Private Function InternSendData(Data As String, hWnd As Long) As Boolean
    On Error GoTo Fehler
    Dim DesthWnd As Long, B() As Byte
    Dim CD As COPYDATASTRUCT
    Dim lRet As Long
 
    DesthWnd = hWnd
    If DesthWnd = 0 Then
        InternSendData = False
    Else
        CD.dwData = 1
        B = StrConv(Data, vbFromUnicode)
        CD.cbData = Len(Data) + 1
        CD.lpData = VarPtr(B(0))
 
        DoEvents
        lRet = PostMessage(DesthWnd, WM_COPYDATA, 0, CD)
        InternSendData = True
    End If
    Exit Function
Fehler:
    InternSendData = False
End Function
 
....
 
Private Sub SubClass()
    '-------------------------------------------------------------
    'Initiates the subclassing of this UserControl's window (hwnd).
    'Records the original WinProc of the window in mWndProcOrg.
    'Places a pointer to the object in the window's UserData area.
    '-------------------------------------------------------------
 
    'Exit if the window is already subclassed.
    If mWndProcOrg Then Exit Sub
 
    'Redirect the window's messages from this control's default
    'Window Procedure to the SubWndProc function in your .BAS
    'module and record the address of the previous Window
    'Procedure for this window in mWndProcOrg.
    mWndProcOrg = SetWindowLong(hWnd, GWL_WNDPROC, AddressOf SubWndProc)
 
    'Record your window handle in case SetWindowLong gave you a
    'new one. You will need this handle so that you can unsubclass.
    mHWndSubClassed = hWnd
 
    'Store a pointer to this object in the UserData section of
    'this window that will be used later to get the pointer to
    'the control based on the handle (hwnd) of the window getting
    'the message.
     Call SetWindowLong(hWnd, GWL_USERDATA, ObjPtr(Me))
End Sub
 
'The address of this function is used for subclassing.
'Messages will be sent here and then forwarded to the
'UserControl's WindowProc function. The HWND determines
'to which control the message is sent.
Public Function SubWndProc(ByVal hWnd As Long, ByVal Msg As Long, ByVal wParam _
  As Long, ByVal lParam As Long) As Long
 On Error Resume Next
 
    'Get pointer to the control's VTable from the
    'window's UserData section. The VTable is an internal
    'structure that contains pointers to the methods and
    'properties of the control.
    ptrObject = GetWindowLong(hWnd, GWL_USERDATA)
 
    'Copy the memory that points to the VTable of our original
    'control to the shadow copy of the control you use to
    'call the original control's WindowProc Function.
    'This way, when you call the method of the shadow control,
    'you are actually calling the original controls' method.
    CopyMemory ctlShadowControl, ptrObject, 4
 
    SubWndProc = ctlShadowControl.WindowProc(hWnd, Msg, wParam, lParam)
 
    CopyMemory ctlShadowControl, 0&, 4
    Set ctlShadowControl = Nothing
End Function