使用QML在PyQt5中进行前端和后端分离

Question

我想将QML UI添加到一个现有的Python线程任务中，但是我不知道如何做得太多而又不改变任务以保持前端和后端分离。

让我用一个最小化的例子来解释这个问题。我想添加带有QML的GUI来控制进程（或线程）的启动和停止以及获取和显示进程信息。例如，以下是一些繁重的工作。

self.num

现在，我尝试创建一个QML文件，以在Task之后获得Task().start()中的import QtQuick 2.12 import QtQuick.Controls 2.12 ApplicationWindow { visible: true Column { Button { text: 'hello' onClicked: { backend.start_process() } } Text { text: backend.num } } } ，而不会阻塞。

Task

为了保持前端和后端分离，是否有任何方法可以将Task连接到QML UI，而无需更改Backend中的任何脚本内容？根据{{​​3}}，我尝试创建一个engine.rootContext().setContextProperty("backend", Backend())类来处理前端和后端之间的任何通信，并将context属性设置为QML（class Backend(PyQt5.QtCore.QObject): changed = PyQt5.QtCore.pyqtSignal(int) def __init__(self): super().__init__() self._num = 0 @PyQt5.QtCore.pyqtProperty(int, notify=changed) def num(self): return self._num @num.setter def num(self, val): if self._num == val: return self._num = val self.changed.emit(self._num) @PyQt5.QtCore.pyqtSlot() def start_process(self): t = Task() t.start() ）。例如，

self.num

但是，我不知道如何双向绑定 t.num中的backend和t.num。因此，在QML UI中的按钮调用start_process()之后，我无法实时更新Task。

我想最小化threading.Thread的修改，因为它是旧程序的核心功能。因此，this question无法满足我的要求。

此外，如果我想将Python multiprocessing.Process更改为{{1}}，我应该怎么做才能在每次更新过程中获取变量以便在QML UI上显示？

Answer 1

首先，您不需要像qproperty这样的设置器，因为根据您的逻辑，您不应从QML修改qproperty。另一方面，您必须通过args或kwargs将后端传递给线程，并发送调用插槽的信息：

import threading
import time
from PyQt5 import QtCore, QtGui, QtQml

class Task(threading.Thread):
    def run(self):
        self.backend = self._kwargs.get('backend')
        for i in range(35):
            num = fib(i)
            if self.backend is not None:
                QtCore.QMetaObject.invokeMethod(
                    self.backend, 
                    "set_num",
                    QtCore.Qt.QueuedConnection, 
                    QtCore.Q_ARG(int, num)
                )
                time.sleep(0.01)
def fib(N):
    if N <= 1:
        return 1
    return fib(N - 1) + fib(N - 2)

class Backend(QtCore.QObject):
    changed = QtCore.pyqtSignal(int)

    def __init__(self):
        super().__init__()
        self._num = 0

    @QtCore.pyqtProperty(int, notify=changed)
    def num(self):
        return self._num

    @QtCore.pyqtSlot(int)
    def set_num(self, val):
        if self._num == val:
            return
        self._num = val
        self.changed.emit(self._num)

    @QtCore.pyqtSlot()
    def start_process(self):
        Task(kwargs=dict(backend=self), daemon=True).start()

if __name__ == "__main__":
    import os
    import sys

    app = QtGui.QGuiApplication(sys.argv)
    backend = Backend()
    engine = QtQml.QQmlApplicationEngine()
    engine.rootContext().setContextProperty("backend", backend)
    qml_path = os.path.join(os.path.dirname(__file__), "main.qml")
    engine.load(QtCore.QUrl.fromLocalFile(qml_path))
    if not engine.rootObjects():
        sys.exit(-1)
    engine.quit.connect(app.quit)
    sys.exit(app.exec_())

---

另一种方法是创建具有以下信息的QEvent：

import threading
import time
from PyQt5 import QtCore, QtGui, QtQml

class InfoEvent(QtCore.QEvent):
    EventType = QtCore.QEvent.User

    def __init__(self, info):
        super(InfoEvent, self).__init__(InfoEvent.EventType)
        self._info = info

    @property
    def info(self):
        return self._info

class Task(threading.Thread):
    def run(self):
        self.backend = self._kwargs.get('backend')
        for i in range(35):
            num = fib(i)
            if self.backend is not None:
                event = InfoEvent(num)
                QtCore.QCoreApplication.sendEvent(self.backend, event)
                time.sleep(0.01)
def fib(N):
    if N <= 1:
        return 1
    return fib(N - 1) + fib(N - 2)

class Backend(QtCore.QObject):
    changed = QtCore.pyqtSignal(int)

    def __init__(self):
        super().__init__()
        self._num = 0

    def event(self, e):
        if e.type() == InfoEvent.EventType:
            self.set_num(e.info)
            return True
        return super(Backend, self).event(e)

    @QtCore.pyqtProperty(int, notify=changed)
    def num(self):
        return self._num

    @QtCore.pyqtSlot(int)
    def set_num(self, val):
        if self._num == val:
            return
        self._num = val
        self.changed.emit(self._num)

    @QtCore.pyqtSlot()
    def start_process(self):
        Task(kwargs=dict(backend=self), daemon=True).start()

if __name__ == "__main__":
    import os
    import sys

    app = QtGui.QGuiApplication(sys.argv)
    backend = Backend()
    engine = QtQml.QQmlApplicationEngine()
    engine.rootContext().setContextProperty("backend", backend)
    qml_path = os.path.join(os.path.dirname(__file__), "main.qml")
    engine.load(QtCore.QUrl.fromLocalFile(qml_path))
    if not engine.rootObjects():
        sys.exit(-1)
    engine.quit.connect(app.quit)
    sys.exit(app.exec_())

---

另一种解决方案是它不再继承自threading.Thread，而是继承自QThread，后者实现了一些将信息发送到主线程的信号。

from PyQt5 import QtCore, QtGui, QtQml

class Task(QtCore.QThread):
    valueChanged = QtCore.pyqtSignal(int)

    def run(self):
        for i in range(35):
            num = fib(i)
            self.valueChanged.emit(num)
            QtCore.QThread.msleep(1)

def fib(N):
    if N <= 1:
        return 1
    return fib(N - 1) + fib(N - 2)

class Backend(QtCore.QObject):
    changed = QtCore.pyqtSignal(int)

    def __init__(self):
        super().__init__()
        self._num = 0

    @QtCore.pyqtProperty(int, notify=changed)
    def num(self):
        return self._num

    @QtCore.pyqtSlot(int)
    def set_num(self, val):
        if self._num == val:
            return
        self._num = val
        self.changed.emit(self._num)

    @QtCore.pyqtSlot()
    def start_process(self):
        thread = Task(self)
        thread.valueChanged.connect(self.set_num)
        thread.start()

if __name__ == "__main__":
    import os
    import sys

    app = QtGui.QGuiApplication(sys.argv)
    backend = Backend()
    engine = QtQml.QQmlApplicationEngine()
    engine.rootContext().setContextProperty("backend", backend)
    qml_path = os.path.join(os.path.dirname(__file__), "main.qml")
    engine.load(QtCore.QUrl.fromLocalFile(qml_path))
    if not engine.rootObjects():
        sys.exit(-1)
    engine.quit.connect(app.quit)
    sys.exit(app.exec_())