2

I have a DLL Com Server, actually used only by one old Delphi exe-application.

COM Server is written many years ago (not by me) in C++ ATL. It implements callbacks (event - is it the same?) - using outgoing interface IConnectionPointImpl. Class Factory is singleton (marked with DECLARE_CLASSFACTORY_SINGLETON)

Now it is required that this COM Server have to be shared between more than one clients: both Delphi and C# (.NET 2.0, VS2008). I put it as DllSurrogate and now I can use it from multiple Delphi clients, using class inherited from TOleServer, overriding GetServer method to use always CoCreateInstance (because GetActiveObject usually fails) and it's working.

Now I need to consume it from C# WinService and I don't know from where to start. I wrote a little C# Hello-world which use WinApi CoCreateInstance and DllImport("ole32.dll") - I am able to connect to existing instance from COM Server but cannot subscribe to events.

Here is the DLL META-DATA imported by VS: enter image description here

I don't know if this is correct way. Here is aproximative code: 

using System;
using System.Collections.Generic;
using System.Text;
using SWLMLib;
using System.Runtime.InteropServices;
using System.Runtime.InteropServices.ComTypes;


namespace TestSWLM
{
    [Flags]
    enum CLSCTX : uint
    {
        //... defines here CLSCTX
    }

    class Program
    {
        [DllImport("ole32.dll", EntryPoint = "CoCreateInstance", CallingConvention = CallingConvention.StdCall)]
        static extern UInt32 CoCreateInstance([In, MarshalAs(UnmanagedType.LPStruct)] Guid rclsid,
           IntPtr pUnkOuter, UInt32 dwClsContext, [In, MarshalAs(UnmanagedType.LPStruct)] Guid riid,
           [MarshalAs(UnmanagedType.IUnknown)] out object rReturnedComObject);

        public static void AboutExpireHandler(IFeature pFeature, int HoursRemained)
        {
            Console.WriteLine("AboutExpireHandler, pFeature = {0}", pFeature.Code);        
        }

        static void Main(string[] args)
        {
            try
            {
                SWLMLib.ISWMgr lintfSWLMgr = null;

                object instance = null;
                UInt32 dwRes = CoCreateInstance(new Guid("8EAAFAD7-73F8-403B-A53B-4400E16D8EDF"), IntPtr.Zero, (uint)CLSCTX.CLSCTX_LOCAL_SERVER,
                    new Guid("00000000-0000-0000-C000-000000000046"), out instance);
                SWLMLib.SWMgrClass lSWLMgr = null;
                unsafe
                {
                    lintfSWLMgr = (instance as SWLMLib.ISWMgr);
                    Type liType = instance.GetType();
                }

                if (lintfSWLMgr != null)
                {
                    IntPtr iuknw = Marshal.GetIUnknownForObject(lintfSWLMgr);

                    IntPtr ipointer = IntPtr.Zero;
                    Guid lICPCGuid = typeof(IConnectionPointContainer).GUID;
                    Guid lICPGuid = typeof(IConnectionPoint).GUID;
                    Guid lIEv = new Guid("{C13A9D38-4BB0-465B-BF4A-487F371A5538}");
                    IConnectionPoint lCP = null;
                    IConnectionPointContainer lCPC = null;
                    Int32 r = Marshal.QueryInterface(iuknw, ref lICPCGuid, out ipointer);
                    lCPC = (IConnectionPointContainer)Marshal.GetObjectForIUnknown(ipointer);
                    lCPC.FindConnectionPoint(ref lIEv, out lCP);
                    Int32 outID;
                    lCP.Advise(???, out outID); // HERE I don't know what to do further
                    lIEvEv.FeatureAboutToExpire += AboutExpireHandler;
                }
            }
            catch (Exception E)
            {
                Console.WriteLine(E.Message);
                throw;
            }

            Console.ReadLine();
        }
    }
}

Any Advices, links and know-hows are welcome.

