImageListener> _listeners = new List<ImageListener>();

  Future<sky.Image> get first => _futureImage;

  void addListener(ImageListener listener) {
    _listeners.add(listener);
    if (_resolved)
      listener(_image);
  }

  void removeListener(ImageListener listener) {
    _listeners.remove(listener);
  }

  void _notifyListeners() {
    assert(_resolved);
    List<ImageListener> localListeners = new List<ImageListener>.from(_listeners);
    for (ImageListener listener in localListeners)
      listener(_image);
  }
}