VB6 Types (Structs) with Fixed Length Strings

In VB6 the communication with backend services usually involves the definition of Types (or Structs) using fixed length strings.

VB6 provided language support for defining these data types. 

Public Type HostData     
	UserName       As String * 8
	PassWord       As String * 8
	FullName       As String * 50
End Type

struct HostData
    {
        [DebuggerDisplay("{s(UserName)}")]
        [MarshalAs(UnmanagedType.ByValArray, SizeConst=8)]
        public char[] UserName;

        [DebuggerDisplay("{s(PassWord)}")]
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 8)]
        char[] PassWord;

        [DebuggerDisplay("{s(FullName)}")]
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 50)]
        public char[] FullName;
        /// This method is used to provide a better display of
	 /// character arrays as strings on the debugger.
        string s(char[] array) { return new string(array); }

        public byte[] toByteArray() {    
           return StructsHelper.StructToByteArray(this);
        }

 public static explicit operator HostData(byte[] array)
        {
            return (HostData)StructsHelper.ByteArrayToStructure(array,typeof(HostData));
        }

        /// <summary>
        /// Constructor to initialize the char arrays that are used as fixed length strings
        /// Struct constructors must have at least one parameter.
        /// </summary>
        /// <param name="initFixedLengthStrings">if true will automatically init all fixed length char arrays according to the SizeConst property of the MarshalAs attribute</param>
        public HostData (bool initFixedLengthStrings=false)
        {
            UserName = null; 
            PassWord = null;
            FullName = null;
            if (initFixedLengthStrings)
            {
                StructsHelper.InitFixedStrings(GetType(), __makeref(this));
            }
        }
    }

[MarshalAs(UnmanagedType.ByValArray, SizeConst=n)]

[DebuggerDisplay("{s(<AttributeName>)}")]

public static void InitFixedStrings(Type type,TypedReference reference)  
        {
            if (type.IsValueType && !type.IsPrimitive && !type.Namespace.StartsWith("System") && !type.IsEnum)
            {//This should be an struct
                foreach (var field in
                    type.GetFields(System.Reflection.BindingFlags.Instance |
                    System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.NonPublic))
                {
                    
                    if (field.FieldType.IsArray && field.FieldType == typeof(char[]))
                    {
                        var attr = field.GetCustomAttributes(typeof(MarshalAsAttribute),false);
                        if (attr != null && attr.Length > 0)
                        {
                            MarshalAsAttribute maa = (MarshalAsAttribute)attr[0];
                            var constSize = maa.SizeConst;
                            if (constSize != -1)
                            {
                                var newValue = new char[constSize];
                                field.SetValueDirect(reference, newValue);
                            }
                        }
                    }
                }
            }
        }

/// <summary>
        /// Takes a bytearray and uses it to create a struct of the given type
        /// and populate it with the data of the byte array.
        /// NOTE: this method only works withs Structs which have a fixed size
        /// </summary>
        /// <param name="bytearray"> The data that will be used to initialize the struct</param>
        /// <param name="type">The type of the expected struct</param>
        /// <returns>A new struct instance with its fields initialized with the bytes from bytearray</returns>
        public static object ByteArrayToStructure(byte[] bytearray, Type type)
        {
            int len = Marshal.SizeOf(type);
            IntPtr i = Marshal.AllocHGlobal(len);
            Marshal.Copy(bytearray, 0, i, len);
            var obj = Marshal.PtrToStructure(i,type);
            Marshal.FreeHGlobal(i);
            return obj;
        }

/// <summary>
        /// Returns the contents of an struct as a byte array.
        /// It only works with fixed length structs.
        /// </summary>
        /// <param name="obj">the struct that holds the data that will be returned in the byte array</param>
        /// <returns>A byte array with the contents of the struct</returns>
        public static byte[] StructToByteArray(this object obj)
        {

            int len = Marshal.SizeOf(obj);
            byte[] arr = new byte[len];
            IntPtr ptr = Marshal.AllocHGlobal(len);
            Marshal.StructureToPtr(obj, ptr, true);
            Marshal.Copy(ptr, arr, 0, len);
            Marshal.FreeHGlobal(ptr);
            return arr;

