Implementing COM OutOfProc Servers in C# .NET !!!

Had to implement our COM OOP Server project in .NET, and I found this solution from the internet after a great deal of search, but unfortunately the whole idea was ruled out, and we wrapped it as a .NET assembly. This is worth knowing.

Step 1:
Implement IClassFactory in a class in .NET. Use the following definition for IClassFactory.

namespace COM
static class Guids
public const string IClassFactory = "00000001-0000-0000-C000-000000000046";
public const string IUnknown = "00000000-0000-0000-C000-000000000046";

/// IClassFactory declaration
[ComImport(), InterfaceType(ComInterfaceType.InterfaceIsIUnknown), Guid(COM.Guids.IClassFactory)]
internal interface IClassFactory
int CreateInstance(IntPtr pUnkOuter, ref Guid riid, out IntPtr ppvObject);
int LockServer(bool fLock);

Step 2:

private static extern int CoRegisterClassObject(ref Guid rclsid,
[MarshalAs(UnmanagedType.Interface)]IClassFactory pUnkn,
int dwClsContext,
int flags,
out int lpdwRegister);

private static extern int CoRevokeClassObject(int dwRegister);

Step 3:
Use these functions to register your own IClassFactory

Step 4:
IClassFactory has a CreateInstance method. Implement this method to return a reference (IntPtr) to your own object. Use Marshal.GetIUnknownForObject to get IUnknown pointer to your object.

Step 5:
The COM client receives a pointer to this object, and can use it as a regular COM object. .NET does the reference counting for you, and the GC will collect these objects when the COM-reference-count decremetns to zero.

Walking through and closely examining the working of ClassFactories for COM will give a clear sight of the objects that you need to implement in .NET, and a solution for COM Server in managed world.

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