Add COM-Visible Attributes

There are some cases when a company might want to convert some of its VB6 modules to .NET and keep using them in a COM environment. E.g.: convert the logic libraries and keep the front end in VB6. The “COM Visible” feature was implemented to assist in this scenarios.

When this optional feature is enabled, the VBUC will generate attributes for the COM-exposed classes and their members in order to keep the resulting assemblies exposed through a COM interface. This enables the resulting components to be called from other non-managed components via COM. A brief code sample:

Original VB6 Code:

The following method is declared in an ActiveX dll.

Public Sub method1()
    MsgBox    “Hello world”
End Sub

Resulting VB.NET Code:

Option Strict Off
Option Explicit On
Imports System
Imports System.Runtime.InteropServices
Imports System.Windows.Forms
<ComVisible(True)> _
<ProgId("Project1.Class1")> _
<ClassInterface(ClassInterfaceType.AutoDual)> _
Public Class Class1
    Public Sub method1()
        MessageBox.Show("hello world", Application.ProductName)
    
    End Sub    
End Class

Resulting C#.NET Code:

using System; 
using System.Runtime.InteropServices; 
using System.Windows.Forms; 
using VB6 = Microsoft.VisualBasic.Compatibility.VB6.Support; 

namespace Project1{

[ComVisible(true)][ProgId("Project1.Class1")][ClassInterface(ClassInterfaceType.AutoDual)]
public class Class1{

public void  method1(){
    MessageBox.Show("hello world", Application.ProductName);
}}
}