c++ - Win32 SetForegroundWindow unreliable

Question

I have a rather complex series of applications which depend on the ability to switch applications in the foreground.

My problem is, every 5 or 6 times of switching the applications in the foreground, it simply fails to bring the application forward. GetLastError does not report any issues. Often times I see the correct application flash in the foreground for a moment then the previous application is visible.

I have a Manager application which I have source for, it spawns and controls about 4 applications which I do not have source for. one of the applications it spawns/controls is also a manager which spawns/controls about 5 applications.

This is a sort of kiosk design so the user wont even have a keyboard or mouse, just a touch screen.

I have tried every combination of the Win32 calls to control them I am just out of ideas.

My first attempt was:

SetWindowPos(hApp, HWND_TOPMOST, NULL, NULL, NULL, NULL, SWP_NOMOVE | SWP_NOSIZE);
SetWindowPos(hApp, HWND_NOTOPMOST, NULL, NULL, NULL, NULL, SWP_NOMOVE | SWP_NOSIZE);

My second attempt was:

SetForegroundWindow(hApp);
SetActiveWindow(hApp);
SetFocus(hApp);

my third attempt: DWORD dwThreadID = GetWindowThreadProcessId(hApp, NULL); AttachThreadInput( dwThreadID, GetCurrentThreadId(), true);

SetForegroundWindow(hApp);
SetActiveWindow(hApp);
SetFocus(hApp);

AttachThreadInput( dwThreadID, GetCurrentThreadId(), false);

my forth attempt:

DWORD dwThreadID = GetWindowThreadProcessId(hApp, NULL);
AttachThreadInput( dwThreadID, GetCurrentThreadId(), true);

SetWindowPos(hApp, HWND_TOPMOST, NULL, NULL, NULL, NULL, SWP_NOMOVE | SWP_NOSIZE);
SetWindowPos(hApp, HWND_NOTOPMOST, NULL, NULL, NULL, NULL, SWP_NOMOVE | SWP_NOSIZE);

SetForegroundWindow(hApp);
SetActiveWindow(hApp);
SetFocus(hApp);

AttachThreadInput( dwThreadID, GetCurrentThreadId(), false);

I feel like I am missing an important gotcha when it comes to window switching. I know that only the foreground process can switch windows around but as my main Manager program is spawning and starting all the other processes which I need to control, I feel like it should be capable of moving these windows around. Any suggestions or advice is appreciated.

Answer 1

I was having the same issue and I didn't want to mess up with threads. On experimenting I observed a simple hack to make SetForegroundWindow() work in the expected manner. Here is what I did:

1. Minimize the window if its not already minimized
2. Restore the minimized window
3. Call SetForegroundWindow(), and your window will be on top