How can I listen for changes to properties on objects inside a list, with polymer-dart?

Question

I have a list of objects (for example, people), and I dynamically add and remove from the list. I want to run a query across the list when a certain property changes on any item

Answer 1

Enter: ListPathObserver!

Add this constructor:

  MyElement() {
    ListPathObserver observer = new ListPathObserver(people, 'signedAgreement');
    observer.changes.listen((_) => notifyProperty(this, const Symbol('signedCount')));
  }

Here, observer will fire when any person in people has its signedAgreement property changed.

Then, in the callback, we notify the observer system that it should go look at signedCount.