How do I get notified when something is added or removed from an observable list in Dart?

Question

I have an observable list from Polymer and Dart. I want a getter to run when something is added or removed from the list. How do I do that?

My list:

final ObservableList masterList = toObservable([]);

My getter:

List get subList => masterList.where((item) => item.isDone);

When I add or remove from masterList , I want subList to update the view.

Answer 1

Use changes to listen for any changes to an observable object. You can put this into the created() lifecycle callback:

class Example extends PolymerElement with ObservableMixin {
  final ObservableList masterList = toObservable([]);
  created() {
    masterList.changes.listen((List<ChangeRecord> changes) {
      notifyProperty(this, const Symbol('subList'));
    }
  }

  List get subList => masterList.where((item) => item.isDone);
}

It's important to remember that changes is watching for additions and removals from the masterList . You probably don't want the typical bindProperty pattern because that just watches for changes to the variable itself (if the variable is set to a different object, then bindProperty will run).