| // Copyright (c) 2013, 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 observe.src.observer_transform; |
| |
| import 'package:observe/observe.dart'; |
| |
| /// ObserverTransform is used to dynamically transform observed value(s). |
| /// |
| /// var obj = new ObservableBox(10); |
| /// var observer = new PathObserver(obj, 'value'); |
| /// var transform = new ObserverTransform(observer, |
| /// (x) => x * 2, setValue: (x) => x ~/ 2); |
| /// |
| /// // Open returns the current value of 20. |
| /// transform.open((newValue) => print('new: $newValue')); |
| /// |
| /// obj.value = 20; // prints 'new: 40' async |
| /// new Future(() { |
| /// transform.value = 4; // obj.value will be 2 |
| /// }); |
| /// |
| /// ObserverTransform can also be used to reduce a set of observed values to a |
| /// single value: |
| /// |
| /// var obj = new ObservableMap.from({'a': 1, 'b': 2, 'c': 3}); |
| /// var observer = new CompoundObserver() |
| /// ..addPath(obj, 'a') |
| /// ..addPath(obj, 'b') |
| /// ..addPath(obj, 'c'); |
| /// |
| /// var transform = new ObserverTransform(observer, |
| /// (values) => values.fold(0, (x, y) => x + y)); |
| /// |
| /// // Open returns the current value of 6. |
| /// transform.open((newValue) => print('new: $newValue')); |
| /// |
| /// obj['a'] = 2; |
| /// obj['c'] = 10; // will print 'new 14' asynchronously |
| /// |
| class ObserverTransform extends Bindable { |
| Bindable _bindable; |
| Function _getTransformer, _setTransformer; |
| Function _notifyCallback; |
| var _value; |
| |
| ObserverTransform(Bindable bindable, computeValue(value), {setValue(value)}) |
| : _bindable = bindable, |
| _getTransformer = computeValue, |
| _setTransformer = setValue; |
| |
| open(callback(value)) { |
| _notifyCallback = callback; |
| _value = _getTransformer(_bindable.open(_observedCallback)); |
| return _value; |
| } |
| |
| _observedCallback(newValue) { |
| final value = _getTransformer(newValue); |
| if (value == _value) return null; |
| _value = value; |
| return _notifyCallback(value); |
| } |
| |
| void close() { |
| if (_bindable != null) _bindable.close(); |
| _bindable = null; |
| _getTransformer = null; |
| _setTransformer = null; |
| _notifyCallback = null; |
| _value = null; |
| } |
| |
| get value => _value = _getTransformer(_bindable.value); |
| |
| set value(newValue) { |
| if (_setTransformer != null) { |
| newValue = _setTransformer(newValue); |
| } |
| _bindable.value = newValue; |
| } |
| } |