        }

var hostData = new HostData (true);
var byteArray = UnicodeEncoding.Unicode.GetBytes(new String(' ', Marshal.SizeOf(typeof(HostData))));
hostData = (HostData)byteArray;

var size = Marshal.SizeOf(HostData);
var test = "helloworld";
test = test.PadRight(size, '*');
            
byteArray = UnicodeEncoding.Unicode.GetBytes(test);
hostData = (HostData)byteArray;

const string IF_VALUE_NOT_PROVIDED_THEN_RETURN_VALUE = "\0\0internal";
        /// <summary>
        /// This method is used to get/set the values of a char array as an string.
        /// It has been implemented in a way similar to that used in the jquery .val function.
        /// If called without parameters it will return the character array value as an string.
        /// If called with parameters will use the given string to set the character array value.
        /// If the given string is bigger that the character string the value is truncated
        /// </summary>
        /// <param name="array"></param>
        /// <param name="value"></param>
        /// <returns></returns>
        public static string val(this char[] array, String value = IF_VALUE_NOT_PROVIDED_THEN_RETURN_VALUE)
        {
            if (value == IF_VALUE_NOT_PROVIDED_THEN_RETURN_VALUE)
                return new string(array);
            else
            {
                var source = value.ToCharArray();
                Array.Copy(source, array, Math.Min(source.Length, array.Length));
                return value;
            }
        }

hostData.UserName.val(“Mauricio”)

String username = hostData.UserName.val();

StructsHelpers.cs (5.93 kb)

Share session state between ASP classic and ASP.NET or missing ASP classic and ASP.NET

Today my good friend Jafet asked me: "What do you think about sharing ASP classic and ASP.NET state?". And I told him that there were some projects for helping in this task.

I will mention some of them here.

The first one is NSession. This project provides an implementation that allows you to use the ASP.NET state server in ASP classic. You do not have to change your ASP classic code.

"You need to instantiate one of the COM objects in your ASP classic page before it accesses session state, either:

set oSession = Server.CreateObject("NSession.Session")

or

set oSession = Server.CreateObject("NSession.ReadOnlySession")

If you instantiate NSession.Session, the session state in the session store will be transferred to the ASP Classic session dictionary, and an exclusive lock will be placed in the session store. You do not need to change your existing code that accesses the ASP Classic session object. When NSession.Session goes out of scope, it will save the ASP Classic session dictionary back to the session store and release the exclusive lock.
If you have done with the session state, you can release the lock early with

set oSession = Nothing

If you instantiate NSession.ReadOnlySession, the session state in the session store will be transferred to the ASP Classic session dictionary but no locks will be placed."

The second option is SessionService. This project provides a mechanism for sharing the state between ASP classic and ASP.NET by serializing state data to an SQL Server.  The project page provides detailed information on how to setup IIS, how it is used in both platforms.

And the third option is a very interesting one called ASPClassicCompiler. This is a great great project. It provides a mechanism for compiling the ASP classic to .NET. This project is now opensource and we need to thank Li Chen for it.

Great ideas can be implemented thanks to this source. For example Brian Ellis suggested using the VBScript engine to replace the  MSScript.OCX. Another great one is an implementation of an View Engine that can be used with MVC and which support ASP Classic.

I really like the ASPClassic project and will be posting some interesting examples soon (as soon as I finish watching some Dr. Who episodes and the last Fringe season :) ) 

VB6 Interop of Function with Array of User Defined Type (UDT)

Well tonight while I was deleting some spam comments from my blog and watching Dr. Who with my wife, I found a rather interesting comment.

So the story was:

First there is a VB6 DLL that had a class called Class1 with code like the following:

public type emprecord 
name as string 
end type 

Public Sub Fn(T()as emprecord) 
 MsgBox "The silence is comming said Prisoner 0"
End Sub

When this little dll was called from a VB.NET big brother 

Dim test as new prj.class1   
Dim em(0) as prj.emprecord 'able to create it no problem 
em(0).name="hello" 
test.fn(em)  ' here gives error

An error ocurred... well this is not very document issue with the TLBIMP tool which creates the interop assemblies. See StackOverflow Answer. The workaround is to right click on your type library, select properties, and change Embed interop Types to false.

After that you will be able to call your function.

Simplify app deployment in .NET

Office Interop and Call was rejected by callee

This issue is mostly cause by timing issues when calling a multi-threaded app.

