Recreate QApplication after previous instance has been exited

Question

Is is possible to create and use new QApplication instance after previous one has been exited?

Did you try with simple case ? I did and I am definitely able to do so. I use this to run test apps successively ... So I would say, yes. — Thomas Vincent, Jul 21 '11 at 15:24

Judge Maygarden · Answer 1 · 2011-07-21T19:57:06.140

4

Yes, you can create a new QApplication after the previous instance is destroyed. I verified this in Windows using PyQt4. The program below displays an empty windows. Upon closing the first window the first QApplication is destroyed and a second QApplication is created that then shows a second blank window. Note that I had problems without the del app statement. This would be equivalent to using delete on your QApplication in C++. Just make sure to allocate the QApplication instance on the heap instead of the stack.

from PyQt4 import QtCore, QtGui
import sys

app = QtGui.QApplication(sys.argv)
window = QtGui.QWidget()
window.show()
app.exec_()
del app # force garbage collection of the first QApplication

app = QtGui.QApplication(sys.argv)
window = QtGui.QWidget()
window.show()
app.exec_()

edited Jul 21 '11 at 19:57

answered Jul 21 '11 at 15:53

Judge Maygarden

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Is there a way I can render multiople URLs like this? http://blog.sitescraper.net/2010/06/scraping-javascript-webpages-in-python.html – Shane Reustle Aug 04 '11 at 20:39
That's a bit off topic. However, there is no need for multiple QApplication instances. Just create multiple web views. – Judge Maygarden Aug 05 '11 at 14:16

score 0 · Answer 2 · edited May 23 '17 at 12:06

0

Looks like this question discusses that:

Problems with Multiple QApplications

Instead of creating a new instance of QApplication, you could create a new thread with its own window, and treat that as you would of a different QApplication from within the single program.

edited May 23 '17 at 12:06

Community

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answered Jul 21 '11 at 15:25

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I believe the other question has a subtle difference. It sounds like mgamer wants to only have one QApplication active at a time, but create a new one after the previous one is destroyed. – Judge Maygarden Jul 21 '11 at 15:30
@Judge Maygarden - that is exactly what I try to achieve – mgamer Jul 21 '11 at 15:40

score 0 · Answer 3 · answered May 28 '23 at 09:15

For who google for Python, This is worked with me fine

if __name__ == "__main__":
    # Create a singleinstance of QApplication
    app = QApplication.instance()
    if not app:
        app = QApplication(sys.argv)
    window = MainWindow()
    window.show()
    sys.exit(app.exec())

Recreate QApplication after previous instance has been exited

3 Answers3