如何在Dart / Polymer Dart中创建可观察的导数属性？ [英] How do you create an observable derivative property in Dart / Polymer Dart?

问题描述

我有一个组件，我想绑定一个不同的CSS类基于一个布尔值。我在我的组件代码中有以下：

  bindCssClass（div，open，this，task.isOpen）; 
 bindCssClass（div，closed，this，'task.isClosed'）; 
  

isOpen / isClosed的定义如下：

  @observable bool isOpen = true; 
 get isClosed => ！开了;问题是，如何获得isClosed是可观察的，但是基于对isOpen的更改吗？我想知道这种情况，但也适用于更复杂的情况（例如，从多个组件派生的字符串）
 
 
 
此外，有更好的方法使用bindCss这样一个简单的case？绑定到'！task.isOpen'不工作，虽然它会很好，如果它是。
解决方案
以检查来自dart-polymer-dart-examples github repo的observable_getter示例。
  with ObservableMixin {
 @observable 
 DateTime timestamp; 
 
 App（）{
 bindProperty（this，const Symbol（'timestamp'），
（）=> notifyProperty（this，const Symbol（'second'）） ; 
} 
 
 int get second => timestamp.second; 
} 
 
 
 main（）{
 App app = new App（）; 
 new Timer.periodic（const Duration（seconds：1），（_）{
 app.timestamp = new DateTime.now（）; 
}）; 
 query（'＃tmpl'）。model = app; 
} 
  
同时检查 https://code.google.com/p/dart/issues/detail?id=12473  
 
I have a component that I want to bind a different css class to based on a boolean value.  I have the following in my component code:
bindCssClass(div, "open", this, "task.isOpen");
bindCssClass(div, "closed", this, 'task.isClosed');
Where isOpen / isClosed are defined as the following:
@observable bool isOpen = true;
get isClosed => !isOpen;
The question is, how can I get isClosed to be observable, but based on changes to isOpen?  I'd like to know this case, but also for cases that are more complicated (e.g. a string that is derived from multiple components)

Additionally, is there a better way to use bindCss for such a simple case? Binding to '!task.isOpen' doesn't work, though it would be nice if it did.
解决方案
you may want to check observable_getter example from dart-polymer-dart-examples github repo.
class App extends Object with ObservableMixin {
  @observable
  DateTime timestamp;

  App() {
    bindProperty(this, const Symbol('timestamp'),
      () => notifyProperty(this, const Symbol('second')));
  }

  int get second => timestamp.second;
}


main() {
  App app = new App();
  new Timer.periodic(const Duration(seconds: 1), (_) {
    app.timestamp = new DateTime.now();
  });
  query('#tmpl').model = app;
}
Also check discussion at: https://code.google.com/p/dart/issues/detail?id=12473

                        
这篇关于如何在Dart / Polymer Dart中创建可观察的导数属性？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！