Building a COM interop library for ASP Classic using 4.0 framework and Visual Studio 2010

It should be fairly straightforward to get a basic .NET assembly exposed to COM – I’ve never tried the COM Class project template, so this is the way I’ve managed it in the past:

Create a new (bog standard) .NET class library using C# or VB. Define a COM interface (replace GUIDs with your own):

[ComVisible(true)]
[Guid("8999F93E-52F6-4E29-BA64-0ADC22A1FB11")]
public interface IComm
{
    string GetMyGroups();
}

Now define a class that implements that interface (again, replace GUIDs with your own):

[ComVisible(true)]
[ClassInterface(ClassInterfaceType.None)]
[GuidAttribute("C5C5A1A8-9BFB-4CE5-B42C-4E6688F6840B")]
[ProgId("Test.Comm.1")]
public class Comm : IComm
{
    public string GetMyGroups()
    {
        var comm = new CommunicatorAPI.MessengerClass();

        var groups = comm.MyGroups as IMessengerGroups;
        return string.Join(", ", groups.OfType<IMessengerGroup>().Select(g => g.Name).ToArray());
    }
}

The Prog ID attribute on this class is what you will use to instantiate your component from ASP.

Strongly-name the assembly (Project properties -> “Signing” tab -> “Sign the assembly” -> Create a new strong name key file using the dropdown)

Now, build the assembly, and register using Regasm – if you don’t wish to register in the GAC (which i’d recommend, as not GACing keeps the deployment simpler), be sure to use the -Codebase parameter (this just adds a reg entry that tells clients where to find the assembly) – e.g:

regasm ClassLibrary2.dll /codebase "S:\Testing\ClassLibrary2\ClassLibrary2\bin\Debug\ClassLibrary2.dll"

Now you should be able to instantiate the component, and call methods on it – for example (in javascript):

var a = new ActiveXObject("Test.Comm.1");
alert(a.GetMyGroups());

When it comes to deployment, the important work that Regasm and Regsvr32 do is to write various settings into the registry, so that clients can find the COM component (based on Prog ID, or COM Class ID). All you need to do is work out what COM settings are being written when you run Regasm on your local machine, and write these to the registry on the server. You can use ProcMon to monitor what gets written to the registry when Regasm is run.

Generally speaking, you can expect to see something like this written to the registry:

[HKEY_CLASSES_ROOT\Test.Comm.1]
@="ClassLibrary2.Comm"

[HKEY_CLASSES_ROOT\Test.Comm.1\CLSID]
@="{00585504-90C8-4760-A359-67CAF08FFED1}"

[HKEY_CLASSES_ROOT\Wow6432Node\CLSID\{00585504-90C8-4760-A359-67CAF08FFED1}]
@="ClassLibrary2.Comm"

[HKEY_CLASSES_ROOT\Wow6432Node\CLSID\{00585504-90C8-4760-A359-67CAF08FFED1}\Implemented Categories]

[HKEY_CLASSES_ROOT\Wow6432Node\CLSID\{00585504-90C8-4760-A359-67CAF08FFED1}\Implemented Categories\{62C8FE65-4EBB-45e7-B440-6E39B2CDBF29}]

[HKEY_CLASSES_ROOT\Wow6432Node\CLSID\{00585504-90C8-4760-A359-67CAF08FFED1}\InprocServer32]
@="mscoree.dll"
"ThreadingModel"="Both"
"Class"="ClassLibrary2.Comm"
"Assembly"="ClassLibrary2, Version=1.0.0.0, Culture=neutral, PublicKeyToken=cf55d4e60653257a"
"RuntimeVersion"="v4.0.30319"
"CodeBase"="file:///S:/Testing/ClassLibrary2/ClassLibrary2/bin/Debug/ClassLibrary2.DLL"

[HKEY_CLASSES_ROOT\Wow6432Node\CLSID\{00585504-90C8-4760-A359-67CAF08FFED1}\InprocServer32\1.0.0.0]
"Class"="ClassLibrary2.Comm"
"Assembly"="ClassLibrary2, Version=1.0.0.0, Culture=neutral, PublicKeyToken=cf55d4e60653257a"
"RuntimeVersion"="v4.0.30319"
"CodeBase"="file:///S:/Testing/ClassLibrary2/ClassLibrary2/bin/Debug/ClassLibrary2.DLL"

[HKEY_CLASSES_ROOT\Wow6432Node\CLSID\{00585504-90C8-4760-A359-67CAF08FFED1}\ProgId]
@="Test.Comm.1"

Hope this helps 🙂

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