Hi,
I'm developing a .NET wrapper to access COM compound files. I've
imported all needed COM interfaces including IStorage and IEnumSTATSG
and I can successfully open a storage file using StgOpenStorage. The
problem is, when I try to enumerate the streams ans substorages
inside: IEnumSTATSTG.Next() is never giving me any STATSTG object,
althoug the HRESULT is S_OK.
Here's the interfaces:

[ComImport]
[GuidAttribute("0000000B-0000-0000-C000-000000000046")]
[InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)]
public interface IStorage
{
........

[PreserveSig]
int EnumElements(int reserved1, IntPtr reserved2, int reserved3,
[MarshalAs(UnmanagedType.Interface)] out IEnumSTATSTG ppenum);

........
}

[ComImport]
[GuidAttribute("0000000D-0000-0000-C000-000000000046")]
[InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)]
[System.Security.SuppressUnmanagedCodeSecurity]
public interface IEnumSTATSTG
{
.......
[PreserveSig]
int Next(uint celt, out STATSTG rgelt, out uint pceltFetched);
........
}

I'm importing StgOpenStorage as :

[DllImportAttribute("Ole32.dll")]
public static extern int
StgOpenStorage([MarshalAs(UnmanagedType.LPWStr)] string wcsName, IntPtr
pstgPriority, int grfMode, IntPtr snbExclude, int reserved, out
IStorage storage);

and the code where I'm trying to use it together:

IStorage storage;
IEnumSTATSTG ie;
System.Runtime.InteropServices.STATSTG statstg = new
System.Runtime.InteropServices.STATSTG();
int res0 = Ole32.StgOpenStorage("testfile.xls", IntPtr.Zero, 0x00000000
| 0x00000010 | 0x00000000, IntPtr.Zero, 0, out storage);
uint k;
int res1 = storage.EnumElements(0, IntPtr.Zero, 0, out ie);
int res2 = ie.Next(1, out statstg, out k);

As a result: res0, res1, and res2 are 0, which means the HRESULTS are
S_OK,
but the statstg is still empty, the same way k is 0 (should be 1, as
res2=0 means that ie.Next succeeded).

Is there a problem with marshalling interfaces somewhere? Please, help
me, I'm really out of any idea what could be the cause.

Luke

Hi Mattias,
Thanks for your reply. All interface methods are in Vtable Order, just
like it's given on MSDN. I don't have to declare IUnknown standard
interface methods, as I applied the
InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown) attribute,
right?

Luke

It works:) Thank you very mych, Mattias.

Luke

[quoted text, click to view]


Are you sure all interface methods are declared in the correct order?


Mattias

--
Mattias Sjögren [MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com

[quoted text, click to view]

It seems the MSDN docs have them in the wrong order. The correct order
(just like all other IEnum* interfaces) is Next, Skip, Reset, Close.


[quoted text, click to view]

Right.


Mattias

--
Mattias Sjögren [MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com