PyQt - Modify GUI from another thread

Question

I'm trying to modify my main layout from another thread. But the function run() is never called and i'm having the error:

QObject::setParent: Cannot set parent, new parent is in a different thread

Here's my code:

class FeedRetrievingThread(QtCore.QThread):
    def __init__(self, parent=None):
        super(FeedRetrievingThread, self).__init__(parent)
        self.mainLayout = parent.mainLayout
    def run(self):
        # Do things with self.mainLayout

class MainWindow(QtGui.QDialog):
    def __init__(self, parent=None):  
        super(MainWindow, self).__init__(parent)
        self.mainLayout = QtGui.QGridLayout() 
        self.setLayout(self.mainLayout)  
        self.feedRetrievingThread = FeedRetrievingThread(self)
        self.timer = QtCore.QTimer()
        self.timer.timeout.connect(self.updateFeed)
        self.timer.start(1000)

    def updateFeed(self):
        if not self.feedRetrievingThread.isRunning():
            print 'Running thread.'
            self.feedRetrievingThread.start()

if __name__ == '__main__':  
    app = QtGui.QApplication(sys.argv)  
    mainWindow = MainWindow()  
    mainWindow.show()
    sys.exit(app.exec_())

I really don't get it, why is it so difficult to access the GUI with PyQt? In C# you have Invoke. Is there anything of the kind in PyQt?

I tried creating the thread directly from MainWindow.__init__ (without using the timer) but it didn't work either.

Answer 1

In Qt you should never attempt to directly update the GUI from outside of the GUI thread.

Instead, have your threads emit signals and connect them to slots which do the necessary updating from within the GUI thread.

See the Qt documentation regarding Threads and QObjects.