dart - 父类的功能需要检测对子类属性的更改

Question

我正在尝试为此父“Persistent”类添加功能的方法，以便无论何时更改子对象的任何属性，“changed”属性都将变为true。

class Persistent {
  bool changed = false;

  Persistent() {
    print('Something should be added here to make this work.');
  }
}

class Child extends Persistent {
  num number = 1;
  // Nothing should be done in this class to make this work.
}

main() {
  Child item = new Child();
  item.number = 2;
  assert(item.changed == true); //fails
}

要求:目标是使此子类透明。检测变化的功能一定不能在Child类中存在，而只能在Persistent类内部存在。

感谢Dart专家的帮助!我期待着您的回音。

这是使该工作正常进行的工作:

import 'dart:io';
import 'dart:async';
import 'dart:convert';
import 'package:observe/observe.dart';

class Persistent extends Object with ChangeNotifier {
  bool changed = false;

  Persistent() {
    this.changes.listen((List<ChangeRecord> record) => changed = false);
    //this.changes.listen((List<ChangeRecord> record) => changed = true); //Same exception
  }
}

class Child extends Persistent {
  @observable num number = 1;
  // Nothing should be done in this class to make this work.
}

main() {
  Child item = new Child();
  item.number = 2;
  assert(item.changed == true);
}

上面给了我以下异常(exception):

Unhandled exception:
'file:///home/david/Dropbox/WebDevelopment/DODB/source/DODB/bin/dodb.dart': Failed assertion: line 22 pos 10: 'item.changed == true' is not true.
#0      main (file:///home/david/Dropbox/WebDevelopment/DODB/source/DODB/bin/dodb.dart:22:10)
#1      _startIsolate.isolateStartHandler (dart:isolate-patch/isolate_patch.dart:216)
#2      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:124)

Answer 1

您可以使用ChangeNotifier类，如该问题的答案中所示

Observe package from polymer dart

How to use Dart ChangeNotifier class?
另请参阅

https://api.dartlang.org/apidocs/channels/be/dartdoc-viewer/observe/observe.ChangeNotifier

https://api.dartlang.org/apidocs/channels/be/dartdoc-viewer/observe/observe.Observable

另一种尝试是使用反射，但是尤其在浏览器中不建议这样做。
上面的解决方案也使用反射，但是据我所知，Smoke转换器生成的代码会在运行 pub build时替换反射代码。
编辑

仅在调用 Observable.dirtyCheck();之后，才会启动更改检测(对于所有可观察的实例)。

import 'package:observe/observe.dart';

class Persistent extends Observable {
  bool changed = false;

  Persistent() : super() {
    changes.listen((e) => changed = true);
  }
}

class Child extends Persistent {
  @observable num number = 1;
}

main() {
  Child item = new Child();
  item.number = 2;
  Observable.dirtyCheck();
  assert(item.changed == true);
}