PyQt - how to detect and close UI if it's already running?

Question

I\'m starting the UI from within Maya. If the UI hasn\'t been closed, running the UI again will completely freeze Maya (with the error \"Event Loop is already running\")

Answer 1

My solution is this:

import sys

from PyQt5.QtCore import QLockFile
from PyQt5.QtWidgets import QApplication
from PyQt5.QtWidgets import QMessageBox

from window import MainWindow


if __name__ == "__main__":
    try:
        app_object = QApplication(sys.argv)
        lock_file = QLockFile("app.lock")

        if lock_file.tryLock():
            window = MainWindow()
            window.show()

            app_object.exec()
        else:
            error_message = QMessageBox()
            error_message.setIcon(QMessageBox.Warning)
            error_message.setWindowTitle("Error")
            error_message.setText("The application is already running!")
            error_message.setStandardButtons(QMessageBox.Ok)
            error_message.exec()
    finally:
        lock_file.unlock()