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PyQt子線(xiàn)程處理業(yè)務(wù)事件的問(wèn)題解決

更新時(shí)間：2024年02月07日 09:42:38 作者：阮靚仔

在PyQt中,主線(xiàn)程通常是指GUI主循環(huán)所在的線(xiàn)程,而子線(xiàn)程則是執(zhí)行實(shí)際工作的線(xiàn)程,本文主要介紹了PyQt子線(xiàn)程處理業(yè)務(wù)事件的問(wèn)題解決,具有一定的參考價(jià)值,感興趣的可以了解一下

在PyQt中是不推薦使用UI主線(xiàn)程來(lái)處理耗時(shí)操作的，會(huì)造成窗口組件阻塞。耗時(shí)操作一般放在子線(xiàn)程中。子線(xiàn)程處理完成后，可能需要更新窗口組件，但是PyQt不推薦使用子線(xiàn)程來(lái)更新主線(xiàn)程（也不是不能更新），這就用到了信號(hào)槽機(jī)制來(lái)更新主線(xiàn)程。

在QObject的一個(gè)子類(lèi)中創(chuàng)建一個(gè)信號(hào)（PyQt5.QtCore.pyqtSignal）屬性
將這個(gè)信號(hào)屬性和其他類(lèi)中的函數(shù)綁定，綁定的這個(gè)函數(shù)叫做整個(gè)信號(hào)的槽函數(shù)。一個(gè)信號(hào)可以和多個(gè)槽函數(shù)綁定。
該信號(hào)發(fā)出時(shí)，就會(huì)調(diào)用對(duì)應(yīng)的槽函數(shù)

可能會(huì)有疑問(wèn)，槽函數(shù)被執(zhí)行時(shí)所在的線(xiàn)程和發(fā)送信號(hào)的線(xiàn)程是不是同一個(gè)？

需要注意，信號(hào)一定義在QObject或其子類(lèi)中。調(diào)用該屬性的emit方法發(fā)出信號(hào)后，和該信號(hào)綁定的槽函數(shù)都將要被調(diào)用，但是調(diào)用的線(xiàn)程并不一定是發(fā)送信號(hào)的這個(gè)線(xiàn)程，這和PyQt中的線(xiàn)程親和性（Thread Affinity）有關(guān)。

線(xiàn)程親和性（Thread Affinity）

在 PyQt 中，一個(gè)對(duì)象可以被移動(dòng)到不同的線(xiàn)程中，但一個(gè)對(duì)象在同一時(shí)刻只能屬于一個(gè)線(xiàn)程。這是因?yàn)?Qt 使用線(xiàn)程親和性（Thread Affinity）的概念來(lái)管理對(duì)象所屬的線(xiàn)程。

每個(gè) Qt 對(duì)象都與一個(gè)特定的線(xiàn)程相關(guān)聯(lián)，即它的線(xiàn)程親和性。對(duì)象的線(xiàn)程親和性決定了該對(duì)象的槽函數(shù)是在哪個(gè)線(xiàn)程中執(zhí)行。默認(rèn)情況下，對(duì)象在創(chuàng)建時(shí)會(huì)與創(chuàng)建它的線(xiàn)程相關(guān)聯(lián)，但可以使用 moveToThread 方法將對(duì)象移動(dòng)到另一個(gè)線(xiàn)程中。

錯(cuò)誤示例：

from PyQt5.QtWidgets import QApplication, QMainWindow, QPushButton,QFileDialog
from PyQt5.QtCore import QThread,pyqtSignal,QObject
import sys, threading

class MyWindow(QMainWindow):
    def __init__(self, parent=None):
        super(MyWindow, self).__init__(parent)
        self.button = QPushButton('Hi')
        self.button.clicked.connect(self.on_click)
        self.setCentralWidget(self.button)

    def on_click(self):
        print("on_click",threading.current_thread().name)
        self.thread = MyThread(self)
        self.thread.start()

    def set_text(self,file_name):
        print("setText",threading.current_thread().name)
        self.button.setText(file_name)

class MyThread(QThread):

    def __init__(self,mv:QMainWindow) -> None:
        super().__init__(None)
        self.mv = mv
        
    def run(self):
        print('run',threading.current_thread().name)
        QThread.sleep(5)
        self.mv.set_text("Hello World")

if __name__ == '__main__':
    app = QApplication([])
    window = MyWindow()
    window.show()
    sys.exit(app.exec_())

輸出結(jié)果：

on_click MainThread
run Dummy-1
setText Dummy-1 //子線(xiàn)程更新UI，不推薦

使用信號(hào)槽機(jī)制

from PyQt5.QtWidgets import QApplication, QMainWindow, QPushButton,QFileDialog
from PyQt5.QtCore import QThread,pyqtSignal,QObject
import sys, threading
class MyWindow(QMainWindow):
    def __init__(self, parent=None):
        super(MyWindow, self).__init__(parent)
        self.button = QPushButton('Hi')
        self.button.clicked.connect(self.on_click)
        self.setCentralWidget(self.button)

    def on_click(self):
        print("on_click",threading.current_thread().name)
        self.thread = MyThread(self)
        self.thread.pyqtSignal.connect(self.set_text)
        self.thread.start()

    def set_text(self,file_name):
        print("setText",threading.current_thread().name)
        self.button.setText(file_name)

class MyThread(QThread):
    pyqtSignal =  pyqtSignal(str)
    def __init__(self,mv:QMainWindow) -> None:
        super().__init__(None)
        self.mv = mv

    def run(self):
        print('run',threading.current_thread().name)
        QThread.sleep(5)
        self.pyqtSignal.emit("Hello World")

if __name__ == '__main__':
    app = QApplication([])
    window = MyWindow()
    window.show()
    sys.exit(app.exec_())