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5
  • You're looking for "COM Interop" A quick Google Search of that term will get you everything you need. Commented Apr 5, 2013 at 17:17
  • @RobertHarvey, I was searching for them all this day - there too many ways, or at least 2: Raw (using WinAPI) and Importing TLB wrapping COM Class - i don't know which is good for my scope, epsecially DLL Surrogate Commented Apr 5, 2013 at 17:19
  • If you have a TLB, this is the way to go, just add add a reference, and choose the TLB (using the COM tab in the Visual Studio Add Reference dialog box). Commented Apr 5, 2013 at 21:08
  • @SimonMourier, what do you mean? If <file-name>.TLB file - i don't have it, I have only DLL and sources of COM-Server... May it be generated? Commented Apr 6, 2013 at 13:38
  • Yes, it should be generated by the compilation of the COM object. Usually it's generated from the .IDL file. Commented Apr 6, 2013 at 14:52

2 Answers 2

Reset to default
1

It seems that I succeeded to connect to- and handle Events of DLL (in-proc) Com Server.

  1. I put COM Server as DLL Surrogate (HowTo here).
  2. Delphi Client Side - form my COM Wrapper Class, inheriting from TOleServer Class I overridden GetServer Method:

function TSWMgr.GetServer: IUnknown; begin OleCheck(CoCreateInstance(ServerData^.ClassId, nil, CLSCTX_LOCAL_SERVER, IUnknown, Result)); end;

  1. C# (Hello-World Client) side (after consulting some HowTos like this):

//using SWLMLib; //using System.Runtime.InteropServices; //using System.Runtime.InteropServices.ComTypes;

[Flags]
enum ReturnCode : uint
{
    S_OK = 0, S_FALSE = 1, REGDB_E_CLASSNOTREG = 0x80040154, CLASS_E_NOAGGREGATION = 0x80040110, E_NOINTERFACE = 0x80004002, E_POINTER = 0x80004003
}

[Flags]
enum CLSCTX : uint
{
    CLSCTX_INPROC_SERVER = 0x1, CLSCTX_INPROC_HANDLER = 0x2, CLSCTX_LOCAL_SERVER = 0x4,
    //... //others
    CLSCTX_ALL = CLSCTX_SERVER | CLSCTX_INPROC_HANDLER
}

/// <summary>
/// Sink Class implementig COM Server outgoing interface SWLMLib.ISWMgrEvents 
/// </summary>
[ClassInterface(ClassInterfaceType.None)]
class MySink : SWLMLib.ISWMgrEvents
{
    public void FeatureAboutToExpire(SWLMLib.IFeature pFeature, int HoursRemained)
    {
        Console.WriteLine("{0} FeatureAboutToExpire: Feature {1} Hours={2}", DateTime.Now, pFeature.Code, HoursRemained);
        Marshal.ReleaseComObject(pFeature); //WTF??? Without this line COM Server object is not released!
    }

    public void FeatureExpired(SWLMLib.IFeature pFeature)
    {
        Console.WriteLine("FeatureExpired: Feature {0}", pFeature.Code);
        Marshal.ReleaseComObject(pFeature); //Without this line COM Server object is not released!
    }
}

class Program
{
    //Import "CoCreateInstance" to play with run context of created COM-object (3rd parameter)
    [DllImport("ole32.dll", EntryPoint = "CoCreateInstance", CallingConvention = CallingConvention.StdCall)]
    static extern UInt32 CoCreateInstance([In, MarshalAs(UnmanagedType.LPStruct)] Guid rclsid,
       IntPtr pUnkOuter, UInt32 dwClsContext, [In, MarshalAs(UnmanagedType.LPStruct)] Guid riid,
       [MarshalAs(UnmanagedType.IUnknown)] out object rReturnedComObject);

    static void Main(string[] args)
    {
        try
        {
            Guid SWMgrClassObjectGuid = typeof(SWLMLib.SWMgrClass).GUID;    //{8EAAFAD7-73F8-403B-A53B-4400E16D8EDF}
            Guid IUnknownGuid = new Guid("00000000-0000-0000-C000-000000000046"); //Can it be written in more pretty style?

