difference between contenttypeorder and uniquecontenttypeorder

what is the difference between SPfolder.ContenttypeOrder and SPFolder.UniqueContentTypeOrder?

Why sometimes UniqueContentTypeOrder is null?

How do i get the contenttypes attached to a folder which are visible to this folder and in order? I thought by using开发者_如何学C UniqueContentTypeOrder, but sometimes it is set to null?

Thanks

UniqueContentTypeOrder is used to define a custom ordering for the folder. UniqueContentTypeOrder can be set to null to fall back to ContentTypeOrder (the default). This implies that when UniqueContentTypeOrder is null, you should fall back to ContentTypeOrder.

See http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.spfolder.uniquecontenttypeorder(office.12).aspx and http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.spfolder.contenttypeorder(v=office.12).aspx for more information.