Programming VB.Net dll's for use with COM?

[Joacim Andersson]

There is, as you've probably noticed, a number of approaches that are presented in the documentation as optional.
The following is a short description, or presentation, that showing you the correct way to expose VB.Net objects but it's limited to that without all the optional approaches.

The easiest way is to simply check the "Register for COM interop" checkbox on the project setting dialog box.
However, as you have noticed, doing so will only support late binding.
VB.Net will not automatically create the private dual interface fir a class that allows both early and late binding, you'll just have to do that yourself.
So the correct way is to write the interface and explicitly define it in the Class.

Imports System.Runtime.InteropServices
Public Interface _CallableFromCOM
    Function SomeMethod(ByVal i As Integer) As Integer
    '... all other methods
End Interface
 
Public Class CallableFromCOM
    Implements _CallableFromCOM 'implement the interface
    Public Function SomeMethod(ByVal i As Integer) As Integer Implements _CallableFromCOM.SomeMethod
        Return i
    End Function
End Class

Now, you have to instruct the VB.Net compiler that COM objects can use this component.
This is accomplished by setting the ComVisible attribute for the assembly (in the AssemblyInfo.vb file)

<Assembly: ComVisible(True)>
<Assembly: ClassInterface(ClassInterfaceType.None)>

You can, and should, also set the AssemblyDescription attribute to some value because this will appear in the Project Reference dialog box in VB 6.

<Assembly: AssemblyDescription("Type in some description here")>

Best regards