[Interest] Handling WM_QUIT messages when no window is shown
Julius Bullinger
julius.bullinger at gmail.com
Thu May 7 11:38:24 CEST 2020
On 06.05.2020 14:57, Henry Skoglund wrote:
> Hi, when running apps on Windows without a window, you'll be missing out
> on a lot of inter-process stuff like WM_QUIT (that's why it's common for
> windowless apps to create a hidden, non-interactive window just to be
> able to receive all those WM_XXX). So no aboutToQuit() will be emitted
> for you when you skip creating that widget window.
How would one create a hidden, non-interactive window with Qt?
> But there's an API for windowless apps where you can receive a control
> signal, e.g. Ctrl-C was pressed or someone (like the Task Manager) is
> shutting down the app, more here:
> https://docs.microsoft.com/en-us/windows/console/setconsolectrlhandler
> and the callback:
> https://docs.microsoft.com/en-us/windows/console/handlerroutine
>
> There's no support for that API in Qt but it's pretty easy to use.
> Here's an example, I created a vanilla Qt console app, and changed
> main.cpp to this:
> -----------------------------------------
> #include <QCoreApplication>
> #include <windows.h>
>
> BOOL WINAPI CtrlHandler(DWORD fdwCtrlType)
> {
> switch (fdwCtrlType)
> {
> case CTRL_CLOSE_EVENT:
> ::OutputDebugStringA("Ctrl-Close event"); // catch taskkill or
> Task Manager End task
> return TRUE;
>
> default:
> return FALSE;
> }
> }
>
> int main(int argc, char *argv[])
> {
> QCoreApplication app(argc, argv);
>
> SetConsoleCtrlHandler(CtrlHandler, TRUE);
>
> return app.exec();
> }
> -----------------------------------------
> Note: I'm using OutputDebugString and DbgView.exe to view the output,
> qDebug() output has a tendency to disappear when you test with "End
> task" from TaskManager.
>
> Note 2: this API is very flakey if you try it from a GUI-built .exe, for
> Qt apps I mean built with "QT += core gui etc" in the .pro file, and use
> of QApplication in main.cpp. Instead you need to build your app like a
> Qt console app, "QT -= gui" and CONFIG += console, and use
> QCoreApplication in main.cpp, like in my example above.
That's the solution we're using in plain console QCoreApplications.
However, in this case, we have a QApplication which is showing or not
showing a GUI depending on some commandline args. So that will probably
not work robustly in this situation.
Thanks!
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