Index: packages/observe/lib/src/observable.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.observable; |
- |
-import 'dart:async'; |
-import 'dart:collection'; |
- |
-import 'package:smoke/smoke.dart' as smoke; |
-import 'package:observe/observe.dart'; |
- |
-// Note: this is an internal library so we can import it from tests. |
-// TODO(jmesserly): ideally we could import this with a prefix, but it caused |
-// strange problems on the VM when I tested out the dirty-checking example |
-// above. |
-import 'dirty_check.dart'; |
- |
-/// Represents an object with observable properties. This is used by data in |
-/// model-view architectures to notify interested parties of [changes] to the |
-/// object's properties (fields or getter/setter pairs). |
-/// |
-/// The interface does not require any specific technique to implement |
-/// observability. You can implement it in the following ways: |
-/// |
-/// - extend or mixin this class, and let the application call [dirtyCheck] |
-/// periodically to check for changes to your object. |
-/// - extend or mixin [ChangeNotifier], and implement change notifications |
-/// manually by calling [notifyPropertyChange] from your setters. |
-/// - implement this interface and provide your own implementation. |
-abstract class Observable { |
- /// Performs dirty checking of objects that inherit from [Observable]. |
- /// This scans all observed objects using mirrors and determines if any fields |
- /// have changed. If they have, it delivers the changes for the object. |
- static void dirtyCheck() => dirtyCheckObservables(); |
- |
- StreamController _changes; |
- |
- Map<Symbol, Object> _values; |
- List<ChangeRecord> _records; |
- |
- /// The stream of change records to this object. Records will be delivered |
- /// asynchronously. |
- /// |
- /// [deliverChanges] can be called to force synchronous delivery. |
- Stream<List<ChangeRecord>> get changes { |
- if (_changes == null) { |
- _changes = new StreamController.broadcast(sync: true, |
- onListen: _observed, onCancel: _unobserved); |
- } |
- return _changes.stream; |
- } |
- |
- /// True if this object has any observers, and should call |
- /// [notifyChange] for changes. |
- bool get hasObservers => _changes != null && _changes.hasListener; |
- |
- void _observed() { |
- // Register this object for dirty checking purposes. |
- registerObservable(this); |
- |
- var values = new Map<Symbol, Object>(); |
- |
- // Note: we scan for @observable regardless of whether the base type |
- // actually includes this mixin. While perhaps too inclusive, it lets us |
- // avoid complex logic that walks "with" and "implements" clauses. |
- var queryOptions = new smoke.QueryOptions(includeInherited: true, |
- includeProperties: false, withAnnotations: const [ObservableProperty]); |
- for (var decl in smoke.query(this.runtimeType, queryOptions)) { |
- var name = decl.name; |
- // Note: since this is a field, getting the value shouldn't execute |
- // user code, so we don't need to worry about errors. |
- values[name] = smoke.read(this, name); |
- } |
- |
- _values = values; |
- } |
- |
- /// Release data associated with observation. |
- void _unobserved() { |
- // Note: we don't need to explicitly unregister from the dirty check list. |
- // This will happen automatically at the next call to dirtyCheck. |
- if (_values != null) { |
- _values = null; |
- } |
- } |
- |
- /// Synchronously deliver pending [changes]. Returns true if any records were |
- /// delivered, otherwise false. |
- // TODO(jmesserly): this is a bit different from the ES Harmony version, which |
- // allows delivery of changes to a particular observer: |
- // http://wiki.ecmascript.org/doku.php?id=harmony:observe#object.deliverchangerecords |
- // |
- // The rationale for that, and for async delivery in general, is the principal |
- // that you shouldn't run code (observers) when it doesn't expect to be run. |
- // If you do that, you risk violating invariants that the code assumes. |
- // |
- // For this reason, we need to match the ES Harmony version. The way we can do |
- // this in Dart is to add a method on StreamSubscription (possibly by |
- // subclassing Stream* types) that immediately delivers records for only |
- // that subscription. Alternatively, we could consider using something other |
- // than Stream to deliver the multicast change records, and provide an |
- // Observable->Stream adapter. |
- // |
- // Also: we should be delivering changes to the observer (subscription) based |
- // on the birth order of the observer. This is for compatibility with ES |
- // Harmony as well as predictability for app developers. |
- bool deliverChanges() { |
- if (_values == null || !hasObservers) return false; |
- |
- // Start with manually notified records (computed properties, etc), |
- // then scan all fields for additional changes. |
- List records = _records; |
- _records = null; |
- |
- _values.forEach((name, oldValue) { |
- var newValue = smoke.read(this, name); |
- if (oldValue != newValue) { |
- if (records == null) records = []; |
- records.add(new PropertyChangeRecord(this, name, oldValue, newValue)); |
- _values[name] = newValue; |
- } |
- }); |
- |
- if (records == null) return false; |
- |
- _changes.add(new UnmodifiableListView<ChangeRecord>(records)); |
- return true; |
- } |
- |
- /// Notify that the field [name] of this object has been changed. |
- /// |
- /// The [oldValue] and [newValue] are also recorded. If the two values are |
- /// equal, no change will be recorded. |
- /// |
- /// For convenience this returns [newValue]. |
- notifyPropertyChange(Symbol field, Object oldValue, Object newValue) |
- => notifyPropertyChangeHelper(this, field, oldValue, newValue); |
- |
- /// Notify observers of a change. |
- /// |
- /// For most objects [Observable.notifyPropertyChange] is more convenient, but |
- /// collections sometimes deliver other types of changes such as a |
- /// [ListChangeRecord]. |
- /// |
- /// Notes: |
- /// - This is *not* required for fields if you mixin or extend [Observable], |
- /// but you can use it for computed properties. |
- /// - Unlike [ChangeNotifier] this will not schedule [deliverChanges]; use |
- /// [Observable.dirtyCheck] instead. |
- void notifyChange(ChangeRecord record) { |
- if (!hasObservers) return; |
- |
- if (_records == null) _records = []; |
- _records.add(record); |
- } |
-} |
- |
-// TODO(jmesserly): remove the instance method and make this top-level method |
-// public instead? |
-// NOTE: this is not exported publically. |
-notifyPropertyChangeHelper(Observable obj, Symbol field, Object oldValue, |
- Object newValue) { |
- |
- if (obj.hasObservers && oldValue != newValue) { |
- obj.notifyChange(new PropertyChangeRecord(obj, field, oldValue, newValue)); |
- } |
- return newValue; |
-} |