Re: Custom Control - Notifcation Messages

From:

"Scott McPhillips [MVP]" <org-dot-mvps-at-scottmcp>

Newsgroups:

microsoft.public.vc.mfc

Date:

Sat, 04 Aug 2007 22:23:23 -0400

Message-ID:

<ctSdnXtPWvICqSjbnZ2dnUVZ_vumnZ2d@comcast.com>

Nobody wrote:

Hi,

I just started messing around with creating my own custom control notification messages,
so I am just curious about the inner workings of notifcation messages.
This is more or less just the philosphy behind notification messages and how they work.

Here, I have created my own notification message.
struct MOUSE
{
HWND hwndFrom;
UINT idFrom;
UINT code;
UINT nFlags;
CPoint point;
};

In the class, I extantiate the object
class CSomeControl
{
private:
    MOUSE Mouse;
}

Then, in OnLButtonDown, OnLButtonUp, OnMouseMove, I send a Notifcation message.
if(GetMouseEvents()) //If MouseEvents Notifcation Messages Enabled
{
  Mouse.hwndFrom = GetSafeHwnd();
  Mouse.idFrom = ID_MYCONTROL;
  Mouse.code = UWM_MYCONTROL_LBUTTONDOWN;
  Mouse.nFlags = nFlags;
  Mouse.point = point;
  GetParent()->PostMessage(WM_NOTIFY, UWM_MYCONTROL_LBUTTONDOWN, (LPARAM)&Mouse);
}

Is that basically how it is done?

No, this has a bad bug. PostMessage returns to you before the message
is processed. Then OnMouseMove might occur before the message is
processed, so you PostMessage again but you have now wiped out the
previous data in the Mouse struct, even though the handler of the first
message has not seen it yet. Solution: You must use SendMessage instead
of PostMessage. SendMessage does not return until the message has been
processed.

--
Scott McPhillips [MVP VC++]