[PySide] QApplication::processEvents( ), re: Why doesn't this example work?

[Sean Fisk]

On Fri, Oct 24, 2014 at 2:48 PM, <peter_karasev at keysight.com> wrote:

>  Related question to this:
>
>  in C++ you can do this to make events start running before
> QApplication.exec() is called:
>
>
>
>
> *                QApplication::sendPostedEvents();
> QApplication::processEvents( );                 // if you do this in a
> while-loop, you can interact with widgets ... *
> Is it not possible to do this from PySide?
>
I’m not sure, but this:

QApplication::sendPostedEvents();
QApplication::processEvents();
 // if you do this in a while-loop, you can interact with widgets ...

…is pretty much what PySide.QtGui.QApplication.exec_() does (see here
<http://pages.citebite.com/n3n8v4q9r1dti>). So why not just use exec_(),
unless you have really specific requirements?
​

I tried to make a C++ wrapper object
> but it seemed like the PySide objects weren't getting updated, although
> C++ QT widgets would appear and allow you to interact before
> QApplication.exec() starts.
>
>         regards,
>      Peter Karasev
>
> ________________________________________
> От: pyside-bounces+peter_karasev=keysight.com at qt-project.org
> [pyside-bounces+peter_karasev=keysight.com at qt-project.org] от имени Jim
> Byrnes [jf_byrnes at comcast.net]
> Отправлено: 24 октября 2014 г. 11:29
> Кому: pyside at qt-project.org
> Тема: Re: [PySide] Why doesn't this example work?
>
> On 10/22/2014 11:26 PM, Sean Fisk wrote:
> > Hi Jim,
> >
> > With all due respect to the author of the book, I don’t think this is a
> > very good example. The most important thing to realize is that nothing
> > really happens before the event loop is started. The line:
> >
> > myApp.exec_()
> >
> > is what starts the event loop. Without the event loop running, windows
> > won’t appear, user input cannot be handled, and basically nothing
> > QtGui-related will work. *Even if* windows show up before the event loop
> is
> > started, they won’t be able to respond to user interaction (as far as I
> > understand).
> >
> > I would personally achieve the desired behavior like so:
> >
> > #!/usr/bin/env python
> > import sys
> > from PySide import QtCore, QtGui
> > class SampleWindow(QtGui.QWidget):
> > def __init__(self, parent=None):
> > super(SampleWindow, self).__init__(parent)
> > self.setWindowTitle('Sample Window')
> > self.setGeometry(300, 300, 200, 150)
> > self.setMinimumHeight(100)
> > self.setMinimumWidth(250)
> > self.setMaximumHeight(200)
> > self.setMaximumWidth(800)
> >
> > @QtCore.Slot()
> > def do_resize(self):
> > self.resize(300, 300)
> > self.setWindowTitle('Sample Window Resized')
> > def main(argv):
> > app = QtGui.QApplication(argv)
> >
> > # Create and show the window.
> > window = SampleWindow()
> > window.show()
> > # PySide windows don't auto-raise on Mac OS X.
> > window.raise_()
> >
> > # Set up a timer to fire 3 seconds *after the event loop starts*.
> > QtCore.QTimer.singleShot(3000, window.do_resize)
> >
> > # Start the event loop. Nothing Qt-related happens until this call.
> > return app.exec_()
> > if __name__ == '__main__':
> > raise SystemExit(main(sys.argv))
> >
> > The key take-away is that nothing QtGui-related *actually* happens before
> > the event loop is started, and everything is done by the time that it
> exits.
> >
> > Hope this helps. Feel free to let me know if anything doesn’t make sense.
> > ​
>
> Thanks for the code and the explanation. It works and I can follow it
> and understand what is happening.
>
> Thanks, Jim
>
> >
> > --
> > Sean Fisk
> >
> > On Wed, Oct 22, 2014 at 8:17 PM, Jim Byrnes <jf_byrnes at comcast.net>
> wrote:
> >
> >> In looking at the lists archives, I see that most of the participants
> >> seem to be experienced developers. As a novice programmer I hope I am
> >> not intruding by asking some basic questions.
> >>
> >> I am working my way through examples in a PySide book I bought.
> >> According to the author the example should display a 200 x 150 window,
> >> pause 3 seconds and then display a 300 x 300 window. On my system
> >> (Ubuntu 12.04) there is a approx 3 second delay after starting the
> >> program and then I see the 300 x 300 window. I never see the first
> window.
> >>
> >> Could someone explain to me why it does not act as described?
> >>
> >> # Import required modules
> >> import sys
> >> import time
> >> from PySide.QtGui import QApplication, QWidget
> >>
> >> class SampleWindow(QWidget):
> >> """ Our main window class
> >> """
> >>
> >> # Constructor function
> >> def __init__(self):
> >> QWidget.__init__(self)
> >> self.setWindowTitle("Sample Window")
> >> self.setGeometry(300, 300, 200, 150)
> >> self.setMinimumHeight(100)
> >> self.setMinimumWidth(250)
> >> self.setMaximumHeight(200)
> >> self.setMaximumWidth(800)
> >>
> >> if __name__ == '__main__':
> >> # Exception Handling
> >> try:
> >> myApp = QApplication(sys.argv)
> >> myWindow = SampleWindow()
> >> myWindow.show()
> >> time.sleep(3)
> >> myWindow.resize(300, 300)
> >> myWindow.setWindowTitle("Sample Window Resized")
> >> myWindow.repaint()
> >> myApp.exec_()
> >> sys.exit(0)
> >> except NameError:
> >> print("Name Error:", sys.exc_info()[1])
> >> except SystemExit:
> >> print("Closing Window...")
> >> except Exception:
> >> print (sys.exc_info()[1])
> >>
> >> Thanks, Jim
> >>
> >> _______________________________________________
> >> PySide mailing list
> >> PySide at qt-project.org
> >> http://lists.qt-project.org/mailman/listinfo/pyside
> >>
> >
> >
> >
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> >
>
>
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