Some workarounds:

1. Set the application visible property to false. For example if using Word make word visible property false at the start of the method and set it back to true at the end.

This will delay some GUI changes avoiding timing issues.

2. Insert some Thread.Sleep calls (yes this is ugly)

3. Register and IOleMessageFilter. I have copied an implementation from the MSDN

Just copy this class in your code.

At the start of the method call 

            MessageFilter.Register();
            // This registers the IOleMessageFilter to handle any threading 
            // errors.

And at the end

MessageFilter.Revoke();

public class MessageFilter : IOleMessageFilter
{

        //
        // Class containing the IOleMessageFilter
        // thread error-handling functions.

        // Start the filter.
        public static void Register()
        {
            IOleMessageFilter newFilter = new MessageFilter(); 
            IOleMessageFilter oldFilter = null; 
            CoRegisterMessageFilter(newFilter, out oldFilter);
        }


        // Done with the filter, close it.
        public static void Revoke()
        {
            IOleMessageFilter oldFilter = null; 
            CoRegisterMessageFilter(null, out oldFilter);
        }


        //
        // IOleMessageFilter functions.
        // Handle incoming thread requests.
        int IOleMessageFilter.HandleInComingCall(int dwCallType, 
        System.IntPtr hTaskCaller, int dwTickCount, System.IntPtr lpInterfaceInfo) 
        {

            //Return the flag SERVERCALL_ISHANDLED.
            return 0;
        }


        // Thread call was rejected, so try again.
        int IOleMessageFilter.RetryRejectedCall(System.IntPtr 
        hTaskCallee, int dwTickCount, int dwRejectType)
        {

            if (dwRejectType == 2)
            // flag = SERVERCALL_RETRYLATER.
            {
                // Retry the thread call immediately if return >=0 & 
                // <100.
                return 99;
            }
            // Too busy; cancel call.
            return -1;
        }


        int IOleMessageFilter.MessagePending(System.IntPtr hTaskCallee, 
        int dwTickCount, int dwPendingType)
        {
            //Return the flag PENDINGMSG_WAITDEFPROCESS.
            return 2; 
        }


        // Implement the IOleMessageFilter interface.
        [DllImport("Ole32.dll")]
        private static extern int 
          CoRegisterMessageFilter(IOleMessageFilter newFilter, out 
          IOleMessageFilter oldFilter);
    }



    [ComImport(), Guid("00000016-0000-0000-C000-000000000046"), 
    InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)]
    interface IOleMessageFilter 
    {
        [PreserveSig]
        int HandleInComingCall( 
        int dwCallType, 
        IntPtr hTaskCaller, 
        int dwTickCount, 
        IntPtr lpInterfaceInfo);

        [PreserveSig]
        int RetryRejectedCall( 
        IntPtr hTaskCallee, 
        int dwTickCount,
        int dwRejectType);


        [PreserveSig]
        int MessagePending( 
            IntPtr hTaskCallee, 
            int dwTickCount,
            int dwPendingType);
    }

STAThread and Memory Issues

VB6 Application where STAThread. And that is the reason that Winforms applications are
by default STAThread. Using MTAThread causes problems with some ActiveX Controls.

However STAThread has a nasty implication
see: http://social.msdn.microsoft.com/Forums/en/clr/thread/835db88e-db51-4f83-bd4f-a10d126effa6
 
"inside a STA thread, the finalizer thread must reenter the STA thread in order to finalize the component.
If the STA is blocked and isn't pumping, the finalizer has to wait in line until it does"

This can then cause leaks of components affecting the memory use.

"To get around this issue, you have some options (from best to worst), e.g.:"

1) Create your components in an MTA. ... Unless you have an explicit reason to use an STA, you shouldn't. I realize that Visual Studio adds these to some entrypoints automatically for you.
For example, most GUI applications have to start life inside an STA, e.g. WinForms, but Console applications"  or services "certainly do not."

"2) Deterministically release your resources. If you are using components which implement IDisposable, wrap them in
a C# 'using' statement or call Dispose() on them explicitly when you're done.
RCW's done have Dispose on them. You can consider doing a Marshal.ReleaseComObject on them directly,
but realize that this can cause problems if you're not really done using the COM object."

"3) Use another form of blocking to prevent the primary thread from exiting."

