Re: Message Reflection

"Steve Thresher" <steve.thresher@xxxxxxxxxxxxxx> wrote in message
news:ePXSC5EcFHA.3464@xxxxxxxxxxxxxxxxxxxx

"John Carson" <jcarson_n_o_sp_am_@xxxxxxxxxxxxxxx> wrote in message
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"Steve Thresher" <steve.thresher@xxxxxxxxxxxxxx> wrote in message
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Can anyone tell me how message reflection should be implemented or
point me at a reference on the topic. I am NOT using MFC. I am
attempting to custom draw a header control and need to know how to
get the WM_NOTIFY message from the parent control to my window
procedure for the header control. I can subclass the parent of the
header control when it is created but what happens when you destroy
the header control? The parent window is still sub-classed with no
way to work out the address for the parents original window
procedure. Any help would be greatly appreciated.

Steve. 

I am puzzled by your question. When you subclass a window procedure,
the address of the original window procedure is received as the
return value of SetWindowLong. You need this address so you can call
the original window procedure for those messages you don't choose to
process. You can choose to remove the subclass when you destroy the
header
control for the sake of a slight efficiency gain, but it should
continue to work if you just leave it there unless you have written
it in some strange way. --
John Carson


You MUST NOT unsubclass a window on operating systems prior to XP /
2003 as you cannot guarantee that no-one else has subclassed the
window; XP / 2003 provide functions to subclass / unsubclass a
window.

You could presumably check (using GetWindowLong) if the current window
procedure is the one you set. If it is, then no-one else has subclassed it after you. If it isn't, you leave the subclass in place. Easier still, just leave it in place.

Also once the header control has been destroyed, so has the
data attached to the window which includes the original window
procedure address.


I am still puzzled.

MFC includes some kind of message relection
technique which I was hoping to implement in pure Win32 code. I was
just hoping someone would have some idea how to do it.


When it receives the WM_NOTIFY method, the parent checks the ID of the
sender to see if it comes from the header control. If so, it calls

return SendMessage(((NMHDR)lParam).hwndFrom, message, wParam, lParam);

If you want reflection to every child control, you can skip the check.

--
John Carson

.

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