如何显示PySide / PyQt UI并自动运行其中一种方法？

Question

I wish to open a PySide/PyQt window and automatically start executing a method, which will show a progress in the UI while it is executing.

With the code below, the ui is not shown until the process has completed, thus you cannot see the progress. How can I change the code to see the progress before the process has completed?

from PySide import QtGui
import time

class MyApp(QtGui.QMainWindow)
    def __init__(self, parent=None):
        super(MyApp, self).__init__(parent)

        # Setup
        self.centralWidget = QtGui.QWidget(self)
        self.setCentralWidget(self.centralWidget)
        self.setup_UI()

        # Execute process!
        self.process()

    def setup_UI(self):
        ''' Attach widgets to window '''
        self.mainLayout=QtGui.QVBoxLayout(self.centralWidget)
        self.list_widget = QtGui.QListWidget()
        self.progress_bar = QtGui.QProgressBar()
        self.mainLayout.addWidget(self.list_widget)
        self.mainLayout.addWidget(self.progress_bar)

    def process(self):
        ''' Manipulate the ui '''
        self.progress_bar.setMaximum(0)
        self.progress_bar.setMaximum(10)

        for x in range(0, 10):
            time.sleep(1)
            self.list_widget.addItem('Item ' + str(x))
            self.progress_bar.setValue(x)



my_app = MyApp()
my_app.show()

Answer 1

Your main problem that you are blocking qt main thread by calling time.sleep . To solve this issue you have two options. One of them is using threading . Another option is change your code to asynchronous like this:

from PySide import QtGui, QtCore
import time
import sys

class MyApp(QtGui.QMainWindow):
    def __init__(self, parent=None):
        super(MyApp, self).__init__(parent)

        # Setup
        self.centralWidget = QtGui.QWidget(self)
        self.setCentralWidget(self.centralWidget)
        self.setup_UI()

        # Execute process!
        self.set_process()
        self.timer = QtCore.QTimer()
        self.i = 0
        self.timer.timeout.connect(self.update)
        self.timer.start(1000)

    def setup_UI(self):
        ''' Attach widgets to window '''
        self.mainLayout=QtGui.QVBoxLayout(self.centralWidget)
        self.list_widget = QtGui.QListWidget()
        self.progress_bar = QtGui.QProgressBar()
        self.mainLayout.addWidget(self.list_widget)
        self.mainLayout.addWidget(self.progress_bar)

    def set_process(self):
        ''' Manipulate the ui '''
        self.progress_bar.setMaximum(0)
        self.progress_bar.setMaximum(10)

    def update(self):
        if self.i > 9:
            self.timer.stop()

        self.list_widget.addItem('Item ' + str(self.i))
        self.progress_bar.setValue(self.i)
        self.i += 1


def main():
    app = QtGui.QApplication(sys.argv)
    my_win = MyApp()
    my_win.show()
    sys.exit(app.exec_())


if __name__ == "__main__":
    main()

This example are using Qtimer object for updating progress bar with delay.

Answer 2

The example can be made to work quite easily by starting the processing with a single-shot timer and then calling processEvents within the loop to update the GUI:

    # Execute process!
    QtCore.QTimer.singleShot(100, self.process)

    ...

    for x in range(0, 10):
        time.sleep(1)
        ...
        QtGui.qApp.processEvents(QtCore.QEventLoop.AllEvents, 50)

However, there is no guarantee that this type of approach will work with a more realistic example. You may end up needing to use threads or multiprocessing - it all depends on the specific kind of processing you are going to do.