ObservableCollection and Item PropertyChanged

Here is how you would attach/detach to each item’s PropertyChanged event.

ObservableCollection<INotifyPropertyChanged> items = new ObservableCollection<INotifyPropertyChanged>();
items.CollectionChanged += items_CollectionChanged;

static void items_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
    if (e.OldItems != null)
    {
        foreach (INotifyPropertyChanged item in e.OldItems)
            item.PropertyChanged -= item_PropertyChanged;
    }
    if (e.NewItems != null)
    {
        foreach (INotifyPropertyChanged item in e.NewItems)
            item.PropertyChanged += item_PropertyChanged;
    }
}

static void item_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
    throw new NotImplementedException();
}