QObject: Cannot create children for a parent that is in a different thread. PyQt5

Question

When I try to change the text of a text browser which is inside a scroll area I get this PyQt5 threading error:

QObject: Cannot create children for a parent that is in a different thread.
(Parent is QTextDocument(0x212e3bb1f50), parent's thread is QThread(0x212e171e220), current thread is QThread(0x212e41dc7e0)

I assume it is because of the scroll area and that I don't have access to it from the thread I am trying to change this from and it works if I put the same bit of code...

filepath = "..."
with open(filepath, "r") as f:
    contents = f.read()
    #print(contents)
    self.log_1.setText(contents)

(and yes I am aware that the filepath is "...", used for file security.)...inside the thread that the scrollarea is created inside it works completely fine.

The only thing I don't know is how to fix this. I think you might be able to inherit the thread to the scroll area in someway, idk.

My code, but simplified:

from PyQt5 import QtCore, QtGui, QtWidgets
from mcstatus import MinecraftServer
import threading

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(1379, 523)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.scrollArea_1 = QtWidgets.QScrollArea(self.S1)
        self.scrollArea_1.setGeometry(QtCore.QRect(0, 20, 981, 341))
        self.scrollArea_1.setWidgetResizable(True)
        self.scrollArea_1.setObjectName("scrollArea_1")
        self.scrollAreaWidgetContents_1 = QtWidgets.QWidget()
        self.scrollAreaWidgetContents_1.setGeometry(QtCore.QRect(0, 0, 979, 339))
        self.scrollAreaWidgetContents_1.setObjectName("scrollAreaWidgetContents_1")
        self.log_1 = QtWidgets.QTextBrowser(self.scrollAreaWidgetContents_1)
        self.log_1.setGeometry(QtCore.QRect(0, 0, 981, 341))
        self.log_1.setMinimumSize(QtCore.QSize(981, 341))
        self.log_1.viewport().setProperty("cursor", 
        QtGui.QCursor(QtCore.Qt.IBeamCursor))
        self.log_1.setObjectName("log_1")
        self.scrollArea_1.setWidget(self.scrollAreaWidgetContents_1)

    def update1(self, MainWindow):

        threading.Timer(0.2, self.update1, {MainWindow: MainWindow}).start()

        ip = "..."
        port = 25565 #Server 1
        server = MinecraftServer(ip, port)

        try:



            filepath = "..."
            with open(filepath, "r") as f:
                contents = f.read()
                #print(contents)
                self.log_1.setText(contents)



        except IOError as e:

            self.StatusL_1.setText(self.translate("MainWindow", "<html><head/><body><p><span style=\" font-size:18pt;\">Status: Off</span></p></body></html>"))
        else:
            self.StatusL_1.setText(self.translate("MainWindow", "<html><head/><body><p><span style=\" font-size:18pt;\">Status: On</span></p></body></html>"))

Answer 1

You should not directly modify the GUI from another thread, one way to modify the GUI indirectly from another thread is to use the Qt signals:

import threading
from PyQt5 import QtCore, QtGui, QtWidgets
from mcstatus import MinecraftServer


class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        # ...


class Worker(QtCore.QObject):
    logged = QtCore.pyqtSignal(str)
    statusChanged = QtCore.pyqtSignal(bool)

    def start(self):
        threading.Timer(0.2, self._execute, daemon=True).start()

    def _execute(self):
        threading.Timer(0.2, self._execute, daemon=True).start()
        ip = "..."
        port = 25565  # Server 1
        server = MinecraftServer(ip, port)

        try:
            filepath = "..."
            with open(filepath, "r") as f:
                contents = f.read()
                self.logged.emit(contents)
        except IOError as e:
            self.statusChanged.emit(False)
        else:
            self.statusChanged.emit(True)


class MainWindow(QtWidgets.QMainWindow, Ui_MainWindow):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.setupUi(self)

        self.worker = Worker()
        self.worker.logged.connect(self.log_1.setText)
        self.worker.statusChanged.connect(self.on_status_changed)
        self.worker.start()

    @QtCore.pyqtSlot(bool)
    def on_status_changed(self, status):
        text = '<html><head/><body><p><span style=" font-size:18pt;">Status: {}</span></p></body></html>'.format(
            "On" if status else "Off"
        )
        self.StatusL_1.setText(text)


if __name__ == "__main__":
    import sys

    app = QtWidgets.QApplication(sys.argv)
    w = MainWindow()
    w.show()
    sys.exit(app.exec_())

QObject: Cannot create children for a parent that is in a different thread. PyQt5

Question

1 answers

solution1
1 ACCPTED 2020-05-16 20:36:44

QObject: Cannot create children for a parent that is in a different thread. PyQt5

Question

1 answers

solution1 1 ACCPTED 2020-05-16 20:36:44

solution1
1 ACCPTED 2020-05-16 20:36:44