The ItemId type is introduced to the managed APIs to represent either a POOM Oid (int) or MAPI ENTRYID (16/14 bytes). It doesn’t directly expose the underlying data but there are a couple of useful behaviours:-
- ItemId constructor accepts an int to create an ItemId from an existing known Oid value
- For POOM items (Appointment, Contact, Task) calling GetHashCode() on the ItemId returns the underlying Oid. However since this behaviour is not specifically documented it cannot be relied upon to stay this way in a future version.
- Oids on Windows Mobile 5.0 are created differently to previous versions. On older platforms the Oid is the identifier of the CEDB database record containing the item. On Windows Mobile 5.0 the databases are housed in an EDB database. Here the POOM Oid is a separate field containing a unique id and the item type, therefore it’s possible to infer the type from an Oid unlike previous versions – 0x4000001 would be an Appointment, 0x80000001 a Contact and 0xC0000001 a Task.