how to ignore the event when I click on the button to maximize the window (windowMaximizeButtonHint())

Domenico

I tried with:

MainWindow.h

virtual void changeEvent(QEvent* event);

MainWindow.cpp

void MainWindow::changeEvent(QEvent *event)
{
if(event->type() == QEvent::WindowStateChange)
{
hide();
event->ignore();
}
return QMainWindow::changeEvent(event);
}

I know that the button event is not square Qt::WindowMaximizeButtonHint (). but with codes as indicated above if I click on that button the window disappears or rather the application disappears. why? what's wrong?

JonB

@Domenico
First: I think when you hide() the main window, and it's the only window, that causes application exit. Why did you put that in anway, you just want to try to ignore() the event?

Second: I happened to be looking at something similar last week. See https://forum.qt.io/topic/104184/is-it-possible-to-intercept-maximizing-the-main-window. In my case I wanted to intercept the maximize window button to not do maximization and instead something of my own. The conclusion I came to was: this event only seems to be signalled after the native windowing system has done what is supposed to be done when the maximize button is clicked. You can react to it yourself in the slot, but you cannot stop the window maximizing. That was my conclusion. I left it open because I still didn't hear some definitive statement as to whether this is correct by one of the experts here.

Cobra91151

@Domenico @JonB

Hello! First of all, you can set for example: setWindowFlags(Qt::Dialog | Qt::WindowCloseButtonHint);, so your dialog no longer have maximize button. But If you really want to intercept the maximize event here is my code:

bool Test::event(QEvent *event)
{
    if (event->type() == QEvent::WindowStateChange) {
        if (this->isMaximized()) {
            this->showNormal();
        }
    }

    return QWidget::event(event);
}

It's a bit tricky, but it handles such task. Also, there is option using Win API intercepting SW_SIZE, SW_SIZING messages using Qt bool QWidget::winEvent(MSG * message, long * result): https://doc.qt.io/archives/qt-4.8/qwidget.html#winEvent

Happy coding!

JonB

@Cobra91151
In my case (as per https://forum.qt.io/topic/104184/is-it-possible-to-intercept-maximizing-the-main-window), as I said there the code you show results in the window first being maximized by the OS window system, which the user sees, followed by it being restored to normal size. That is actually the kind of thing I ended up having to use, but it is not what I would call "intercepting" or "ignoring" the maximize button.

Cobra91151

@JonB

Try to use winEvent it will help to actually intercept any OS message including maximize. Win API docs: https://docs.microsoft.com/en-us/windows/desktop/winmsg/wm-size
https://docs.microsoft.com/en-us/windows/desktop/winmsg/wm-sizing

JonB

@Cobra91151
How will that help me given that I use Qt for platform independence? I support Windows & Linux, like many people.... The OP has never mentioned Windows-only.

Cobra91151

@JonB

It is not possible to make it working using Qt for platform independence. Because it doesn't have such feature built in. The only easy way is to use platform specific code and add checks for different OS, such as Windows and Linux. You can also try to write portable lib/code by yourself omitting Qt.

By the way, Qt framework works the same, it has platform specific code and checks which one to use behind the scene :)

Also, I would like to mention new Qt method:

bool QWidget::nativeEvent(const QByteArray &eventType, void *message, long *result)

Docs: https://doc.qt.io/qt-5/qwidget.html#nativeEvent

Cobra91151

@JonB @Domenico

So here is with nativeEvent and platform checks for Windows and Linux.

bool Test::nativeEvent(const QByteArray &eventType, void *message, long *) {
    qDebug() << eventType;
    MSG *msg = static_cast<MSG *>(message);

#ifdef __linux__
    //Linux code here
#elif _WIN32
    if (msg->message == WM_SYSCOMMAND) {
        if (msg->wParam == SC_MAXIMIZE) {
            QMessageBox::information(this, "Test", "Maximizing...", QMessageBox::Ok);
            //Add your code here
            return true;
        }
    }
#endif

    return false;
}

Screenshot:

Domenico

@JonB @Cobra91151
thanks a lot to everyone!! worked with the method:

bool QWidget::nativeEvent(const QByteArray &eventType, void *message, long *result)

With this method it does not allow to enlarge the window when I click on maximizes! is the code I meant. also the code:

bool Test::event(QEvent *event)
{
if (event->type() == QEvent::WindowStateChange) {
if (this->isMaximized()) {
this->showNormal();
}
}

return QWidget::event(event);

}

They are fine but it is not ignored if you click the button before it enlarges and immediately afterwards it returns to normal, it is not what I meant. Thanks again!

Pl45m4

@Domenico said in how to ignore the event when I click on the button to maximize the window (windowMaximizeButtonHint()):

bool Test::event(QEvent *event)
{
if (event->type() == QEvent::WindowStateChange) {
if (this->isMaximized()) {
this->showNormal();
}
}
return QWidget::event(event);

}
They are fine but it is not ignored if you click the button before it enlarges and immediately afterwards it returns to normal, it is not what I meant.

This is the normal behavior for this code. The QEvent can not prevent the OS from maximizing the window. So your window will maximize first, before the event sets it back to normal size.