Creating a listener on a list for changes

Question

I have a dart object which contains a list. Simply put:

class Test extends PolymerElement{
  List list = [];

  addTask(item){
    list.add(item);
  }
}

and I wanted to implement a listener on that list in another object:

class listenerClass extends PolymerElement {
  Test get _data => $['Object'];
}

So the object is retrieved from the dom withthe getter.

Is there a way to observe a change in the parent? I tried the following:

@Observe("_data.list")
dataListChanged(_,__){
  var item = _data.list.last;
  //do magic with item.
}

I have the underscore because it is private and isnt exposed to Dom or anything... but the list itself isnt a property so it doesnt notify or anything.

I was hoping there was a way to do some sort of listener for it though.

My desired endstate is that I want to fire a function in the parent whenever an item is added to the list, with only the reference to the child object as defined above. Even though this _data is populated by way of Polymer, Since this isnt touching properties at all, the answer may likely just be Pure dart.

Answer 1

This is not how polymer works. Polymer framework has no way to know you have defined a getter in your class and emit the right notification.

You should add notify to the list property of Test and bind that to a property in listenerClass . Then observe that variable.

But probably you will have better luck with ObservableList and using autonotify for a simpler way to use observability with polymer-dart projects.