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| 1 // Copyright (c) 2013, the Dart project authors. Please see the AUTHORS file | |
| 2 // for details. All rights reserved. Use of this source code is governed by a | |
| 3 // BSD-style license that can be found in the LICENSE file. | |
| 4 | |
| 5 library observe.src.observable; | |
| 6 | |
| 7 import 'dart:async'; | |
| 8 import 'dart:collection'; | |
| 9 | |
| 10 import 'package:smoke/smoke.dart' as smoke; | |
| 11 import 'package:observe/observe.dart'; | |
| 12 | |
| 13 // Note: this is an internal library so we can import it from tests. | |
| 14 // TODO(jmesserly): ideally we could import this with a prefix, but it caused | |
| 15 // strange problems on the VM when I tested out the dirty-checking example | |
| 16 // above. | |
| 17 import 'dirty_check.dart'; | |
| 18 | |
| 19 /// Represents an object with observable properties. This is used by data in | |
| 20 /// model-view architectures to notify interested parties of [changes] to the | |
| 21 /// object's properties (fields or getter/setter pairs). | |
| 22 /// | |
| 23 /// The interface does not require any specific technique to implement | |
| 24 /// observability. You can implement it in the following ways: | |
| 25 /// | |
| 26 /// - extend or mixin this class, and let the application call [dirtyCheck] | |
| 27 /// periodically to check for changes to your object. | |
| 28 /// - extend or mixin [ChangeNotifier], and implement change notifications | |
| 29 /// manually by calling [notifyPropertyChange] from your setters. | |
| 30 /// - implement this interface and provide your own implementation. | |
| 31 abstract class Observable { | |
| 32 /// Performs dirty checking of objects that inherit from [Observable]. | |
| 33 /// This scans all observed objects using mirrors and determines if any fields | |
| 34 /// have changed. If they have, it delivers the changes for the object. | |
| 35 static void dirtyCheck() => dirtyCheckObservables(); | |
| 36 | |
| 37 StreamController _changes; | |
| 38 | |
| 39 Map<Symbol, Object> _values; | |
| 40 List<ChangeRecord> _records; | |
| 41 | |
| 42 /// The stream of change records to this object. Records will be delivered | |
| 43 /// asynchronously. | |
| 44 /// | |
| 45 /// [deliverChanges] can be called to force synchronous delivery. | |
| 46 Stream<List<ChangeRecord>> get changes { | |
| 47 if (_changes == null) { | |
| 48 _changes = new StreamController.broadcast(sync: true, | |
| 49 onListen: _observed, onCancel: _unobserved); | |
| 50 } | |
| 51 return _changes.stream; | |
| 52 } | |
| 53 | |
| 54 /// True if this object has any observers, and should call | |
| 55 /// [notifyChange] for changes. | |
| 56 bool get hasObservers => _changes != null && _changes.hasListener; | |
| 57 | |
| 58 void _observed() { | |
| 59 // Register this object for dirty checking purposes. | |
| 60 registerObservable(this); | |
| 61 | |
| 62 var values = new Map<Symbol, Object>(); | |
| 63 | |
| 64 // Note: we scan for @observable regardless of whether the base type | |
| 65 // actually includes this mixin. While perhaps too inclusive, it lets us | |
| 66 // avoid complex logic that walks "with" and "implements" clauses. | |
| 67 var queryOptions = new smoke.QueryOptions(includeInherited: true, | |
| 68 includeProperties: false, withAnnotations: const [ObservableProperty]); | |
| 69 for (var decl in smoke.query(this.runtimeType, queryOptions)) { | |
| 70 var name = decl.name; | |
| 71 // Note: since this is a field, getting the value shouldn't execute | |
| 72 // user code, so we don't need to worry about errors. | |
| 73 values[name] = smoke.read(this, name); | |
| 74 } | |
| 75 | |
| 76 _values = values; | |
| 77 } | |
| 78 | |
| 79 /// Release data associated with observation. | |
| 80 void _unobserved() { | |
| 81 // Note: we don't need to explicitly unregister from the dirty check list. | |
| 82 // This will happen automatically at the next call to dirtyCheck. | |
| 83 if (_values != null) { | |
| 84 _values = null; | |
| 85 } | |
| 86 } | |
| 87 | |
