public static void ItemIndexDecrement <T>(this NotifiableCollection <T> collection, T item, int count = 1)
{
if (collection != null)
{
collection.Move(collection.IndexOf(item), count);
}
}
public static void ItemIndexIncrement <T>(this NotifiableCollection <T> collection, int oldIndex, int count = 1)
{
collection.Move(oldIndex, oldIndex + count);
}