"Chris Brumme writes about this" (COM Apartments)
" at http://blogs.msdn.com/cbrumme/archive/2004/02/02/66219.aspx; caution: that's a fairly lengthy post"

Add Return for COM Interop marshaling to Short in Vb.NET

In VB.NET if you want to make your interfaces available thru COM and make sure that its parameters are of a certain type you have to use the MarshalAs attribute. For the return type it is a little tricky because it has to be added after the As Keyword.

<ComVisible(True)> _
<Guid("15D492C7-CD14-4239-B98D-689F329EEDA4")>
<InterfaceType(ComInterfaceType.InterfaceIsDual)> _
Public Interface MyCOMInterface
	Function FooReturningShort(ByVal data As Integer, <MarshalAs(UnmanagedType.U2)> ByVal shortData As short) As <MarshalAsAttribute(UnmanagedType.U2)> Short
End Interface

How to add helpstring in tlb generate from VB.NET or C# class

In IDL you can have a helpstring attribute that adds descriptions to your interfaces.
To be able to generated those helpstring tags in a VB.NET  class you should use the Description tag

For example see this example taken from:http://stackoverflow.com/questions/6668500/getting-the-helpstring-attribute-applied-to-c-sharp-properties-exposed-via-com-i

using System;
using System.ComponentModel;
using System.Runtime.InteropServices;



namespace ClassLibrary1 {
    [ComVisible(true), InterfaceType(ComInterfaceType.InterfaceIsDual)]
    public interface IFoo {
        int property {
            [Description("prop")]
            get;
            [Description("prop")]
            set;
        }
    }
}

NOTE: remenber that in some cases you have to apply the description attribute to both get and set.

ADITIONAL NODE:

After some test, I found that there are some differences with the helpstring behaviour in VB.NET. For example the helpstring attribute is not generated for methods. More on C#/VB.NET Interop Differences http://mheironimus.blogspot.com/2006/10/vbnet-com-interface-issues.html

Interop Structures to UnManaged Dlls

For VB6 applications it is common to rely on OS or Kernel API Calls. Some of those APIs might
need you to send data back and for the native API.

Marshalling in .NET can be complicated and bothersome. I have published several posts about
interop. But it usually depends on adding several marshalling attributes and even tricks specially for
fixed strings.

So I decided to provide a more a simpler approach for conversion. In this approach you just need to things:

1. Your VB6 types or structs will be mapped to .NET classes
2. All VB6 type or struct fields will be mapped to public fields
3. An attribute must be used on those fields to indicate the field length, for arrays or strings.
4. Extension methods .AsString() .SetFromString and .GetClassLength will handle all the complexities of setting the struct fields.

Let’s see an example:

Type EmployeeRecord
    FirstName As String * 5
    LastName As String * 5
End Type

That vb6 type will be mapped in .NET following this approach to:

    public class EmployeeRecord 
    {
        [FixedLength(5)]
        public string FirstName = "Mau";
        [FixedLength(5)]
        public string LastName = "Rojas";

    }

You can then simple use that class in .NET

var emp = new EmployeeRecord {FirstName="Mauricio",LastName="Rojas"} ;
var str = emp.AsString();
//This str value will be "MauriRojas" the helper extension methods
// .AsString and .SetFromString will handle setting the internal class fields

All that is very good but how is this used in Marshalling?? Well very simple. Let’s say you have a Dll called foo.dll
with a function foo that receives an EmployeeRecord:

        [DllImport("foo.dll")]
        public static extern int foo(IntPtr Struct);

Then if you want to call that function you will do something like:

            var emp = new EmployeeRecord { FirstName="Ann",LastName="Smith"};
            string str = emp.AsString();
            var ptr = IntPtr.Zero;
            ptr = Marshal.StringToBSTR(str);
            //or 
            ptr = Marshal.StringToHGlobalAnsi(str);
            //or
            ptr = Marshal.StringToHGlobalAuto(str);
            //or
            ptr = Marshal.StringToHGlobalUni(str);

            //And call the native function
            foo(ptr);

If the function modifies the structure and you want to reflect those changes then you will do something like:

str = Marshal.PtrToStringAnsi(ptr,typeof(EmployeeRecord).GetClassLength())
emp.SetFromString(str);

This solution can also be applied for more complex structures. For example:

    public class EmployeeRecord 
    {
        [FixedLength(5)]
        public string FirstName = "Mau";
        [FixedLength(5)]
        public string LastName = "Rojas";

