pkg/observe/lib/src/compound_path_observer.dart - Issue 132403010: big update to observe, template_binding, polymer

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Issue 132403010: big update to observe, template_binding, polymer (Closed) Base URL: https://dart.googlecode.com/svn/branches/bleeding_edge/dart

Patch Set: Created 6 years, 10 months 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.compound_path_observer;

6

7 import 'dart:async';

8 import 'package:observe/observe.dart';

9

10 /**

11 * CompoundPathObserver is an object which knows how to listen to multiple path

12 * values (registered via [addPath]) and invoke a function when one or more

13 * of the values have changed. The result of this function will be set into the

14 * [value] property. When any value has changed, all current values are provided

15 * to the function in the single `values` argument.

16 *

17 * For example:

18 *

19 * var binding = new CompoundPathObserver(computeValue: (values) {

20 * var combinedValue;

21 * // compute combinedValue based on the current values which are provided

22 * return combinedValue;

23 * });

24 * binding.addPath(obj1, path1);

25 * binding.addPath(obj2, path2);

26 * //...

27 * binding.addPath(objN, pathN);

28 */

29 // TODO(jmesserly): this isn't a full port of CompoundPathObserver. It is only

30 // what was needed for TemplateBinding.

31 class CompoundPathObserver extends ChangeNotifier {

32 List<PathObserver> _observers = [];

33 List<StreamSubscription> _subs = [];

34 Object _value; // the last computed value

35

36 // TODO(jmesserly): this is public in observe.js

37 final Function _computeValue;

38

39 bool _started = false;

40

41 /** True if [start] has been called, otherwise false. */

42 bool get started => _started;

43

44 bool _scheduled = false;

45

46 /**

47 * Creates a new observer, optionally proving the [computeValue] function

48 * for computing the value. You can also set [schedule] to true if you plan

49 * to invoke [resolve] manually after initial construction of the binding.

50 */

51 CompoundPathObserver({computeValue(List values)})

52 : _computeValue = computeValue;

53

54 int get length => _observers.length;

55

56 @reflectable get value => _value;

57

58 void addPath(model, String path) {

59 if (_started) {

60 throw new StateError('Cannot add more paths once started.');

61 }

62

63 _observers.add(new PathObserver(model, path));

64 }

65

66 void start() {

67 if (_started) return;

68 _started = true;

69

70 final scheduleResolve = _scheduleResolve;

71 for (var observer in _observers) {

72 _subs.add(observer.changes.listen(scheduleResolve));

73 }

74 _resolve();

75 }

76

77 // TODO(rafaelw): Is this the right processing model?

78 // TODO(rafaelw): Consider having a seperate ChangeSummary for

79 // CompoundBindings so to excess dirtyChecks.

80 void _scheduleResolve(_) {

81 if (_scheduled) return;

82 _scheduled = true;

83 scheduleMicrotask(_resolve);

84 }

85

86 void _resolve() {

87 _scheduled = false;

88 if (_observers.isEmpty) return;

89 var newValue = _observers.map((o) => o.value).toList();

90 if (_computeValue != null) newValue = _computeValue(newValue);

91 _value = notifyPropertyChange(#value, _value, newValue);

92 }

93

94 /**

95 * Closes the observer.

96 *

97 * This happens automatically if the [value] property is no longer observed,

98 * but this can also be called explicitly.

99 */

100 void close() {

101 if (_observers.isEmpty) return;

102

103 if (_started) {

104 for (StreamSubscription sub in _subs) {

105 sub.cancel();

106 }

107 }

108 _observers.clear();

109 _subs.clear();

110 _value = null;

111 }

112

113 observed() => start();

114 unobserved() => close();

115 }

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