How to observe simple variable in dart language
(This answer applies to Polymer.dart.)
The observe package includes a wrapper for single observable values: ObservableBox.
import 'package:observe/observe.dart';import 'dart:async';void main() { ObservableBox myValue = new ObservableBox('hello'); myValue.changes.listen((List<ChangeRecord> records) { PropertyChangeRecord record = records[0] as PropertyChangeRecord; print('${record.field} changed, it is now ${myValue.value}'); }); new Timer.periodic(const Duration(seconds: 1), (t) { myValue.value = new DateTime.now(); });}There is no way to observe a top-level or function-scope single string, boolean, int, or double without using ObservableBox.
If the string, boolean, int, or double is a field of a class, you can use ObservableMixin and the @observable annotation.
class Foo extends Object with ObservableMixin { @observable String bar = '';}You can then get notified when an instance of Foo changes:
foo.changes.listen((List<ChangeRecord> records) { // ...});
Here is an example of the binding of a string value that is object attribute:
<!DOCTYPE html><html> <head> <title>index</title> <script src="packages/polymer/boot.js"></script> </head> <body> <template id="_template" bind> <input type="text" value="{{name}}"> <p>The name is {{name}}</p> </template> <script type="application/dart" src="index.dart"></script> </body></html>import 'dart:html';import 'package:polymer/polymer.dart';class Person extends Object with ObservableMixin { @observable String name; Person(this.name);}main() { query("#_template").model = new Person('Bob');}