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Side by Side Diff: pkg/observe/lib/src/observable.dart

Issue 817483003: delete observe from the repo (Closed) Base URL: https://dart.googlecode.com/svn/branches/bleeding_edge/dart
Patch Set: Created 6 years ago
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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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