Question

I originally had an ActiveX control that registered a Windows timer (with SetTimer()) that fires every few seconds. That worked fine so far. Now in order to implement a full screen mode, I added a child window to my control that is supposed to show the content while the control itself manages all the ActiveX stuff.

The problem that I have with this approach is that my WM_TIMER suddenly stops firing at some time. I have traced it back to UIDeactivate() being called on my control but I don’t know why this method is called (I believe it has something to do with losing focus) when it wasn’t called before.

I would also like to know why my WM_TIMER events suddenly stop while everything else still seems to work fine. And what could it have to do with showing the content in a child window instead of on the ActiveX control itself?

Answer 1

Timers stops for a reason. Which might be:

1. You do stop timer by KillTimer call
2. Your window is re-created and timer is not re-enabled
3. Your control is windowless and you actually don’t have a HWND handle
4. There is a collision in timer identifiers, there is something else (e.g. internal subclassed window) out there to use the same identifier, it sets, kill the timer and you no longer see WM_TIMER messages you enabled earlier
5. The window thread is busy (frozen) with some activity which does not include message dispatching, so timer itself exists, is healthy and alive, just no messages sent

The things to do – without yet additional information on the issue on hands:

1. Check threads of your window, and your Set/KillTimer calls to make sure they all make sense together
2. Use Spy++ tool to check messages posted for your window and/or in the thread of the interest, to find out if you really have WM_TIMERs missing, or they just don’t reach your code; also you might see other interesting messages around