Question

I’m trying to track focus changes between several TrackBars (aka sliders, all within the same window) using WTL.

So far I’ve tried a
MESSAGE_HANDLER(WM_SETFOCUS, func)
as well as one
COMMAND_HANDLER(IDC_SLIDERn, WM_SETFOCUS, func)
for each slider without success.

The about trackbar controls page on msdn says: “WM_SETFOCUS Repaints the trackbar window.” ..

edit:
I now have derived the sliders from my own class where I handle WM_SETFOCUS with MESSAGE_HANDLER and notify the parent window by posting the message to it with m_hWnd as lParam so I can check in the parent which slider gained focus.

This works, but is there a more elegant way to do this?

Answer 1

WM_SETFOCUS is sent to the specific window that gets focus, not to the parent, as you’ve discovered.

However, there’s an alternate tecnique that you can use to avoid subclassing; most controls (specifically the ‘common controls’, which includes sliders) will send a WM_NOTIFY to their parent when certain events happen, allowing the parent to handle these events for a collection of children.

In your case, try listening for WM_NOTIFY message at the parent window, specifically checking for the case where the notification ID is NM_SETFOCUS – from MSDN:

Notifies a control’s parent window that the control has received the input focus. This notification code is sent in the form of a WM_NOTIFY message.

…which sounds like what you are looking for. Apparently ATL supports these in the message map using NOTIFY_HANDLER, something like:

NOTIFY_HANDLER(IDC_SLIDERn, NM_SETFOCUS, func)

Note that this works because the Win32 Common Controls support this sort of notification forwarding; if you were to use some other custom control instead, you may not get these notifications and would have to resort to subclassing. But for the common controls, this is the simplest way of doing it.