How to make a qml object's property “dynamical

Question

I am using PyQt5 and Qml to create a client application. This is a simplified sample of my Qml file:

import QtQuick 2.11
import QtQuick.Window 2.2
import QtQuick.Controls 2.2

ApplicationWindow {    
    visible: true
    width: Screen.width/2
    height: Screen.height/2
    Rectangle {
        id: rectangle
        x: 187
        y: 92
        width: 200
        height: 200
        color: "blue"
    }
}

The client app must receive the properties of the above rectangle from the server. In order to do that, I implemented a socket connection in the ".py" file. the client.py file ought to receive information in real-time from the server. I was inspired by chat application programs and I used a (while True:{}) loop to do this:

from PyQt5.QtQml import QQmlApplicationEngine, QQmlProperty
from PyQt5.QtQuick import QQuickWindow, QQuickView
from PyQt5.QtCore import QObject, QUrl
from PyQt5.QtWidgets import QApplication
import sys, socket

    def run():
    myApp = QApplication(sys.argv)
    myEngine = QQmlApplicationEngine()

    myEngine.load('mainViewofHoomanApp.qml')
    Win = myEngine.rootObjects()[0]
    rect = Win.findChild(QObject, "rectangle")
    rect.setProperty("height", 10)  # Here I am accessing the properties of the rectangle
    if not myEngine.rootObjects():
        return -1
    return myApp.exec_()


if __name__ == "__main__":
    sys.exit(run())

And it is the format of socket connection:

client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
Server_IPAddress = '192.168.1.163'
Port = 5000
client_socket.connect((Server_IPAddress,Port))
while True:
    message = client_socket.recv(1024)

    # Then the code extracts the parameters from the message
    # and converts it to integer, and saves it in realT_width variable:

    rect.setProperty("height", realT_width variable)

I am confused about how to merge these two codes together. If I call the socket connection after write the myApp.exec_() command, then the QML file will no longer react to the parameter change commands. On the other hand, if I write the socket connection before the QML execution, then the while loop will not allow the latter code lines to be executed.

Answer 1

The blocking tasks must be executed in another thread so that they do not freeze the GUI, in this case I will assume that the next one is the server so you must launch it first.

server.py

import socket
import time
import random

HOST = '127.0.0.1'
PORT = 65432

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
    s.bind((HOST, PORT))
    s.listen()
    conn, addr = s.accept()
    with conn:
        print('Connected by', addr)
        while True:
            v = random.randint(10, 100)
            conn.sendall(str(v).encode())
            time.sleep(1.)

So I will create a QObject where I can create the signals that will send the information obtained by the socket that runs on a secondary thread to the handler that I publish in my other answer.

client.py

import os
import sys
import threading
import socket
from PyQt5 import QtCore, QtGui, QtQml
from functools import partial

class SocketWorker(QtCore.QObject):
    heightChanged = QtCore.pyqtSignal(float)

    @QtCore.pyqtSlot()
    def process(self):
        HOST = '127.0.0.1'  # The server's hostname or IP address
        PORT = 65432        # The port used by the server
        with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
            s.connect((HOST, PORT))
            while True:
                data = s.recv(1024)
                print('Received', repr(data))
                try:
                    height = float(data)
                    self.heightChanged.emit(height)
                except ValueError:
                    print("error")

class RectangleManager(QtCore.QObject):
    widthChanged = QtCore.pyqtSignal(float)
    heightChanged = QtCore.pyqtSignal(float)

    def __init__(self, parent=None):
        super(RectangleManager, self).__init__(parent)
        self._width = 100
        self._height = 100

    def getWidth(self):
        return self._width

    def setWidth(self, w):
        if self._width != w:
            self._width = w
            self.widthChanged.emit(w)

    def getHeight(self):
        return self._height

    def setHeight(self, h):
        if self._height != h:
            self._height = h
            self.heightChanged.emit(h)

    width = QtCore.pyqtProperty(float, fget=getWidth, fset=setWidth, notify=widthChanged)
    height = QtCore.pyqtProperty(float, fget=getHeight, fset=setHeight, notify=heightChanged)

def run():
    myApp = QtGui.QGuiApplication(sys.argv)
    myEngine = QtQml.QQmlApplicationEngine()
    manager = RectangleManager()
    myEngine.rootContext().setContextProperty("r_manager", manager)
    directory = os.path.dirname(os.path.abspath(__file__))
    myEngine.load(QtCore.QUrl.fromLocalFile(os.path.join(directory, 'main.qml')))

    if not myEngine.rootObjects():
        return -1

    worker = SocketWorker()
    threading.Thread(target=worker.process, daemon=True).start()
    worker.heightChanged.connect(manager.setHeight)
    return myApp.exec_()

if __name__ == "__main__":
    sys.exit(run())

---

main.qml

import QtQuick 2.11
import QtQuick.Window 2.2
import QtQuick.Controls 2.2

ApplicationWindow {    
    visible: true
    width: Screen.width/2
    height: Screen.height/2
    Rectangle {
        id: rectangle
        x: 187
        y: 92
        width: r_manager.width
        height: r_manager.height
        color: "blue"
    }
}