    }

    public class Record1
    {
        public int field1;
        [FixedLength(10)]
        public string field2 = "";
        public EmployeeRecord rec = new EmployeeRecord();
    }

    public class GeneralInfo
    {
        public int field1;
        [ArrayLength(5)]
        [FixedLength(2)]
        public String[] countrycodes = { "cr","es","mx","pa","ni"};
        [FixedLength(2)]
        public EmployeeRecord[] employees;
    }

If you want to try it out this is the link to the CODE

Interop: BinaryCompatibilty for VB6 Migrations

In VB6 when you have an ActiveX Library it was very important to use
the BinaryCompatibility setting to make sure that your applications did not break after a change.

So let’s first introduce what is binary compatibility and how to accomplish that in .NET.

Binary Compatibility allows to make changes to your components or COM classes without recompiling
every application you've made that uses the component.
And why do you need it. Why compatibility breaks.
On lets see.

An ActiveX Control or DLL expose Public interfaces.
Those interfaces have all of the properties, methods, events, etc. that you've marked as Public.
In other words, everything you've added that shows in Intellisense while working outside of your component.

Now let's say you have create a class, with two Methods Method1 and Method2

When you compile, VB generates all the COM infraestructure you need for your component.
It defines a CoClass and an interface and an entry for each method.

For a vb class with two methods:

Sub Method1()

End Sub

Sub Method2()

End Sub

It will produce a typelib like:

// Generated .IDL file (by the OLE/COM Object Viewer)
// 
// typelib filename: <could not determine filename>
[
  uuid(8ABA2C0C-7CCA-40CD-A944-56707566634A),
  version(1.0)
]
library Project1
{
    // TLib :     // TLib : OLE Automation : {00020430-0000-0000-C000-000000000046}
    importlib("stdole2.tlb");

    // Forward declare all types defined in this typelib
    interface _Class1;

    [
      odl,
      uuid(6B86684C-B3DD-4680-BF95-8DEE2C17AF5B),
      version(1.0),
      hidden,
      dual,
      nonextensible,
      oleautomation
    ]
    interface _Class1 : IDispatch {
        [id(0x60030000)]
        HRESULT Method1();
        [id(0x60030001)]
        HRESULT Method2();
    };

    [
      uuid(C71C7AB0-552A-4D5D-A9FB-AF33830A697E),
      version(1.0)
    ]
    coclass Class1 {
        [default] interface _Class1;
    };
};

As you can see in the typelib there are IDs associated to each coclass, interface and
methods. Those IDs are the ones use when you generate the .exe file for your application.
Now if you modify your Class to:

Sub Method3()

End Sub

Sub Method4()

End Sub

Sub Method1()

End Sub

Sub Method2()

End Sub

and you use No Compatibility the typelib after your changes will be:

// Generated .IDL file (by the OLE/COM Object Viewer)
// 
// typelib filename: <could not determine filename>

[
  uuid(FE5C56C2-E03A-4DC0-994D-B68543C72A46),
  version(1.0)
]
library Project1
{
    // TLib :     // TLib : OLE Automation : {00020430-0000-0000-C000-000000000046}
    importlib("stdole2.tlb");

    // Forward declare all types defined in this typelib
    interface _Class1;

    [
      odl,
      uuid(A3032E1E-52FE-42E0-98FF-84A9DD4FD8C3),
      version(1.0),
      hidden,
      dual,
      nonextensible,
      oleautomation
    ]
    interface _Class1 : IDispatch {
        [id(0x60030000)]
        HRESULT Method3();
        [id(0x60030001)]
        HRESULT Method4();
        [id(0x60030002)]
        HRESULT Method1();
        [id(0x60030003)]
        HRESULT Method2();
    };

    [
      uuid(72721504-CC56-4BB9-9447-C7193FE8C02D),
      version(1.0)
    ]
    coclass Class1 {
        [default] interface _Class1;
    };
};

As you can see, now the ids for the methods, CoClass are different, so your applications will return errors like: Error 430 (Automation error, the component dies horribly) or Error 429 (can't create the object at all)

But if you instead used BinaryCompatibility then the typelib for your class will be:

