Ineed to pass a window handle (long) from VB6 client to a library written in VB.Net for some processing (using interop). I don't know how to make use of the hwnd from VB6 and get the correct window handle in .Net.

Please help!

btw, Im on VS 2008 SP1 and .Net framework 3.5 SP1

I should have checked for a unicode version of the API function call (MessageBoxIndirectW) which can be called directly from a VB 6.0 app.

http://www.vbforums.com/showthread.php?t=541220

VB.Net 

Imports System.Windows.Forms

<ComClass(CTest.ClassId, CTest.InterfaceId, CTest.EventsId)> _
Public Class CTest

#Region "COM GUIDs"
    ' These  GUIDs provide the COM identity for this class 
    ' and its COM interfaces. If you change them, existing 
    ' clients will no longer be able to access the class.
    Public Const ClassId As String = "75bce494-cfa8-46fd-8f2e-550aee2ebd47"
    Public Const InterfaceId As String = "8c003cc9-e226-4f9e-87c4-54619a2b9482"
    Public Const EventsId As String = "bbbf2e72-74f9-4514-8970-5a73ec62d421"
#End Region

    ' A creatable COM class must have a Public Sub New() 
    ' with no parameters, otherwise, the class will not be 
    ' registered in the COM registry and cannot be created 
    ' via CreateObject.
    Public Sub New()
        MyBase.New()
    End Sub

    Public Shadows Function MessageBoxU(ByVal Prompt As String, Optional ByVal Title As String = "", Optional ByVal OwnerHandle As Integer = 0) As Integer
        Try
            Dim iPtr As IntPtr
            Dim oWindWrapper As CWindowWrapper

            If OwnerHandle > 0 Then
                iPtr = New IntPtr(OwnerHandle)
                oWindWrapper = New CWindowWrapper(iPtr)


                Return MessageBox.Show(oWindWrapper, Prompt, Title)
            Else
                Return MessageBox.Show(Prompt, Title)
            End If

        Catch

        End Try


    End Function

End Class

Imports System.Windows.Forms

Class CWindowWrapper
    Implements IWin32Window

    Private _hwnd As IntPtr

    Public Sub New(ByVal handle As IntPtr)
        _hwnd = handle
    End Sub

    Public ReadOnly Property Handle() As IntPtr Implements IWin32Window.Handle
        Get
            Return _hwnd
        End Get
    End Property

End Class

-----------------------------------------------------------------
VB6 Client Code
On a form add these three controls
TextBox, CheckBox and Command Button
 and paste the following code

Option Explicit

Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long

Private Declare Function MessageBox Lib "user32" Alias "MessageBoxA" _
(ByVal hWnd As Long, ByVal lpText As String, ByVal lpCaption As String, ByVal wType As Long) As Long


Private Sub Command1_Click()
    Dim ot As New CTest
    Dim Whdl As Long
    
    'Text1.Text is any Window Caption
    Whdl = FindWindow(vbNullString, Text1.Text)
       
    If Check1.Value = vbChecked Then
        'use Win32 API
        MessageBox Whdl, "Hello on Window (" & Text1.Text & ")", "My Caption", vbInformation
    Else
        'use .Net MessageBox
        If Whdl > 0 Then
            ot.MessageBoxU "Hello on Window (" & Text1.Text & ")", "My Caption", Whdl
        Else
            ot.MessageBoxU "Window Not Found (" & Text1.Text & ")", "My Caption"
        End If
    End If
End Sub

Example code converted to VB:

   MessageBox.Show(New WindowWrapper(hwnd), "Hello World!")

   Public Class WindowWrapper
        Implements System.Windows.Forms.IWin32Window
        Public Sub New(ByVal handle As IntPtr)
            _hwnd = handle
        End Sub

        Public ReadOnly Property Handle() As IntPtr Implements System.Windows.Forms.IWin32Window.Handle
            Get
                Return _hwnd
            End Get
        End Property

        Private _hwnd As IntPtr
    End Class

Public Shadows Function MessageBoxU(ByVal Prompt As String, Optional ByVal Title As String = "", Optional ByVal OwnerHandle As Integer = 0) As Integer

Dim iPtr As IntPtr

New IntPtr(OwnerHandle)

MessageBox.Show(

New CWindowWrapper(iPtr), Prompt, Title)

End Function

Declare Function FindWindow Lib "user32.dll" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Integer

New WindowWrapper(New IntPtr(handle)), "My Message: " & TextBox1.Text, "My Caption - " & TextBox1.Text)

'MessageBox(handle, "My Message: " & TextBox1.Text, "My Caption - " & TextBox1.Text, vbInformation)

End Sub

I should have checked for a unicode version of the API function call (MessageBoxIndirectW) which can be called directly from a VB 6.0 app.

http://www.vbforums.com/showthread.php?t=541220

Riquel
This worked! Thank you so much for your help. The solution Paul gave below is also good and works for me. Now I have a choice!

Thank you for your help, I appreciate it very much.

Narsi

Paul
This worked! Thank you so much for your help.Riquel's solution above is also works. Now I have a choice!

Thank you for your help, I appreciate it very much.

Narsi