Implementation of WPF event handlers

WPF event handlers can be scoped to the objects that are changing. For example, if there's a collection of items that changes and an event handler registered for OnChange then the event handler is invoked for any updates to the items of the collection. However, if the collection reference itself is updated via a new, this event handler subscription is lost. In such a case, it is better to add a event handler to the parent holding the collection and adding a event handler there as say OnRefreshed. This event handler should unsubscribe from the old OnChange event handler, update the new reference to the collection and add the new OnChange event handler.