// Generated .IDL file (by the OLE/COM Object Viewer)
// 
// typelib filename: <could not determine filename>
[
  uuid(8ABA2C0C-7CCA-40CD-A944-56707566634A),
  version(1.1)
]
library Project1
{
    // TLib :     // TLib : OLE Automation : {00020430-0000-0000-C000-000000000046}
    importlib("stdole2.tlb");

    // Forward declare all types defined in this typelib
    interface _Class1;
    [
      odl,
      uuid(6E9C59C3-82D7-444C-92FB-01B49D91A2FF),
      version(1.1),
      hidden,
      dual,
      nonextensible,
      oleautomation
    ]
    interface _Class1 : IDispatch {
        [id(0x60030002)]
        HRESULT Method3();
        [id(0x60030003)]
        HRESULT Method4();
        [id(0x60030000)]
        HRESULT Method1();
        [id(0x60030001)]
        HRESULT Method2();
    };

    [
      uuid(C71C7AB0-552A-4D5D-A9FB-AF33830A697E),
      version(1.1)
    ]
    coclass Class1 {
        [default] interface _Class1;
    };

    typedef [uuid(6B86684C-B3DD-4680-BF95-8DEE2C17AF5B), version(1.0), public]
    _Class1 Class1___v0;
};

If you compare now the two typelibs you can see the Method1 and Method2 keep the same ids.

For each version a typedef is generated that will point to the last version. For example adding a Method5 will add new entry like:

    typedef [uuid(6B86684C-B3DD-4680-BF95-8DEE2C17AF5B), version(1.0), public]
    _Class1 Class1___v0;

    typedef [uuid(6E9C59C3-82D7-444C-92FB-01B49D91A2FF), version(1.1), public]
    _Class1 Class1___v1;

Well that is what binary compatibility does. Now how to achieve binary compatibility in .NET

Binary Compatibility in .NET

Achieving binary compatibility in .NET is really easy. You just need to give more information to
make explicit how your typelib information will be. I will follow an approach as the one I already explained in this post:
http://blogs.artinsoft.net/mrojas/archive/2010/06/23/exposing-c-classes-thru-interop.aspx

Lets take our previous example:

using System;
using System.Runtime.InteropServices;

namespace InteropExamples
{
    public class Class1
    {
        public void Method3()
        {
        }
        public void Method4()
        {
        }
        public void Method1()
        {
        }
        public void Method2()
        {
        }
        public void Method5()
        {
        }
    }
}

In previous posts I had recommended using partial classes and using interfaces to explicitly specify what you what to be seen in COM. This means you start up with something like:

  public partial class Class1
    {
        public void Method3()
        {
        }
        public void Method4()
        {
        }
        public void Method1()
        {
        }
        public void Method2()
        {
        }
    }

    [ComVisible(true)]
    public interface _Class1
    {
        void Method3();
        void Method4();
        void Method1();
        void Method2();

    }
    [ComVisible(true)]
    [ClassInterface(ClassInterfaceType.None)]
    [ComDefaultInterface(typeof(_Class1))]
    partial class Class1 : _Class1
    {
        #region _Class1 Members

        void _Class1.Method3()
        {
            Method3();
        }

        void _Class1.Method4()
        {
            Method4();
        }

        void _Class1.Method1()
        {
            Method1();
        }

        void _Class1.Method2()
        {
            Method2();
        }

        #endregion
    }

Now to make this code binary compatible then you have to make sure that the tlb file generated for your class is almost identical to that generated before. To acomplish that we must make sure that we your methods, interfaces and classes have the same guids and ids. Lets see how:

using System;
using System.Runtime.InteropServices;

namespace InteropExamples
{
    public partial class Class1
    {

        public void Method3()
        {
            System.Windows.Forms.MessageBox.Show("3 N");
        }

        public void Method4()
        {
            System.Windows.Forms.MessageBox.Show("4 N");
        }

        public void Method5()
        {
            System.Windows.Forms.MessageBox.Show("5 N");
        }


        public void Method1()
        {
            System.Windows.Forms.MessageBox.Show("1 N");
        }

        public void Method2()
        {
            System.Windows.Forms.MessageBox.Show("2 N");
        }
    }

