COM interop with ActiveX nightmare

Hello and thanks for reading...

I am using a C++ unmanaged ActiveX (ocx) that allows me to read a
specific file format, and get data out of those.


I use C# .Net.
To use the ActiveX, I simply added it to my toolbox, and create an
instance in a form. Until there, all is good. I can read files, get
the data etc... even if I need to 'copy' the data from the unmanaged
side to the managed side.


Now where I hit a rodblock is when I try to copy the data back to the
ActiveX:
I need to pass a float[] to the COM object to then 'save' the data in
the original (proprietary) file format.
The ActiveX function in C++ is defined as


PutValue(int dataID, float* parray, uint size)


however in C#, the converted function by the ActiveX importer becomes


PutValue(int dataID, ref float parray, int size)


All the research I've done to figure out a solution leads me to
conclude that I need to Marshal the float* parameter into "IntPtr"


That's where I am stuck:
The imported library is already in managed C#, and shows as non-
editable 'MetaData', and it doesn't seem like I can override an
Interface declaration. So I don't see a way to Marshal the parameter.


So I tried to use COM interop directly, by calling the ActiveX.ocx
using [DllImport]


[DllImport(@"MyACTIVEX.ocx", EntryPoint = "#3")]
[return] int ID public static extern int Load(string
filename);


[DllImport(@"MyACTIVEX.ocx", EntryPoint = "#60")]
public static extern int PutValueEx(int ID, IntPtr pt, int
size);


I first had to figure out the entry point # in order to access the
functions, but got so far.
Now, calling the ocx directly, I get "Attempted to read or write
protected memory" error when trying to load the file.


Obviously there is something else that's being done when importing an
ActiveX through the toolbox.


I also tried to import the library directly, using AXIMP.EXE, It
created 2 DLLs. One seems to be the managed interop library I can get
the code from if I use the "/source" tag, the other is the actual COM
DLL.

Problem, if I reference the 1st DLL, or import the source in my
project, I see that it calls the second DLL that includes the actual
functions.
So I tried to use [DllImport] directly on that second DLL, but there
it is not able to find an entry point.


Using LibDump, I could see the type library information from the ocx
file, but I can't see anything one either of the 2 DLLs generated,
which leads me to think they are missing the interface definition.


So, I'm trying to figure out a way out of this mess:
Either by finding a way to override the interface in the imported
ActiveX control from the toolbox, and marshal the paramter properly

Or

By finding the way to generate the DLL properly so I can import it
directly with [DllImport]

Or

figure out what is wrong when calling the .ocx file directly with
[DllImport]


Any suggestion would be greatly appreciated.


Note:
1) I do not need any of the 'control' form features, only to load the
file, read the data, put data back in and save it.
2) I did ask the vendor for the file format, so I could read/write it
directly in C#, but I didn't get anywhere. Would have been my
preference but this is not an option.


Thansk for help !!!
.

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