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
{
[PreserveSig]
int CreateInstance(IntPtr pUnkOuter, ref Guid riid, out IntPtr ppvObject);
[PreserveSig]
int LockServer(bool fLock);
}
}

Step 2:

[DllImport("ole32.dll")]
private static extern int CoRegisterClassObject(ref Guid rclsid,
[MarshalAs(UnmanagedType.Interface)]IClassFactory pUnkn,
int dwClsContext,
int flags,
out int lpdwRegister);

[DllImport("ole32.dll")]
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.

Advertisements

4 thoughts on “Implementing COM OutOfProc Servers in C# .NET !!!”

  1. Thanks a lot. Can you provide more about how to implement the IClassFactory. I tried to call Marshal.GetIUnknownForObject but Calling from native client always invokes to wrong method of .net object.CallingMarshal.GetComInterfaceForObject seems to work: public void CreateInstance(object pUnkOuter, Guid riid, out IntPtr ppvObject) { ppvObject = Marshal.GetComInterfaceForObject(theObject, typeof(IDynRange)); // works // ppvObject = Marshal.GetIUnknownForObject(theObject as IDynRange); // does not work }ilatavor@gmail.com

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s