ListView not updating when adding items to it from another page

I'm trying to fill up or populate a ListView that is instantiated in PageA when the user clicks a button in PageB. I'm doing it sending a message with the MessageCenter in PageB and calling the MessageCenter.Subscribe() method in PageA (the Page where I want to add the new ViewCell or row to the ListView)... but it's not working.

I don't think that the problem is coming from the send/subscribe usage because I have alredy debugged the application and the collection (ObservableCollection) that i'm passing to the ListView.ItemSource property is indeed growning in size. Here you can see the class definitions:

PageA class definition:

PageA .xaml file:

PageB class definition:

I will appreciate a lot the help that you could provide!