Proper way to handle the close button in a main window PyQt, (Red "X")

Question

First off, I am a complete newbie to PyQt.

I have been trying to link a function to the Main Window's close button (the red x in the corner of the window) but I haven't been having any success. Right now, my code looks something like this:

class Ui_MainWindow(QtGui.QMainWindow):
    def __init__(self):
        QtGui.QMainWindow.__init__(self)
        self.setupUi(self)
    def setupUi(self, MainWindow):
        #setup code goes here
    def retranslateUi(self, MainWindow):
        #re translation of the GUI code 
    def closeEvent(self, event):
        print "User has clicked the red x on the main window"

In a seperate "main" file I have the folowing:

class GUIForm(QtGui.QMainWindow):
    def __init__(self, parent=None):
        QtGui.QMainWindow.__init__(self,parent)
        self.ui = Ui_MainWindow()
        self.ui.setupUi(self)
        #self.ui.ECUStatus_txt = MyWidget.__init__.text_list
        self.threadData()


    if __name__ == "__main__":

        app = QtGui.QApplication(sys.argv)
        myapp = GUIForm()
        myapp.show()
        ret = app.exec_()
        sys.exit(ret)

However, when I run via command prompt, I am not able to see the print statement when I hit the red x. I know I am new to Qt, but I have seen quite a few people ask this question, and none of the answers seemed to get beyond what is already written above.

One of these answers: Answer #1 Answer #2

Both of these solutions are similar to mine, but it still doesn't work

Despite the answer, which may have worked for that user's specific code, my fellow PyQt colleagues and I are still quite foggy on the reasoning ours is not working. Is there a defined button name for the "Red X box" built into PyQt? Can I connect it to another function the someway I would for other buttons?

Answer 1

You shouldn't ever modify the class that was generated from your ui file. Instead you should subclass and modify the subclass.

From the looks of your code, you are actually creating two QMainWindows and the closeEvent is being caught for the wrong one (presumably that one is hidden?). That is self.ui is a QMainWindow that is not being shown, and is not added to the UI of GUIForm. Instead you are using the Ui_MainWindow.setupUi() method explicitly yourself, to add the widgets to your own QMainWindow, 'GUIForm`.

Instead, what you should to do is leave your Ui_MainWindow class as it was when it was generated from the ui file, and then modify your main python file to be:

class GUIForm(Ui_MainWindow):
    def __init__(self, parent=None):
        Ui_MainWindow.__init__(self, parent)
        self.threadData()

    def closeEvent(self, event):
        print "User has clicked the red x on the main window"
        event.accept()


if __name__ == "__main__":

    app = QtGui.QApplication(sys.argv)
    myapp = GUIForm()
    myapp.show()
    ret = app.exec_()
    sys.exit(ret)

This way you are extending the behaviour of the auto-generated UI file. This makes it easy to regenerate the python file from the .ui file without having to re-add code (this is precisely why you should never modify the auto-generated Python file)

Answer 2

Sometimes, issues occur when handling event signals from the main window.

You can use the code :

app.aboutToQuit.connect(self.closeEvent)

and you can write your own code in the closeEvent function.

Note :

app is the name of the QtGui.QApplication instance

Here's a demo of the full code :

from PyQt4 import QtCore, QtGui

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(800, 600)
        self.centralwidget = QtGui.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        MainWindow.setCentralWidget(self.centralwidget)
        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

        #{================================

        app.aboutToQuit.connect(self.closeEvent)

        #}================================

    def retranslateUi(self, MainWindow):
        MainWindow.setWindowTitle('Demo')

    #{================================

    def closeEvent(self):
        #Your desired functionality here
        print('Close button pressed')
        import sys
        sys.exit(0)

    #}================================


if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)
    MainWindow = QtGui.QMainWindow()
    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)
    MainWindow.show()
    sys.exit(app.exec_())

Hope it helps.