            SWLMLib.ISWMgr lintfSWLMgr = null;

            /* This will create IN-PROC Server because, it seems CoCreateInstance will be invoked with CLSCTX_INPROC_SERVER flag settled
            Type type = Type.GetTypeFromCLSID(SWMgrClassObjectGuid), true);
            object instance0 = Activator.CreateInstance(type);
            lintfSWLMgr = (instance0 as SWLMLib.ISWMgr); */

            Guid Ev1 = typeof(ISWMgrEvents).GUID;
            object instance = null;

            unsafe
            {
                UInt32 dwRes = CoCreateInstance(SWMgrClassObjectGuid,
                                                IntPtr.Zero,
                                                (uint)(CLSCTX.CLSCTX_LOCAL_SERVER), //if OR with CLSCTX_INPROC_SERVER then INPROC Server will be created, because of DLL COM Server
                                                IUnknownGuid,
                                                out instance);
                if (dwRes != 0)
                {
                    int iError = Marshal.GetLastWin32Error();
                    Console.WriteLine("CoCreateInstance Error = {0}, LastWin32Error = {1}", dwRes, iError);
                    return;
                }
                lintfSWLMgr = (instance as SWLMLib.ISWMgr);
            }

            if (lintfSWLMgr != null)
            {
                //lintfSWLMgr.InitializeMethod(...); //Initialize object

                //Find Connection Point for Events
                Guid ISWMgrEventsGuid = typeof(SWLMLib.ISWMgrEvents).GUID;      //{C13A9D38-4BB0-465B-BF4A-487F371A5538} Interface for Evenets Handling
                IConnectionPoint lCP = null;
                IConnectionPointContainer lCPC = (instance as IConnectionPointContainer);
                lCPC.FindConnectionPoint(ref ISWMgrEventsGuid, out lCP);

                MySink lSink = new MySink();
                Int32 dwEventsCookie;
                lCP.Advise(lSink, out dwEventsCookie);
                Console.WriteLine("Waiting for Events Handling...");
                Console.WriteLine("Press ENTER to Exit...");

                Console.ReadLine(); // Until Eneter is not hit, the events arrive properly
                //Here starting to Unsubscribe for Events and Com Objects CleanUP
                lCP.Unadvise(dwEventsCookie);
                Marshal.ReleaseComObject(lCP); 
                Marshal.ReleaseComObject(lintfSWLMgr); 
            }

        }
        catch (Exception E)
        {
            Console.WriteLine(E.Message);
            throw;
        }
    }
}

Maybe this is not the best way (like TblImp.exe and or COM Wrappers) but this raw way works.

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4 Comments

This seems pretty much OK to me. I have to admit that it was pretty hard to figure out the actual problem of yours. Hadn't I read through your example code and found (by chance) the line with the "// HERE I don't know what to do further" comment, I would have skipped your posting altogether. Maybe you should have put that in the first line of your posting, or even better into the header line.
@StuartRedmann, to be honest i didn't understand your comment. 1. Was my post too dummy or.. something else? 2. At least.. was my response somehow useful fro You?
I don't know how that happened, but I definitely did not reply to your comment but to OP's question. Maybe I don't have enough privileges to comment on questions but only on answers?
Sorry again, didn't recognize you as OP.<br>Your posting is definitely not too dummy but IMHO there is too much information that is not relevant. For me it takes too long to read through such long texts. I'd prefer a line like: "I have want to use a COM component with outgoing interfaces in my C# application but I don't know what I have to provide in IConnectionPoint.Advice (...)"
0

I think you'll want to write code like the following:

Type type = Type.GetTypeFromCLSID(coClassGuid, true);
object instance = Activator.CreateInstance(type);

You can think of this as analogous to CoCreateInstance.

The C# COM Interop way of doing QueryInterface is to do casts or use the as keyword:

IComInterface comInterface = instance as IComInterface;

This will avoid you having to use the COM APIs directly.

I'm by no means a COM Interop expert, I've just had to do a little work with it, so I'm hoping this helps you out.

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3 Comments

thanks, BUT it seems didn't help. I tried it before and it create separate new instance and from System Explorer I see that it use Dll directly, but shouldn't. Dll have to be shared between processes via DLLHOST.exe
Yeah, I forgot that about the dll surrogate. You can use this code with a 64-bit exe and a 32-bit com dll(where the com component is only registered on the 32-bit side), but I was never able to get the surrogate host to load up using this method with the same bitness.
Rather than using p/invoke you could use c++/cli.

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