Load a .NET assembly from a COM ProgID without creating a COM object

Question

A bit of an odd question and probably backwards from what most people want to do, but I'm trying to work around a legacy COM issue.

I have two components, both of which are actually .NET assemblies, but for historical reasons one is loading the other as a COM object (the assembly is registered for COM Interop). It's a plug-in architecture where the plug-in is identified by its COM ProgID, so that's the only piece of information I get to load the plug-in assembly.

One technique I've tried is:

var objType = Type.GetTypeFromProgID("My.ProgId");
var objLateBound = Activator.CreateInstance(objType);
IMyInterface netAssembly;
try
    {
    netAssembly = (IMyAssembly)objLateBound;
    }
catch (Exception)
    {
    netAssembly = null;
    }

If the cast to a .NET interface succeeds, the I know I have a .NET assembly and can access it through the interface. However, the technique is a bit clumsy and I'm getting problems with the COM side of things especially on 64-bit systems. I'd rather just eliminate loading the COM object and load the plug-in directly as a .NET assembly, if possible.

But the only piece of information I've got to go on is the plug-in's COM ProgID.

So, how can I go from a COM ProgID to loading a .NET Assembly, without creating any COM objects?

Answer 1

Look up in the registry to find the DLL associated with the ProgID you have. Once you have its full path, load it as a normal .NET assembly:

var type = Type.GetTypeFromProgID("My.ProgId", true);
var regPath = string.Format(@"{0}\CLSID\{1:B}\InProcServer32", 
    Registry.ClassesRoot, type.GUID);
var assemblyPath = Registry.GetValue(regPath, "", null);
if (!string.IsNullOrEmpty(assemblyPath))
{
    var assembly = Assembly.LoadFrom(assemblyPath);
    // Use it as a normal .NET assembly
}

Answer 2

Hi Tim,

may I ask how exactly, you're using the one .Net assembly within the other, via COM? That's my very problem- VS 2008 complains about the referenced tlb stemming from a .Net assembly...

thanks, steffen