SetFocus() fails with a valid window handle - c++

Question

I have a program with several custom controls. One of these custom controls is a text input control. Since a window does not automatically receive keyboard focus when you click on it, i've created a mouse hook in my program that calls SetFocus() on a window when the user clicks in that window. However, there is a problem.
If another program has focus when you click on my program's window (or any of the controls in that window) SetFocus() fails. I then have to click again for it to succeed. Here's the code:
LRESULT CALLBACK kbfProc(int nCode, WPARAM wParam, LPARAM lParam) // Keyboard focus switching procedure
{
switch(nCode)
{
case HC_ACTION:
{
if(wParam == WM_LBUTTONDOWN || wParam == WM_NCLBUTTONDOWN)
{
MOUSEHOOKSTRUCT * mhs = (MOUSEHOOKSTRUCT*) lParam;
if(SetFocus(mhs->hwnd) == NULL)
{
printf("SetFocus(Hwnd = %.8x) failed. Error code: %lu\n", mhs->hwnd, GetLastError());
} else {
printf("SetFocus(Hwnd = %.8x) returned success.\n", mhs->hwnd);
}
}
}
break;
}
return CallNextHookEx(0, nCode, wParam, lParam);
}
And the output of those printf calls is this:
SetFocus(Hwnd = 00410c06) failed. Error code: 87
SetFocus(Hwnd = 00410c06) returned success.
SetFocus(Hwnd = 01740fc8) failed. Error code: 87
SetFocus(Hwnd = 01740fc8) returned success.
Error code 87 is ERROR_INVALID_PARAMETER, but i'm obviously passing a valid window handle to the function, so why is it failing?

Answer 1

Whenever you're calling SetFocus, the window must be attached to the calling thread's message queue or SetFocus will return invalid if it's not. To workaround this, use SetForegroundWindow first when the mouse moves over your window before calling SetFocus.

Answer 2

I know I'm couple of days late, but since I just spent a whole day trying to fix this, I'll add my fix here as well, just in case it helps someone.
Basically it was the AttachThreadInput thing mentioned above in a comment. GetActiveWindow() was always returning NULL as well. Which window you need to attach to might vary case by case, but I needed the root window, so I used GetAncestor. If you know the window handle you want, then you can just use it instead. So this is the code that fixed it for me:
AttachThreadInput(GetCurrentThreadId(), GetWindowThreadProcessId(GetAncestor(hWnd, GA_ROOT), NULL), TRUE);

Answer 3

I've found a solution. After a lot of googling and trial & error I eventually came across this webpage (backup link). It goes over the behavior of window focus and activation in detail.
I ended up adding some code to the WM_ACTIVATE handler of my main window that searches for the child window that was clicked when the window is activated. Here's all the code:
Here's the hook procedure:
LRESULT CALLBACK kbfProc(int nCode, WPARAM wParam, LPARAM lParam)
{
switch(nCode)
{
case HC_ACTION:
{
if(wParam == WM_LBUTTONDOWN || wParam == WM_NCLBUTTONDOWN)
{
MOUSEHOOKSTRUCT * mhs = (MOUSEHOOKSTRUCT*) lParam;
BringWindowToTop(MainWindow->t_hwnd);
SetFocus(mhs->hwnd);
}
}
break;
}
return CallNextHookEx(0, nCode, wParam, lParam);
}
Here's the code i put in the WM_ACTIVATE handler:
case WM_ACTIVATE:
{
unsigned long state = (unsigned long) wParam & 0x0000FFFF;
unsigned long mState = (unsigned long) wParam & 0xFFFF0000;
if(state != 0)
{
...[some code here]...
FocusChildWindow(hwnd);
}
...[some code here]...
}
break;
And here's the FocusChildWindow() function:
void FocusChildWindow(HWND hwnd)
{
POINT mpos;
GetCursorPos(&mpos);
RECT wr;
GetWindowRect(hwnd, &wr);
mpos.x -= wr.left;
mpos.y -= wr.top;
HWND cw = ChildWindowFromPoint(hwnd, mpos);
if(cw == NULL || cw == hwnd)
{
SetFocus(hwnd);
} else {
GetCursorPos(&mpos);
HWND cw2;
while(1)
{
POINT sc = mpos;
MapWindowPoints(HWND_DESKTOP, cw, &sc, 1);
cw2 = ChildWindowFromPoint(cw, sc);
if(cw2 == NULL || cw2 == cw)
{
SetFocus(cw);
break;
} else {
cw = cw2;
}
}
}
}

Answer 4

The following worked for me when SetFocus() had no effect setting the keyboard focus to a child control window on a property sheet page window:
::SendMessage(m_hPropPageWnd, WM_UPDATEUISTATE, MAKEWPARAM(UIS_CLEAR, UISF_HIDEFOCUS), 0);