/// <summary>
/// update the lookups with the new item
/// 1. create a notifier
/// 2. add to item -> notifier dictionary
/// 3. add to key -> items lookup
/// 4. add to item -> key dictionary
/// 5. attach to notifier changed event
/// </summary>
void _addItemToLookups(object item)
{
var notifier = _selectedValuePath.CreateNotifierOn(item);
_itemToNotifier.Add(item, notifier);
var key = notifier.Value;
_keyToItems.Add(key, item);
_itemToKey.Add(item, key);
notifier.Changed += Notifier_Changed;
}