Question

I have a C# class library project (dll) with a single class, COMTest:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;

namespace COMTest
{
    [Guid("45D639E4-FDDE-4b7b-A35F-FC19856DFF24")]
    [ComVisible(true)]
    public class Foo
    {
        public Foo()
        {
            Console.WriteLine("Constructing Foo");
        }

        private string mName = "FOO";
        public string Name
        {
            get { return mName; }
            set { mName = value; }
        }
    }
}

The project is registered for COM interop, and the assembly is COM-visible. The target framework is .Net 3.5, and the platform target is x86. The .dll is registered using the 32-bit C:\Windows\Microsoft.NET\Framework\v2.0.50727\RegAsm.exe /codebase COMTest.dll

I am attempting to access this class from VBScript (again, 32-bit, using C:\Windows\SysWOW64\cscript.exe test.vbs), but I appear to be having problems acquiring an instance of Foo within the script. I can use the class; I just can’t keep any reference to it.

Here is my script:

Wscript.Echo "CreateObject(""ComTest.Foo"").Name Results: " + CreateObject("COMTest.Foo").Name
IF IsEmpty(CreateObject("COMTest.Foo")) THEN Wscript.Echo "CreateObject() is empty" ELSE Wscript.Echo "CreateObject() is NOT empty"

DIM foo : CreateObject("COMTest.Foo")
IF IsEmpty(foo) THEN Wscript.Echo "foo is empty" ELSE Wscript.Echo "foo is NOT empty"

And here is the output:

Constructing Foo
CreateObject("ComTest.Foo").Name Results: FOO
Constructing Foo
CreateObject() is NOT empty
Constructing Foo
foo is empty

As you can see, the CreateObject() call succeeds–I’m just unable to keep a reference to the object returned (in foo).

I feel like I’m missing something simple. How do I retain the object returned from CreateObject()?

Answer 1

The colon you use in line three doesn’t actually do anything, it just separates two different statements. Your Dim foo : CreateObject("COMTest.Foo") is equivalent to:

Dim foo
CreateObject("COMTest.Foo")

Which creates the object but doesn’t actually set its reference to any variable. I would write it like this:

Dim foo
Set foo = CreateObject("COMTest.Foo")
WScript.Echo foo.Name