Hi,

Is there a reason why I can't send and receive a messages with a
negative number using SendMessage?

The Windows common controls use negative notification messages and
I've never had a problem receiving those, so the problem has to be
with the Sending side of things.

What am I missing?

Thanks


'**** FORM1 ****'
Option Explicit

Private Declare Function SendMessage Lib "USER32" Alias "SendMessageA"
( _
  ByVal hWnd As Long, ByVal Msg As Long, wParam As Any, lParam As Any
_
) As Long

Private Declare Function SetWindowSubclass Lib "comctl32" ( _
  ByVal hWnd As Long, ByVal pfnSubclass As Long, _
  ByVal uIdSubclass As Long, ByVal dwRefData As Long _
) As Long

Private Declare Function DefSubclassProc Lib "comctl32" ( _
  ByVal hWnd As Long, ByVal wMsg As Long, _
  ByVal wParam As Long, ByVal lParam As Long _
) As Long

Private Declare Function RemoveWindowSubclass Lib "comctl32" ( _
  ByVal hWnd As Long, ByVal pfnSubclass As Long, _
  ByVal uIdSubclass As Long _
) As Long

Friend Function WndProc(ByVal hWnd As Long, ByVal uMsg As Long, _
  ByVal wParam As Long, ByVal lParam As Long) As Long

  Select Case uMsg
    Case -2049
      Debug.Print "-2049"
    Case Else
      WndProc = DefSubclassProc(hWnd, uMsg, wParam, lParam)
  End Select
End Function

Private Sub Form_Load()
  Call SetWindowSubclass(Me.hWnd, AddressOf Module1.WndProc,
ObjPtr(Me), 0&)
  Call SendMessage(Me.hWnd, -2049, ByVal 0&, ByVal 0&)
End Sub

Private Sub Form_Unload(Cancel As Integer)
  Call RemoveWindowSubclass(Me.hWnd, AddressOf Module1.WndProc, _
ObjPtr(Me))
End Sub

'**** MODULE1 ****'
Option Explicit

Public Function WndProc(ByVal hWnd As Long, ByVal uMsg As Long, _
  ByVal wParam As Long, ByVal lParam As Long, _
  ByVal uIdSubclass As Form1, ByVal dwRefData As Long _
) As Long

  WndProc = uIdSubclass.WndProc(hWnd, uMsg, wParam, lParam)
End Function

What is the constant for -2049? I already looked at the common controls
constants, but couldn't find a corresponding constant. Here are the list of
notification constants:


//====== WM_NOTIFY codes (NMHDR.code values)
==================================

#define NM_FIRST                (0U-  0U)       // generic to all controls
#define NM_LAST                 (0U- 99U)

#define LVN_FIRST               (0U-100U)       // listview
#define LVN_LAST                (0U-199U)

// Property sheet reserved      (0U-200U) -  (0U-299U) - see prsht.h

#define HDN_FIRST               (0U-300U)       // header
#define HDN_LAST                (0U-399U)

#define TVN_FIRST               (0U-400U)       // treeview
#define TVN_LAST                (0U-499U)

#define TTN_FIRST               (0U-520U)       // tooltips
#define TTN_LAST                (0U-549U)

#define TCN_FIRST               (0U-550U)       // tab control
#define TCN_LAST                (0U-580U)

// Shell reserved               (0U-580U) -  (0U-589U)

#define CDN_FIRST               (0U-601U)       // common dialog (new)
#define CDN_LAST                (0U-699U)

#define TBN_FIRST               (0U-700U)       // toolbar
#define TBN_LAST                (0U-720U)

#define UDN_FIRST               (0U-721)        // updown
#define UDN_LAST                (0U-740)
#if (_WIN32_IE >= 0x0300)
#define MCN_FIRST               (0U-750U)       // monthcal
#define MCN_LAST                (0U-759U)

#define DTN_FIRST               (0U-760U)       // datetimepick
#define DTN_LAST                (0U-799U)

#define CBEN_FIRST              (0U-800U)       // combo box ex
#define CBEN_LAST               (0U-830U)

#define RBN_FIRST               (0U-831U)       // rebar
#define RBN_LAST                (0U-859U)
#endif

#if (_WIN32_IE >= 0x0400)
#define IPN_FIRST               (0U-860U)       // internet address
#define IPN_LAST                (0U-879U)       // internet address

#define SBN_FIRST               (0U-880U)       // status bar
#define SBN_LAST                (0U-899U)

#define PGN_FIRST               (0U-900U)       // Pager Control
#define PGN_LAST                (0U-950U)