    [ComVisible(true)] //This to make the interface Visible for COM
    [TypeLibType((TypeLibTypeFlags)((short)TypeLibTypeFlags.FHidden |
        (short)TypeLibTypeFlags.FDual |
        (short)TypeLibTypeFlags.FNonExtensible |
        (short)TypeLibTypeFlags.FOleAutomation))] //This to use the same flags as in previous tlb
    [Guid("9BAFD76D-8E6B-439C-8B6D-37260BFA3317")] //This is to make the class have the guid
    public interface _Class1
    {
        [DispId(0x60030000)]
        void Method1();
        [DispId(0x60030001)]
        void Method2();
        [DispId(0x60030002)]
        void Method3();
        [DispId(0x60030003)]
        void Method4();
        [DispId(0x60030004)]
        void Method5();


    }

    [ComVisible(true)] //This to make the class Visible for COM
    [ClassInterface(ClassInterfaceType.None)] //This is to make sure that we have control on interface generation
    [ComDefaultInterface(typeof(_Class1))] //To set default interface
    [ProgId("Project1.Class1")] //To set ProgId 
    [Guid("C71C7AB0-552A-4D5D-A9FB-AF33830A697E")] //Maintain same Guid.
    partial class Class1 : _Class1, Class1___v0, Class1___v1
    {
        #region _Class1 Members

        void _Class1.Method3()
        {
            Method3();
        }

        void _Class1.Method4()
        {
            Method4();
        }

        void _Class1.Method1()
        {
            Method1();
        }

        void _Class1.Method2()
        {
            Method2();
        }

        #endregion


        #region Class1___v0 Members

        void Class1___v0.Method1()
        {
            Method1();
        }

        void Class1___v0.Method2()
        {
            Method2();
        }

        void Class1___v0.Method3()
        {
            Method3();
        }

        void Class1___v0.Method4()
        {
            Method4();
        }

        void Class1___v0.Method5()
        {
            Method5();
        }

        #endregion

        #region Class1___v1 Members

        void Class1___v1.Method1()
        {
            Method1();
        }

        void Class1___v1.Method2()
        {
            Method2();
        }

        void Class1___v1.Method3()
        {
            Method3();
        }

        void Class1___v1.Method4()
        {
            Method4();
        }

        void Class1___v1.Method5()
        {
            Method5();
        }

        #endregion
    }

    //This is to keep compatibility with old versions
    //we cannot generate a typedef so we will need to add all of the versions
    //for BinaryCompatibility
    [ComVisible(true)]
    [Guid("6B86684C-B3DD-4680-BF95-8DEE2C17AF5B")]
    [TypeLibType(TypeLibTypeFlags.FHidden)]
    public interface Class1___v0
    {
        [DispId(0x60030000)]
        void Method1();
        [DispId(0x60030001)]
        void Method2();
        [DispId(0x60030002)]
        void Method3();
        [DispId(0x60030003)]
        void Method4();
        [DispId(0x60030004)]
        void Method5();
    }

    //This is to keep compatibility with old versions
    //we cannot generate a typedef so we will need to add all of the versions
    //for BinaryCompatibility
    [ComVisible(true)]
    [Guid("4A7A3317-BF13-443E-9DB0-2C5EA21F00CA")]
    [TypeLibType(TypeLibTypeFlags.FHidden)]
    public interface Class1___v1
    {
        [DispId(0x60030000)]
        void Method1();
        [DispId(0x60030001)]
        void Method2();
        [DispId(0x60030002)]
        void Method3();
        [DispId(0x60030003)]
        void Method4();
        [DispId(0x60030004)]
        void Method5();
    }

}

Sadly in .NET you cannot use Interface Inheritance in COM. If there is interface inheritance YOU HAVE TO IMPLEMENT each interface. In the case of code that comes from VB6. VB6 just uses typedefs, so you really don’t know which methods belong to each version. So in the end all versions have all methods.

The other alternative to this method, is just to implement last version. And after generating the tlb, decompile it to an .IDL file add the typedefs and recompiled it. I explained something similar in this post:http://blogs.artinsoft.net/mrojas/archive/2010/05/17/interop-remove-prefix-from-c-enums-for-com.aspx

Ok. I hope this helps you to have an more clear idea of what Binary Compatibility is and how to do it in .NET. I am attaching some sample code. It show an ActiveX library that uses BinaryCompatibility and three version on an aplications that uses the different versions. And also a .NET class library that is equivalent to the VB6 one. HERE

Enjoy.