| 88 /// Synchronously deliver pending [changes]. Returns true if any records were | |
| 89 /// delivered, otherwise false. | |
| 90 // TODO(jmesserly): this is a bit different from the ES Harmony version, which | |
| 91 // allows delivery of changes to a particular observer: | |
| 92 // http://wiki.ecmascript.org/doku.php?id=harmony:observe#object.deliverchange
records | |
| 93 // | |
| 94 // The rationale for that, and for async delivery in general, is the principal | |
| 95 // that you shouldn't run code (observers) when it doesn't expect to be run. | |
| 96 // If you do that, you risk violating invariants that the code assumes. | |
| 97 // | |
| 98 // For this reason, we need to match the ES Harmony version. The way we can do | |
| 99 // this in Dart is to add a method on StreamSubscription (possibly by | |
| 100 // subclassing Stream* types) that immediately delivers records for only | |
| 101 // that subscription. Alternatively, we could consider using something other | |
| 102 // than Stream to deliver the multicast change records, and provide an | |
| 103 // Observable->Stream adapter. | |
| 104 // | |
| 105 // Also: we should be delivering changes to the observer (subscription) based | |
| 106 // on the birth order of the observer. This is for compatibility with ES | |
| 107 // Harmony as well as predictability for app developers. | |
| 108 bool deliverChanges() { | |
| 109 if (_values == null || !hasObservers) return false; | |
| 110 | |
| 111 // Start with manually notified records (computed properties, etc), | |
| 112 // then scan all fields for additional changes. | |
| 113 List records = _records; | |
| 114 _records = null; | |
| 115 | |
| 116 _values.forEach((name, oldValue) { | |
| 117 var newValue = smoke.read(this, name); | |
| 118 if (oldValue != newValue) { | |
| 119 if (records == null) records = []; | |
| 120 records.add(new PropertyChangeRecord(this, name, oldValue, newValue)); | |
| 121 _values[name] = newValue; | |
| 122 } | |
| 123 }); | |
| 124 | |
| 125 if (records == null) return false; | |
| 126 | |
| 127 _changes.add(new UnmodifiableListView<ChangeRecord>(records)); | |
| 128 return true; | |
| 129 } | |
| 130 | |
| 131 /// Notify that the field [name] of this object has been changed. | |
| 132 /// | |
| 133 /// The [oldValue] and [newValue] are also recorded. If the two values are | |
| 134 /// equal, no change will be recorded. | |
| 135 /// | |
| 136 /// For convenience this returns [newValue]. | |
| 137 notifyPropertyChange(Symbol field, Object oldValue, Object newValue) | |
| 138 => notifyPropertyChangeHelper(this, field, oldValue, newValue); | |
| 139 | |
| 140 /// Notify observers of a change. | |
| 141 /// | |
| 142 /// For most objects [Observable.notifyPropertyChange] is more convenient, but | |
| 143 /// collections sometimes deliver other types of changes such as a | |
| 144 /// [ListChangeRecord]. | |
| 145 /// | |
| 146 /// Notes: | |
| 147 /// - This is *not* required for fields if you mixin or extend [Observable], | |
| 148 /// but you can use it for computed properties. | |
| 149 /// - Unlike [ChangeNotifier] this will not schedule [deliverChanges]; use | |
| 150 /// [Observable.dirtyCheck] instead. | |
| 151 void notifyChange(ChangeRecord record) { | |
| 152 if (!hasObservers) return; | |
| 153 | |
| 154 if (_records == null) _records = []; | |
| 155 _records.add(record); | |
| 156 } | |
| 157 } | |
| 158 | |
| 159 // TODO(jmesserly): remove the instance method and make this top-level method | |
| 160 // public instead? | |
| 161 // NOTE: this is not exported publically. | |
| 162 notifyPropertyChangeHelper(Observable obj, Symbol field, Object oldValue, | |
| 163 Object newValue) { | |
| 164 | |
| 165 if (obj.hasObservers && oldValue != newValue) { | |
| 166 obj.notifyChange(new PropertyChangeRecord(obj, field, oldValue, newValue)); | |
| 167 } | |
| 168 return newValue; | |
| 169 } | |
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Chromium Code Reviews
Issue 817483003:
delete observe from the repo (Closed)
Base URL: https://dart.googlecode.com/svn/branches/bleeding_edge/dart