I have created Outlook add-in that implements my defined interface
IExposedClass (among other things for exposing some methods from add-in also).

In external app (automating Outlook):
object addInObj = isentrisAddIn.Object;
MyExcelAddin1.IExposedClass addInExposedAgain =
(MyExcelAddin1.IExposedClass)addInObj;
object temp = addInExposedAgain.GetAppointments(); // Call a method
on addin object
DataTable dt = (DataTable) objectTemp; // objectTemp is _ComObject type

calling some method, add-in that should return complex data type
(eg.DataTable). While doing cast to DataTable getting invalid cast exception.
The same result happens if I call GetAdressBookDT() method. In this case
scenarion marshaling described on various articles doesn't work as it seems
(maybe I didn't understand those articles or missed some important facts
about it).

on link
http://forums.microsoft.com/MSDN/Sho...59557&SiteID=1 there
is a good explanation what I'm trying to do.


I thought that second approach would lead me to solution of my problem but...
I defined my interface like this:

public interface IExposedClass
{
object GetAdressBook();
DataTable GetAdressBookDT();
void RefreshAdressBook();
object GetAppointments();
string Test();
DataTable GetAppointmentsDT();
void RefreshAppointments();
System.Exception LastException {get;}
bool IsInitializing {get;}
bool IsInitialized {get;}
string PluginVersion {get;}
}

For bool and string properties/methods interfacing to add-in is working
fine. But for method that should return DataTable or object, calls to
GetAppointmentsDT() are invoking _ComObject specified cast exception,
and call to GetAppointments() method thtat is returning DataTable as object,
in external app in fact is returning _ComObject type that I can't cast to
DataTable due invalid cast exception. I was trying to find code that would
help me resolve my problem doing marshaling but didn't find anything of that
type.

So my question is how can I accomplish that and do anybody have idea or code
that would help me to figure that out?

THX!