輸出結(jié)果：

on_click MainThread
run Dummy-1
setText MainThread //更新UI時(shí)，執(zhí)行的線(xiàn)程為主線(xiàn)程

setText槽函數(shù)為什么會(huì)被主函數(shù)執(zhí)行，就是因?yàn)榫€(xiàn)程親和性，槽函數(shù)所在對(duì)象和MainThread綁定，當(dāng)然會(huì)被主線(xiàn)程所執(zhí)行。

但是這種將事務(wù)直接寫(xiě)在run，PyQt5是不推薦的，正確寫(xiě)法如下

創(chuàng)建一個(gè)類(lèi)集成QObject，來(lái)做業(yè)務(wù)的處理。并將這個(gè)對(duì)象和新創(chuàng)建的線(xiàn)程通過(guò)moveToThread綁定，作為這個(gè)對(duì)象的親和線(xiàn)程。將QThread的started信號(hào)和這個(gè)業(yè)務(wù)事件綁定。線(xiàn)程啟動(dòng)，發(fā)送started信號(hào)，業(yè)務(wù)對(duì)象開(kāi)始處理業(yè)務(wù)，完成之后發(fā)送信號(hào)給主線(xiàn)程槽函數(shù)。

from PyQt5.QtWidgets import QApplication, QMainWindow, QPushButton,QFileDialog
from PyQt5.QtCore import QThread,pyqtSignal,QObject
import sys, threading
class MyWindow(QMainWindow):
    def __init__(self, parent=None):
        super(MyWindow, self).__init__(parent)
        self.button = QPushButton('Hi')
        self.button.clicked.connect(self.on_click)
        self.setCentralWidget(self.button)

    def on_click(self):
        print("on_click",threading.current_thread().name)
        self.thread = QThread()

        self.myHander = MyHandler()
        self.myHander.moveToThread(self.thread)
        self.myHander.pyqtSignal.connect(self.set_text)

        self.thread.started.connect(self.myHander.handle)
        self.thread.start()

    def set_text(self,file_name):
        print("setText",threading.current_thread().name)
        self.button.setText(file_name)
class MyHandler(QObject):
    pyqtSignal =  pyqtSignal(str)
    def handle(self):
        print('handle',threading.current_thread().name)
        self.pyqtSignal.emit("Hello World")


if __name__ == '__main__':
    app = QApplication([])
    window = MyWindow()
    window.show()
    sys.exit(app.exec_())

子線(xiàn)程中調(diào)用QFileDialog

如果在子線(xiàn)程中調(diào)用了QFileDialog窗口選擇文件，QFileDialog窗口出現(xiàn)后幾秒后程序會(huì)崩潰，代碼如下

from PyQt5.QtWidgets import QApplication, QMainWindow, QPushButton,QFileDialog
from PyQt5.QtCore import QThread,pyqtSignal,QObject
import sys, threading
class MyWindow(QMainWindow):
    def __init__(self, parent=None):
        super(MyWindow, self).__init__(parent)
        self.button = QPushButton('Hi')
        self.button.clicked.connect(self.on_click)
        self.setCentralWidget(self.button)

    def on_click(self):
        print("on_click",threading.current_thread().name)
        self.thread = MyThread(self)
        self.thread.pyqtSignal.connect(self.set_text)
        self.thread.start()

    def set_text(self,file_name):
        print("setText",threading.current_thread().name)
        self.button.setText(file_name)

class MyThread(QThread):
    pyqtSignal =  pyqtSignal(str)
    def __init__(self,mv:QMainWindow) -> None:
        super().__init__(None)
        self.mv = mv

    def run(self):
        print('run',threading.current_thread().name)
        file_name = QFileDialog.getOpenFileName(self.mv, '選擇文件', './', 'Excel files(*.xlsx , *.xls)')
        print(file_name)
        self.pyqtSignal.emit("Hello World")

if __name__ == '__main__':
    app = QApplication([])
    window = MyWindow()
    window.show()
    sys.exit(app.exec_())

輸出結(jié)果：

on_click MainThread
run Dummy-1
QObject::setParent: Cannot set parent, new parent is in a different thread
CoCreateInstance failed (操作成功完成。)
QObject: Cannot create children for a parent that is in a different thread.
(Parent is QApplication(0x21fb451d190), parent's thread is QThread(0x21fb443b430), current thread is MyThread(0x21fb8788df0)
CoCreateInstance failed (操作成功完成。)
QObject::startTimer: Timers cannot be started from another thread