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From managed Object* to unmanaged IUnknown

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Last Modified: 2013-12-03
I would like to use Extended MAPI in my C# programm, read a String-Property from a Message.

For this purpose I write a managed/unmanaged C++ DLL.

I have an Object* from mail.MAPIOBJECT which should be of the type IUnknown according to Microsoft documentation.
I need an LPMAPIPROP for HrGetOneProp(LPMAPIPROP pmp, int ulPropTag, LPVOID lppPro) which can be (I'm not sure, but I found it on a webpage) a pointer to a IUnknown.
But what are the lines between?

I tried:
     static String* GetStringProperty(Object* MAPIObject, int PropertyNumber) {
       String* Val;          
       char* bufVal;
       IntPtr pUnk = Marshal::GetIUnknownForObject(MAPIObject);
       LPMAPIPROP pMsgMAPI = (LPMAPIPROP)pUnk.ToPointer();
       if (pMsgMAPI!=0) {
         int hRes = HrGetOneProp(pMsgMAPI, PropertyNumber, (LPBYTE*)&bufVal);
         if (bufVal != 0) {
           if (hRes == 0) {
             Val = Marshal::PtrToStringUni(bufVal);
           }
           MAPIFreeBuffer(bufVal);
         }
       }
       return Val;
     }

pUnk gets a Value but pMsgMAPI/IUnknown says undefined.

Comment
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Try this code:

IUnknown *pUnk = (IUnknown*)Marshal::GetIUnknownForObject(MAPIObject).ToPointer();
LPMAPIPROP pMsgMAPI;
pUnk->QueryInterface(&pMsgMAPI); // or pUnk->QueryInterface(<GUID_OF_MAPIPROP>, (void**)&pMsgMAPI);
pUnk->Release();

Author

Commented:
I tried:

EXTERN_C const GUID DECLSPEC_SELECTANY IMAPIProp = { 0x00020303, 0, 0, {  0xC0, 0, 0, 0, 0, 0, 0, 0x46 } };
EXTERN_C const GUID DECLSPEC_SELECTANY IMAPIMessage = { 0x00020307, 0, 0, {  0xC0, 0, 0, 0, 0, 0, 0, 0x46 } };

Microsoft::Office::Interop::Outlook::MailItem * mi = ... ;
Object* MAPIObject;
MAPIObject = mi->MAPIOBJECT;

IUnknown* pUnk = (IUnknown*)Marshal::GetIUnknownForObject(MAPIObject).ToPointer();
LPMAPIPROP pMsgMAPI;
int res = pUnk->QueryInterface(IMAPIProp, (void**)&pMsgMAPI);
pUnk->Release();

res gets the value -2147467259 which is MAPI_E_CALL_FAILED

I also tried to convert mi the same way to IMAPIMessage and that returned the same error :-(
Don't you run this code in windows service or ASP page or MTS or schedulers?
look here:
INFO: Outlook Object Model Unsuitable to Run in a Windows Service
http://support.microsoft.com/default.aspx?scid=http://support.microsoft.com:80/support/kb/articles/q237/9/13.asp&NoWebContent=1

Author

Commented:
No, it dosen't.
Also
       String* Val;          
       Val = mi->get_To();
works correctly. It is only the cast of mi->MAPIOBJECT or mi that fails...
And if you write
Microsoft::Office::Interop::Outlook::MailItem * mi = ... ;
HrGetOneProp(mi->MAPIOBJECT, PropertyNumber, (LPBYTE*)&bufVal);
Do you get compile time error?

Author

Commented:
error C2440: 'type cast' : cannot convert from 'System::Object __gc *' to 'LPMAPIPROP'

Author

Commented:
I have found a solution myself:

http://www.mapilab.com/dev/mapiprop/

This is a library which allows accessing of the mapi-properties directly from .NET. It is also with sourcecode so I should be able compare how they solve this.

Author

Commented:
@Mod Please close question and refund points!
Commented:
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