Create COM object using C# for VB6 Application

Here is a C# example: Create a COM object with events using C# and implement in a VB6 Application.

Step #1: Define COM interfaces
Need to create two interfaces - 1 class interface and a events interface

Public Class Interface: IMyClass

using System;
using System.Drawing;
using PicasaBloggerUserControls;
using System.Runtime.InteropServices;

namespace MyApp
{
[Guid("xxxxxxxx-yyyy-zzzz-aaaa-bbbbbbbbbbbb")]
[InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
public interface IMyClass
    {
   void GetDRCUpdate(string url, int majorVer, int minorVer, int RevisionVer, bool GetLatest);
}
}

Public Interface defining the events: IMyClassEvents

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

namespace MyApp
{
[InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
[Guid("xxxxxxxx-yyyy-zzzz-aaaa-bbbbbbbbbbbb")]
public interface IMyClassEvents
    {
    void DownloadComplete();
    void DownloadCancel(bool downloadfailed);
}
}

Step #2
Define Public class using class interface: winformUI

using System.Drawing;
using System.Windows.Forms;
using PicasaBloggerUserControls;
using System.Runtime.InteropServices;

namespace PicasaBloggerUI
{
 [Guid("xxxxxxxx-yyyy-zzzz-aaaa-bbbbbbbbbbbb")]
 [
  ComSourceInterfaces("MyApp.PicasaBloggerEventsInterface"),
  ClassInterface(ClassInterfaceType.None)
 ]
 [ProgId("winformUI")]


 public class winformUI : IMyClass
 {
     public event FileDownloadDelegate DRCDownloadComplete;
     public delegate void FileDownloadDelegate();

     public event FileDownloadCancelDelegate DRCDownloadCancel;
     public delegate void FileDownloadCancelDelegate(bool downloadfailed); 

     private frmDRCUpdate _DRCUpdater;     
 
     //ctor
     public winformUI()
     {         
         _DRCUpdater = new frmDRCUpdate();
         _DRCUpdater.OnFileDownload += new frmDRCUpdate.FileDownloadDelegate(_DRCUpdater_OnFileDownload);
         _DRCUpdater.OnFileDownloadCancel += new frmDRCUpdate.FileDownloadCancelDelegate(_DRCUpdater_OnFileDownloadCancel);
     }

     void _DRCUpdater_OnFileDownloadCancel()
     {
         if (null != DRCDownloadCancel)
         {
             DRCDownloadCancel(!_DRCUpdater.Successful);
         }
     }

     void _DRCUpdater_OnFileDownload()
     {
         try
         {
             //MessageBox.Show("Download Successful");
             DRCDownloadComplete();
         }
         catch
         {
         }
     
     }             

     void IPicasaBlogger.GetDRCUpdate(string url, int majorVer, int minorVer, int RevisionVer, bool GetLatest)
     {
         _DRCUpdater = new frmDRCUpdate();
         _DRCUpdater.OnFileDownload += new frmDRCUpdate.FileDownloadDelegate(_DRCUpdater_OnFileDownload);
         _DRCUpdater.OnFileDownloadCancel += new frmDRCUpdate.FileDownloadCancelDelegate(_DRCUpdater_OnFileDownloadCancel);
         _DRCUpdater.Show();
         _DRCUpdater.GetDRCUpdate(url, majorVer, minorVer, RevisionVer, GetLatest);       
     }

 }
}

Step #3 Compile C# code and register the assembly:

REGASM MyApp.dll /tlb:com.MyApp.tlb

Now you are ready to add the COM object as a reference to a VB project.
1) Open VB6 project, select references and browse to locate of MyApp.tlb and add as a reference.

In a VB6 form Module

Private WithEvents oMyAppUI As MyApp.winformUI

Private Sub Form_Load()
   Set oMyAppUI = New MyApp.winformUI
End Sub

Private Sub oMyAppUI_DownloadCancel(ByVal downloadfailed As Boolean)
  If downloadfailed Then
      MsgBox "Update Failed, please try again.  If the failure persists, contact me at Gary.Kindel@gmail.com for assistance.", vbOKOnly
  Else
      MsgBox "You have the current version, no updates are available.", vbExclamation
  End If
End Sub
Private Sub oMyAppUI_DownloadComplete()
   If MsgBox("Do you want to exit and install the update?", vbYesNoCancel, "Exit DRC and run Update file") = vbYes Then
       mApplyUpdate = True
       Unload Me
   End If
End Sub