QML在PyQt5中的前端和后端分离
QML在PyQt5中的前端和后端分离
提问于 2019-03-22 09:12:54
我想将QML添加到一个已有的Python线程任务中，但我不知道如何不对任务进行过多的更改，以便将前端和后端分隔开来。
让我用一个最小的例子来解释这个问题。我希望使用QML添加GUI来控制进程(或线程)的启动和停止，以及获取和显示来自进程的信息。例如，下面是一些繁重工作的过程。
class Task(threading.Thread):
def __init__(self):
super().__init__()
self.num = 0
def run(self):
for i in range(35):
self.num = fib(i)
def fib(N):
if N <= 1:
return 1
return fib(N - 1) + fib(N - 2)现在，我尝试创建一个QML文件，以便在不阻塞self.num的情况下在Task中获得Task().start()。
import QtQuick 2.12
import QtQuick.Controls 2.12
ApplicationWindow {
visible: true
Column {
Button {
text: 'hello'
onClicked: {
backend.start_process()
}
}
Text {
text: backend.num
}
}
}为了保持前端和后端的分离，是否有任何方法将Task连接到QML而不更改Task中的任何脚本内容？根据这个问题，我尝试创建一个处理前端和后端之间任何通信的Backend类，并将上下文属性设置为QML (engine.rootContext().setContextProperty("backend", Backend()))。例如,
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()但是，我不知道如何在中双向绑定 self.num和t.num。因此，在QML中的按钮调用了t.num之后，我无法实时更新start_process()。
我希望最小化对Task的修改，因为它是旧程序的核心功能。因此，PyQt5网站中的简单示例不能满足我的要求。
此外，如果我想将Python更改为threading.Thread，那么在每次更新变量以在QML上显示变量时，我应该做什么来获得它呢？
回答 1
Stack Overflow用户
回答已采纳
发布于 2019-03-22 21:39:54
首先，您不需要像qproperty这样的setter，因为根据您的逻辑，您不应该修改QML中的qproperty。另一方面，您必须通过args或kwargs将后端传递给您的线程，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_())另一种方法是创建一个包含以下信息的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，它不再从threading.Thread继承，而是从实现向主线程发送信息的一些信号的QThread继承。
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_())页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/55296264
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