Waiting for a timer to terminate before continuing running the code

问题

The following code updates the text of a button every second after the START button was pressed. The intended functionality is for the code to 'wait' until the timer has stopped before continuing on with the execution of the code. That is, after START is pressed, the text of the second button is incremented to 3, and only then should the text I waited! appear on the console.


import sys
from PySide import QtGui, QtCore

class Example(QtGui.QWidget):

    def __init__(self, parent=None):
        super(Example, self).__init__(parent)

        self.app_layout = QtGui.QVBoxLayout()
        self.setLayout(self.app_layout)

        self.setGeometry(300, 300, 50, 50)

        self.current_count = 0

        self.count_to = 4
        self.delay = 1000

        self.timer = QtCore.QTimer(self)
        self.timer.timeout.connect(self.updateButtonCount) 

        # start button
        start_button = QtGui.QPushButton()
        start_button.setText('START')
        start_button.clicked.connect(self.startCount)
        self.app_layout.addWidget(start_button)

        # number button
        self.number_button = QtGui.QPushButton()
        self.number_button.setText('0')
        self.app_layout.addWidget(self.number_button)



    def updateButtonCount(self):
        self.number_button.setText("%s" % self.current_count)
        self.current_count += 1
        if self.current_count == self.count_to:
            self.timer.stop()


    def startCount(self):
        self.current_count = 0
        self.timer.start(self.delay)

        # this loop hangs the GUI:
        while True:
            if not self.timer.isActive():
                break

        print 'I waited!'


def main():

    app = QtGui.QApplication(sys.argv)
    example = Example()
    example.show()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

The above code hangs the GUI, and if I remove the while True: loop, the I waited! appears immidiately on the console.

I'm certain that the while True: loop is not the correct way to go about it, so I'm looking for suggestions.

回答1:

The solution I found that works was to replace

while True:
    if not self.timer.isActive():
        break

with

while self.timer.isActive():
    QtGui.QApplication.processEvents()

I'm not certain that this is the best solution, though.

来源：https://stackoverflow.com/questions/23867681/waiting-for-a-timer-to-terminate-before-continuing-running-the-code

标签

python

pyside