在 Dart 中实现观察者模式

这里有一个使用Observe包的方法.该示例取自该包中的代码注释(并根据上面的示例进行了调整).本质上，您使用@observable批注来批注您想要观察到的字段，然后侦听更改(通过调用Observable.dirtyCheck()来触发；

首先，将可观察到的数据包添加到pubspec.yaml中

dependencies:
  observe: any

然后创建一个快速测试程序.

import 'package:observe/observe.dart';

class MyClass extends Object with Observable {
  @observable String observedField = "Hello";

  toString() => observedField.toString(); 
}

main() {
  var obj = new MyClass();

  // anonymous function that executes when there are changes
  obj.changes.listen((records) {
    print('Changes to $obj were: $records');
  });


  obj.observedField = "Hello World";

  // No changes are delivered until we check for them
  Observable.dirtyCheck();

  print('done!');
}

这将产生以下输出:

Changes to Hello World were: [#<PropertyChangeRecord Symbol("observedField") from: Hello to: Hello World>]
done!

Update回应 comments ...

class MyClass2 extends Object with ChangeNotifier {

  String _observedField = "Hello";

  @reflectable get observedField    => _observedField;
  @reflectable set observedField(v) {
    _observedField = notifyPropertyChange(#observedField, _observedField, v);    
  }

  toString() => observedField;

}