Get application quit signal before windows are closed in QT - qt

Question

I have a Qt Application with multiple main windows and want to get a signal when the App is about to quit while all windows are still up.
The QApplication.aboutToQuit signal doesn't work for me because it only fires after all windows have been closed.
All other answers I've seen suggest implementing the main window's closeEvent() function, but I have multiple main windows and I couldn't find any way to differentiate CloseEvents between a normal closeEvent of just a single window being closed and a close event from when the whole application is closing after QMD+Q or the using clicking quit in the task bar or for whatever reason it quits.
How do I get a signal for that only when the whole application is about to quit but before any windows are closed?
What happens when I press Cmd+Q or right click quit the task bar icon:
(I want a signal at this point) <-
all windows get a closeEvent()
aboutToQuit() fires
app quits
What I want is to get a signal before any of that happens and all the windows are still open.
Edit: minimal example
from PyQt5.QtGui import QCloseEvent
from PyQt5.QtWidgets import QApplication, QWidget
class Win(QWidget):
def closeEvent(self, event: QCloseEvent):
# implementing a custom closeEvent doesn't help me
# this is called for every normal manual window close and when the application quits
# I only want to run something when the full application gets shut down, not just this window
# can't see any way to differentiate between the two
print("closeEvent", event.type(), event)
return super().closeEvent(event)
if __name__ == '__main__':
app = QApplication([])
app.aboutToQuit.connect(lambda :print("about to quit, this is too late, by now all windows are closed"))
#What I need
# app.beforeQuitSignal.connect(lambda :print("signal that it's gonna quit, before any of the windows are closed"))
#stuff I've tried that didn't work either
app.quit = lambda *args:print("quit, doesnt get called")
app.exit = lambda *args:print("exit, doesnt get called")
app.closeAllWindows = lambda *args:print("closeAllWindows, doesnt get called")
mainwins = []
for i in range(5):
win = Win()
win.setGeometry(100*i,100*i, 400,400), win.show(), win.raise_()
mainwins.append(win)
app.exec_()

Answer 1

If you want to fire a signal when the user close a window but do not exit the QApplication immediately after the last window is closed, you can use QApplication.setQuitOnLastWindowClosed()
from PyQt5.QtCore import pyqtSignal
from PyQt5.QtGui import QCloseEvent
from PyQt5.QtWidgets import QApplication, QWidget
class Win(QWidget):
closing = pyqtSignal()
def closeEvent(self, event: QCloseEvent):
print("Window {} closed".format(self))
self.closing.emit()
return super().closeEvent(event)
class MyApp(QApplication):
def __init__(self, *args):
super(MyApp, self).__init__(*args)
self.setQuitOnLastWindowClosed(False)
self.lastWindowClosed.connect(self.onLastClosed)
self.mainwins = []
for i in range(5):
win = Win()
win.setGeometry(100 * i, 100 * i, 400, 400), win.show(), win.raise_()
self.mainwins.append(win)
def onLastClosed(self):
print("Last windows closed, exiting ...")
self.exit()
if __name__ == '__main__':
app = MyApp([])
app.exec_()
With this, when a window is closed, a closing() signal is emited

Answer 2

You can filter on the CloseEvent if it is spontaneous :
from PyQt5.QtCore import pyqtSignal, QEvent
from PyQt5.QtGui import QCloseEvent
from PyQt5.QtWidgets import QApplication, QWidget
class Win(QWidget):
closing = pyqtSignal()
def closeEvent(self, event: QCloseEvent):
self.closing.emit()
if event.type() == QEvent.Close and event.spontaneous():
event.ignore()
else:
return super().closeEvent(event)
class MyApp(QApplication):
def __init__(self, *args):
super(MyApp, self).__init__(*args)
self.mainwins = []
for i in range(5):
win = Win()
win.closing.connect(self.beforeQuit)
win.setGeometry(100 * i, 100 * i, 400, 400), win.show(), win.raise_()
self.mainwins.append(win)
def beforeQuit(self):
print("Exiting")
# Do what you want here ...
self.exit() # Terminate the QApplication
if __name__ == '__main__':
app = MyApp([])
app.exec_()

Answer 3

Use installEventFilter to intercept the application's quit event before any windows are closed:
class AppManager(QObject):
def __init__(self):
super().__init__()
qApp.installEventFilter(self)
def eventFilter(self, obj, event):
if event.type() == QEvent.Quit:
self.saveWindowStates()
return False
def saveWindowStates(self):
# code to save the application's state