PyQt QThread多线程不起作用

Question

I have 2 QListWidget lists, List2 is being filled when some item has been selected from List1

The problem is that, before filling List2 i have to do alot of tasks which freezes my UI for about 5 seconds which is too annoying, i want to make it fill List2 with QThread but it's not working since before initilizing whole class I'm getting an annoying error

from ui import Ui_Win
from PyQt4 import QtGui, QtCore

class GenericThread(QtCore.QThread):
    def __init__(self, parent=None):
        QtCore.QThread.__init__(self, parent)

    def __del__(self):
        self.quit()
        self.wait()

    def run(self):
        self.emit( QtCore.SIGNAL('itemSelectionChanged()'))
        return

class MainUI(QtGui.QMainWindow):
    def __init__(self, parent=None):
        QtGui.QMainWindow.__init__(self)
        self.ui = Ui_Win()
        self.ui.setupUi(self)
        ...

        genericThread = GenericThread(self)
        self.connect(genericThread, QtCore.SIGNAL("itemSelectionChanged()"), self.fill_List2 )
        genericThread.start()

    def fill_List2(self):
        self.ui.List2.clear()
        list1SelectedItem = str(self.ui.List1.currentItem().text()) # ERROR HERE

Traceback: # AttributeError: 'NoneType' object has no attribute 'text'

This accures because self.ui.List1.currentItem().text() is None

Why this fucntion is being called before triggering itemSelectionChanged signal?

Answer 1

from ui import Ui_Win ## ui.py is a file that has been generated from Qt Designer and it contains main GUI objects like QListWidget
from PyQt4 import QtGui, QtCore

class GenericThread(QtCore.QThread):
    def __init__(self, parent=None, listIndex=0):
        QtCore.QThread.__init__(self, parent)
        self.listIndex = listIndex

    def __del__(self):
        self.quit()
        self.wait()

    def run(self):
        if self.listIndex == 2:
            for addStr in Something:
                #Some long stuff
                self.emit( QtCore.SIGNAL('fillListWithItems(QString, int'), addStr, self.listIndex)

class MainUI(QtGui.QMainWindow):
    def __init__(self, parent=None):
        QtGui.QMainWindow.__init__(self)
        self.ui = Ui_Win()
        self.ui.setupUi(self)
        ...

        self.ui.List1.list1SelectedItem.connect(self.fill_List2)

    @QtCore.pyqtSlot(QString, int)
    def self.fillListWithItems(addStr, lstIdx):
        if lstIdx==2:
            self.ui.List2.addItem(addStr)

    def fill_List2(self):
        self.ui.List2.clear()
        list1SelectedItem = str(self.ui.List1.currentItem().text())

        genericThread = GenericThread(self, listIndex=2)
        self.connect(genericThread, QtCore.SIGNAL("fillListWithItems(QString, int)"), self.fillListWithItems )
        genericThread.start()

Thanks @ekhumoro

Answer 2

Your problem is that simply starting the thread is firing the itemSelectionChanged() signal (because it is in the run function), which you have connected to your fill_List2() function. You need to connect the itemSelectionChanged event on List1 to a SLOT that will trigger the thread to do the heavy computation and update List2 .

I've had to make a number of assumptions about what ui is and what List1 and List2 are and how they're set up, but here is a working example. I've replaced the heavy computation in your GenericThread with a simple 2 second delay.

If I've misinterpreted / made bad assumptions, please update the question and leave a comment

test_slotting.py

from ui import Ui_Win
from PyQt4 import QtGui, QtCore
from PyQt4.QtCore import pyqtSlot
from PyQt4.QtGui import *
import time

class GenericThread(QtCore.QThread):
    def __init__(self, parent=None):
        QtCore.QThread.__init__(self, parent)

    def __del__(self):
        self.quit()
        self.wait()

    def run(self):
        #Do all your heavy processing here
        #I'll just wait for 2 seconds
        time.sleep(2)
        self.emit( QtCore.SIGNAL('itemSelectionChanged()'))
        return

class MainUI(QtGui.QMainWindow):
    def __init__(self, parent=None):
        QtGui.QMainWindow.__init__(self)
        self.ui = Ui_Win()
        self.ui.setupUi(self)
        self.ui.List1 = QListWidget(self)
        self.ui.List2 = QListWidget(self)

        hbox = QtGui.QHBoxLayout()
        hbox.addStretch(1)
        hbox.addWidget(self.ui.List1)
        hbox.addWidget(self.ui.List2)

        self.ui.centralWidget.setLayout(hbox)

        self.ui.List1.addItems(['alpha','beta','gamma','delta','epsilon'])
        self.ui.List2.addItems(['Item1','Item2'])

        self.ui.List1.itemSelectionChanged.connect(self.start_heavy_processing_thread)

    @pyqtSlot()
    def start_heavy_processing_thread(self):
        genericThread = GenericThread(self)
        self.connect(genericThread, QtCore.SIGNAL("itemSelectionChanged()"), self.fill_List2 )
        genericThread.start()

    def fill_List2(self):
        self.ui.List2.clear()
        list1SelectedItem = str(self.ui.List1.currentItem().text())
        self.ui.List2.addItem(list1SelectedItem)

if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)
    MainWindow = MainUI()
    MainWindow.show()
    sys.exit(app.exec_())

ui.py

from PyQt4 import QtCore, QtGui

class Ui_Win(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(416, 292)
        self.centralWidget = QtGui.QWidget(MainWindow)
        self.centralWidget.setObjectName("centralWidget")
        MainWindow.setCentralWidget(self.centralWidget)

if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)
    MainWindow = QtGui.QMainWindow()
    ui = Ui_Win()
    ui.setupUi(MainWindow)
    MainWindow.show()
    sys.exit(app.exec_())