The dialog manager, part 4: The dialog loop
The dialog loop is actually quite simple. At its core,
it's just
while (<dialog still active> &&
GetMessage(&msg, NULL, 0, 0, 0)) {
if (!IsDialogMessage(hdlg, &msg)) {
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
If you want something fancier in your dialog loop,
you can take the loop above and tinker with it.
But let's start from the beginning.
The work happens in DialogBoxIndirectParam.
(You should already know by now how to convert all
the other DialogBoxXxx functions into DialogBoxIndirectParam.)
INT_PTR WINAPI DialogBoxIndirectParam(
HINSTANCE hinst,
LPCDLGTEMPLATE lpTemplate, HWND hwndParent,
DLGPROC lpDlgProc, LPARAM lParam)
{
/*
* App hack! Some people pass GetDesktopWindow()
* as the owner instead of NULL. Fix them so the
* desktop doesn't get disabled!
*/
if (hwndParent == GetDesktopWindow())
hwndParent = NULL;
That's right, we start with an app hack.
The problem of passing GetDesktopWindow() instead of NULL
was discussed
in an earlier entry.
So many people make this mistake that we had to put this app hack
into the core OS. It would be pointless to make a shim for it
since that would mean that thousands of apps would need to be shimmed.
Since only top-level windows can be owners, we have to
take the putative hwndParent
(which might be a child window) and walk up the window hierarchy
until we find a top-level window.
if (hwndParent)
hwndParent = GetAncestor(hwndParent, GA_ROOT);
With that second app hack out of the way, we create the dialog.
HWND hdlg = CreateDialogIndirectParam(hinst,
lpTemplate, hwndParent, lpDlgProc,
lParam);
Note: As before, I am going to ignore error checking and
various dialog box esoterica because it would just be
distracting from the main point of this entry.
Modal windows disable their parent, so do it here.
BOOL fWasEnabled = EnableWindow(hwndParent, FALSE);
We then fall into the dialog modal loop:
MSG msg;
while (<dialog still active> &&
GetMessage(&msg, NULL, 0, 0)) {
if (!IsDialogMessage(hdlg, &msg)) {
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
Per the convention on quit messages, we re-post any
quit message we may have received so the next outer
modal loop can see it.
if (msg.message == WM_QUIT) {
PostQuitMessage((int)msg.wParam);
}
(Astute readers may have noticed an uninitialized
variable bug: If EndDialog was called during
WM_INITDIALOG handling, then msg.message is never set.
I decided to ignore this fringe case for expository purposes.)
Now that the dialog is complete, we clean up.
Remember to enable the owner before destroying the
owned dialog.
if (fWasEnabled)
EnableWindow(hwndParent, TRUE);
DestroyWindow(hdlg);
And that's all. Return the result.
return <value passed to EndDialog>;
}
Congratulations, you are now an expert on dialog boxes.
Tomorrow we'll look at how you can put this new expertise
to good use.
Exercise: Find a way to sneak through the two layers of
hwndParent parameter "repair" and end up with
a dialog box whose owner is the desktop window.
Explain the dire consequences of this scenario.
