Outlook Interop：如何迭代文件夹中的所有项目

I would like to search the bodies of all outlook items. I know how to do this for the four PIM items (Notes/Tasks/Appointments/Contacts). But the code is identical for all of them with the exception of casting the COM object to the specific item type (i.e., ContactItem, AppointmentItem, etc). Is there a parent class for these PIM items, so that I can do something like this in my loop:I would like to search the bodies of all outloo