How to check if the application has been minimized - qt

Question

Whenever the application window is minimized or maximized i want to link that signal with a function.
This is the code.
int main(int argc, char *argv[])
{
QApplication application(argc, argv);
Renderer w(model ); // This is QWidget
w.show();
QObject::connect(&w, &QWindow::windowStateChanged, [&](Qt::WindowState state) {
});
// how will i define the QObject::connect
return application.exec();
}
What would be the parameters for the QObject::connect function ?

Answer 1

You cannot use the connect function to connect to different slots based on the given value. You can however simply call the functions based on the value by checking the value in your lambda.
At least, you could if you had the signal. However, your connect suggests that w is - or inherits - a QWindow. You can obviously only connect to signals your class provides. As your Renderer is a QWidget, you have to check that class.
The documentation of QWidget tells us, that there is no windowStateChanged signal, but it states:
When the window state changes, the widget receives a changeEvent() of type QEvent::WindowStateChange.
So therefor we can create our own signal and connect to that. This can look similar to the following working example:
#ifndef RENDERER_H
#define RENDERER_H
#include <QWidget>
#include <QEvent>
class Renderer : public QWidget {
Q_OBJECT
signals:
void stateChanged(bool isMaximized);
protected:
void changeEvent(QEvent *e)
{
if(e->type() == QEvent::WindowStateChange) {
emit stateChanged(windowState() & ~Qt::WindowMaximized);
}
QWidget::changeEvent(e);
}
};
#endif // RENDERER_H
int main(int argc, char *argv[])
{
QApplication application(argc, argv);
Renderer w; // This is QWidget
w.show();
QObject::connect(&w, &Renderer::stateChanged, [&](bool maximized) {
qDebug() << "Maximized?" << maximized;
});
return application.exec();
}

Answer 2

I was able to solve by using QApplication::focusWindow()
int main(int argc, char *argv[])
{
QApplication application(argc, argv);
Renderer w; // This is QWidget
w.show();
QObject::connect(QApplication::focusWindow(), &Renderer::stateChanged, [&](bool maximized) {
qDebug() << "Maximized?" << maximized;
});
return application.exec();
}