#endif

#if (_WIN32_IE >= 0x0500)
#ifndef WMN_FIRST
#define WMN_FIRST               (0U-1000U)
#define WMN_LAST                (0U-1200U)
#endif
#endif

#if (_WIN32_WINNT >= 0x0501)
#define BCN_FIRST               (0U-1250U)
#define BCN_LAST                (0U-1350U)
#endif

on 8/29/2010, Robert supposed :
I think you may have a problem with sign.  Windows Messages are
unsigned values - some of them look negative to VB.CLASSIC, because it
does not support an unsigned type.  What windows is seeing is going to
be:

Dim b As Long
b = CLng("&H" & Hex$(-2049))

Which is the value: 63487

Which is &HF7FF  and in fact, when that hex value is assigned to a vb
long, you get 63487.

So, my guess is that the value you are receiving is 63487, since that
is under the value of 65536.

Show quote Hide quote Incorrect. The parameter is As Long, so -2049 gets sign extended to 32-Bit,
and would be &HFFFFF7FF.

Nobody was thinking very hard :
Show quoteHide quoteYes... I realized that as I was driving away from my home just a few
minutes after posing. For some reason, I was thinking in 16-bit 2's
complement rather then 32-bit.

Anyway, the number the op is looking for is really 4294965247

On Sun, 29 Aug 2010 14:44:51 -0600, Tom Shelton
<tom_shelton@comcast.invalid> wrote:

Show quoteHide quoteThat's the number I want any language that has unsigned 32 bit
integers, to think I am sending.

I actually want to send -2049

To put it in context:

For reasons* which become less compelling by the hour, I'm writing a
Win32 style control in VB6 (i.e. The window is created with
CreateWindowEx and the api is all windows messages).

-2049 is just the constant I'd picked to represent a left button click
following the common controls convention of using negative numbers to
define notifications.

If it was a C header the definition would be:

#define CVN_FIRST       (0U-2048U)
#define CVN_BUTTONCLICK (CVN_FIRST-1)

Which should translate to VB6 as:

Public Const CVN_FIRST = -2048&
Public Const CVN_BUTTONCLICK = CVN_FIRST - 1

Control Code:

If (SendMessage(m_hwndParent, CVN_BUTTONCLICK, ByVal 0&, nmhti) then
  ...
End if

The message isn't being received by the parent at all. Surely Windows
doesn't care (or know) that I'm sending a signed vb long rather than a
UINT.

Robert

*The main reason being that I wanted to see if I could.

Oh bugger, I've just realised that I'm getting this completely wrong.

I'm talking about notification messdages so CVN_BUTTONCLICK would be
contained in the code field of an NMHDR structure received in the
lParam of a WM_NOTIFY message.

Please pretend this thread never happened.

Robert

On Mon, 30 Aug 2010 05:34:56 +0100, Robert <non***@noserver.com>
wrote:

<snip>
Remarkable how many times I've typed up a question and realized I was
a moron at the bottom.   Thankfully before I posted.  <smile>

Tony

On Mon, 30 Aug 2010 05:34:56 +0100, Robert <non***@noserver.com>
wrote:

And here's what I should have been doing.

'Helper function

Private Function Notify(ByVal code as long, _
                        ByRef hdr as NMHDR) as long)
  hdr.hwndfrom = m_hwnd
  hdr.idFrom = GetDlgCtrlID(m_hwnd)
  hdr.code = code
  Notify = SendMessage(GetParent(m_hwnd), WM_NOTIFY, ByVal 0&, hdr)
End Function

'Calling code

  Dim itemclick as NMITEMCLICK
  itemclick.iItem = iItem
  '(fill in other fields)

  If (Notify(CVN_ITEMCLICK, itemclick.hdr)) Then
    ...
  End If

'Control parent code

    Case WM_NOTIFY
      Dim hdr As NMHDR
      CopyMemory hdr, ByVal lParam, LenB(hdr)
      If (hdr.hwndFrom = m_hwnd) Then
        Select Case hdr.code
          Case CVN_ITEMCLICK
            Dim itemclick As NMITEMCLICK
            CopyMemory itemclick, ByVal lParam, LenB(itemclick)
            Debug.Print "ITEMCLICK:", itemclick.iItem
        End Select
      End If

You shouldn't be doing hard sums whilst driving. It'll make your brain hurt
and you'll have an accident, which will make your brain hurt even more ;-)

Mike

Tom Shelton was thinking very hard :
                           ^^^^^^
Freudian slip, presumably? <eg>

Karl E. Peterson submitted this idea :
LOL... Darn typo!

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