CODEWITHSUNDEEP
pythonmultithreading
Keni Mardira
Keni Mardira

Reputation: 25

PyQt5 QThread passing variables to main

I am trying to make a GUI which will interact with a serial device.

As of right now, I have successfully made a very simple GUI which can open and close the serial connection.

Below is my code:

import sys
from PyQt5.QtCore import *

from PyQt5.QtWidgets import QMainWindow, QApplication, QWidget, QMessageBox,      QAction, qApp, QPushButton

from PyQt5.QtGui import QIcon

import serial

ser = serial.Serial()
ser.baudrate = 115200
ser.port = 2

class MainUI(QMainWindow):

def __init__(self):
    super().__init__()
    self.initUI()
    self.workerThread = SerialRead()
    self.connect(self.workerThread, QtCore.SIGNAL("mysignal(QString)"),self.on_change, QtCore.Qt.QueuedConnection)

def initUI(self):
    btn1 = QPushButton('Open Serial', self)
    btn1.clicked.connect(self.openSerial)
    btn1.resize(btn1.sizeHint())
    btn1.move(50,50)

    btn2 = QPushButton('Close Serial', self)
    btn2.clicked.connect(self.closeSerial)
    btn2.resize(btn2.sizeHint())
    btn2.move(50,100)

    exitAction = QAction(QIcon('exit.png'), '&Exit', self)
    exitAction.setShortcut('Alt+F4')
    exitAction.setStatusTip('Exit application')
    exitAction.triggered.connect(self.closeEvent)

    self.statusBar()
    menubar = self.menuBar()
    fileMenu = menubar.addMenu('&File')
    fileMenu.addAction(exitAction)

    self.statusBar().showMessage('Ready')
    self.setGeometry(300,300,250,150)
    self.setWindowTitle('Motor Driver')

    self.show()

def openSerial(self):
    ser.open()
    self.workerThread.start()

def closeSerial(self):
    ser.close()
    self.workerThread.terminate()

def closeEvent(self, event):
    reply = QMessageBox.question(self, 'Message', "Are you sure you want to quit?", QMessageBox.Yes | QMessageBox.No, QMessageBox.No)
    if reply == QMessageBox.Yes:
        event.accept()
    else:
        event.ignore()

class SerialRead(QThread):
def __init__(self):
    super().__init__()
    self.data = []

def run(self):
    while True:
        x = ser.readline()
        # if x != b'\n':
        #   self.data.append(str(x))
        # else:
        self.emit(QtCore.SIGNAL("mysignal(Qstring)"), (x.decode("utf-8")))
            # self.data = []



if __name__ == '__main__':
app = QApplication(sys.argv)
main = MainUI()
sys.exit(app.exec_())

My question would be on how to pass a variable from my serialRead thread to my MainUI? As you can see on my code, I have tried the solutions which I can found online, which is by using:

self.connect(self.workerThread, QtCore.SIGNAL("mysignal(QString)"),self.on_change, QtCore.Qt.QueuedConnection)

on my MainUI class and by using:

self.emit(QtCore.SIGNAL("mysignal(Qstring)"), (x.decode("utf-8")))

on my thread.

However, this gives me this error: 'MainUI' object has no attribute 'connect'

So how should I pass a variable from my thread to my MainUI?

It has been almost 2 years since I last touched python and I just started this project about 2 days ago, but is there anyway I can improve my code? Are there any subtle or obvious errors that I made?

Upvotes: 2

Views: 5522

Answers (1)

Mel
Mel

Reputation: 6065

On PyQt5, you have to use the new style signal and slot

self.workerThread.mySignal.connect(self.on_change)

class SerialRead(QThread):
    mySignal = pyqtSignal(str) 

    def __init__(self):    
        super().__init__()

    def run(self):
        self.mySignal.emit(some_string)

Upvotes: 5

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