Making COM Object For ASP.NET Use

bluethecow · #1 (**permalink**) September 27th, 2006, 09:17 PM

Not sure if this is the right board, but here it goes.

I'm trying to learn how to create a COM object in a C++ DLL, register it properly, and then use it in a .aspx page.

My [desired] usage is this: (custom math class and add function used for simplicity to learn):

Code:

<%@ Page Language="VB" Debug="true" aspcompat="true" %>
<script language="vb" runat="server">
Sub Page_Load(sender as Object, e as EventArgs)
 Dim oMath=Server.CreateObject("MathX.CCalculator.1")
 Dim c=0
 oMath.Add(1,2,c) 'c should be 1+2=3
 Response.Write(c)
 Response.End()
End Sub
</script>

Then I created and registered the DLL, but when I run the aspx page I get this error:
"System.NullReferenceException: Object reference not set to an instance of an object."
It is referring to the oMath object being null. So, now I'm not sure what I need to add to my DLL to make this work... I have the 4 COM functions created and then exported like such in the DEF file:

Code:

EXPORTS
    DllCanUnloadNow        PRIVATE
    DllGetClassObject    PRIVATE
    DllRegisterServer    PRIVATE
    DllUnregisterServer    PRIVATE

And I have an ICalculator interface, a CCalculator object class, and a CFCalculator class factory implemented.

Can someone point me in the right direction? Or where to look? I'm not even sure where the problem would be. I can give specific code of the C++ DLL if necessary.

bluethecow · #2 (**permalink**) September 30th, 2006, 10:06 PM

I think the problem lies somewhere in the Server.CreateObject() method call. When I looked it up on MSDN, it said that it creates an instance of a registered component (so that IIS can access it?), so I figure my problem is either is related to not creating the object correctly in the DLL, or to not registering the object correctly.

I'm thinking the second is more likely (and I'm hopeful that it is the second one, as it would be easier to figure out how to fix), and so I need to know if I'm registering it right.
So far, all I'm doing to register it is adding the following to the registry:

Code:

HKEY_CLASSES_ROOT\CLSID\{...} ("...", replace with UUID) 
  default value: "Simple COM Test Class"
{...}\InProcServer32
  default value: [filepath]
  ThreadingModel: "Apartment"
{...}\ProgId
  default value: "MathX.CCalculator.1"

HKEY_CLASSES_ROOT\MathX.CCalculator.1
  no default value
MathX.CCalculator.1\CLSID
  default value: {...} (UUID again)

So basically its a bunch of referencing- the prog id gives the UUID which gives the prog id and the filepath of DLL. Do I need anything else?

Need to download code?

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