Why does the task bar appear when I display a self-drawn modeless dialog? .. sometimes?

Question

I have an interesting (but frustraring) problem. I have an application which uses the full screen (this is meant to simulate a third-party fullscreen POS application).

My application displays a sequence of modeless dialog boxes on top of the full screen application. It shows one, hides it, then shows the next, hides it etc. After the 3rd show, the Windows taskbar appears about 1 second later. I can't figure out why.

I've stripped my code right back to see if its something I'm doing in my OnNcActivate handler (which I use to draw my skinned window) but I don't think it is as the problem appears to be timing related. I've tried running Spy++ as well as dumping messages in m WindowProc myself and I still can't see anything odd that would give me any clues.

There are some messages with ID 0x36e in my logs but I can't find out what they are supposed to be. I've checked various message ID lists and can't find them. They shouldn't be any message IDs of my own since WM_USER doesn't start until 0x400.

I know I could get around this problem by auto-hiding the taskbar but I can't ask our customers to configure their taskbars to auto-hide to get round my problem.

Any ideas why the taskbar would appear in relation to my modeless dialog boxes?

EDIT: I completely stripped out my self-drawn GUI code and I still have the same problem. I could be wrong but it would seem that when I call ShowWindow( SW_HIDE) first, Windows tries to activate "another Window" (as it says in MSDN). I think in this case its activating the taskbar rather than the POS application. If on the other hand I open my second window before calling ShowWindow( SW_HIDE ) on the second, then it seems to behave itself.

Cheers Sparky

Answer 1

Following a long discussion I come to the conclusion that DestroyWindow was not the problem. I found in the end that displaying a dialog.. clicking on the POS, then clicking back on the dialog that sometimes the taskbar would appear. I have spent an entire week trying to find reasons for all of this but to no avail. I thought that assigning the POS window as the owner would solve the problem - it didn't. In the end the solution for my problem was to determine if the taskbar is obscured completely before showing my dialog. If it is, I hide the taskbar for the duration which my dialog is displayed (set its placement to SW_HIDE) and then set it to SW_SHOW when I close my dialog. The task bar doesn't pop up and annoy people anymore. Not a fantastic solution for other peoples' applications perhaps, but perfect for our customers.