MFC CDialog/CDialogEx DoModal ALT

Questions:

I'm using MFC CDialog/CDialogEx to show a modal dialog with DoModal.
usually it works without problems, but sometimes, the dialog wont show up until I press ALT key.

the scenarios is, I have a timer in the parent window, and doing some work in the OnTimer function, if the work takes too much time, say, longer than the timer interval, then DoModal wont show the dialog window, until ALT key pressed.

I've traced the problem into CWnd::RunModalLoop() function in wincore.cpp
apparently it can only call ShowWindow() when the message loop is empty,
or, a message 0x118 (WM_SYSTIMER) or WM_SYSKEYDOWN (ALT key) is received.
since my parent window is always busy processing WM_TIMER message, the message queue will never be empty, it will never call ShowWindow() to display the dialog window, until I press ALT key.

I think is behaviour is unexpected.

Answers:

Hello,

Thanks again for the report. We have investigated this issue and we feel that it is by design. All time-consuming operations should be placed in separate (working) threads and then pass progress info to the main GUI thread. This MSDN topic has more information: 
http://msdn.microsoft.com/en-us/library/windows/desktop/dd744765(v=vs.85).aspx

I hope this helps.

Pat Brenner
Visual C++ Libraries Development

Solutions：

call CWnd::PostMessage(0x118) before DoModal();