Index: pkg/observe/lib/src/observer_transform.dart |
diff --git a/pkg/observe/lib/src/observer_transform.dart b/pkg/observe/lib/src/observer_transform.dart |
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index 0000000000000000000000000000000000000000..0587cd9e7a09ed3d77f0bdd8a7e4ba01a7d1301d |
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+++ b/pkg/observe/lib/src/observer_transform.dart |
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+// 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; |
+ } |
+} |