Re: Message Reflection


"John Carson" <jcarson_n_o_sp_am_@xxxxxxxxxxxxxxx> wrote in message
news:%23S8AgPIcFHA.132@xxxxxxxxxxxxxxxxxxxxxxx
> "Steve Thresher" <steve.thresher@xxxxxxxxxxxxxx> wrote in message
> news:ePXSC5EcFHA.3464@xxxxxxxxxxxxxxxxxxxx
>> "John Carson" <jcarson_n_o_sp_am_@xxxxxxxxxxxxxxx> wrote in message
>> news:u0OBGHDcFHA.580@xxxxxxxxxxxxxxxxxxxxxxx
>>> "Steve Thresher" <steve.thresher@xxxxxxxxxxxxxx> wrote in message
>>> news:eLuyi5CcFHA.3808@xxxxxxxxxxxxxxxxxxxx
>>>> 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
>

I've been giving the problem a bit more thought and have decided to try and
use a message hook instead. When I receive a WM_NOTIFY message I will pass
it to the child control and if it's not handled I will allow it to go
through to the parent control.

Thanks for trying to help.

Steve.


.

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