Python-PyQt：QThread完成后繼續

Question

我在QThread中有一個for循環，該循環是通過按鈕從主GUI啟動的。 當for循環結束時，我想回到主線程（位於Gui類內部）並執行其他操作。 據我了解，應該使用join方法來等待線程完成。 就我而言，似乎MyThread從未完成。

import sys
from PyQt5 import QtCore
import PyQt5.QtWidgets as QtW
from PyQt5.QtCore import QThread

class MyWindow(QtW.QMainWindow):

  def __init__(self):
    super().__init__()
    self.setWindowTitle('MyWindow')
    self._main = QtW.QWidget()
    self.setCentralWidget(self._main) 
    self.button = QtW.QPushButton('Do it', self)
    self.button.clicked.connect(self.MyMethod)
    self.layout = QtW.QGridLayout(self)
    self.layout.addWidget(self.button)
    self.setLayout(self.layout)


  def MyMethod(self):
    self.n = 5
    self.loadthread = MyThread(self.n)
    self.loadthread.start()
    self.loadthread.join() # Will wait for the thread until it finishes its task
    print('thread finished')


class MyThread(QThread):

    def __init__(self, n):
        QThread.__init__(self)
        self.n = n

    def run(self):
        for i in range(self.n):
            print(i)
        print('cycle finished')


if __name__ == '__main__':
    app = QtCore.QCoreApplication.instance() # checks if QApplication already exists 
    if app is None: # create QApplication if it doesnt exist 
        app = QtW.QApplication(sys.argv)
    mainGui = MyWindow()
    mainGui.show()
    app.aboutToQuit.connect(app.deleteLater)
    app.exec_()

cose的輸出是

0
1
2
3
4
cycle finished

並且永遠不會達到print('thread finished') 。

Answer 1

QThread沒有join()方法，因此您的應用程序應意外退出並指向以下錯誤消息。

QLayout: Attempting to add QLayout "" to MyWindow "", which already has a layout
QWidget::setLayout: Attempting to set QLayout "" on MyWindow "", which already has a layout
0
1
2
3
Traceback (most recent call last):
  File "main.py", line 24, in MyMethod
    self.loadthread.join() # Will wait for the thread until it finishes its task
AttributeError: 'MyThread' object has no attribute 'join'
4
cycle finished
Aborted (core dumped)

如果要在完成線程執行后執行某些任務，則必須使用QThread的finished信號：

import sys
from PyQt5 import QtCore, QtWidgets


class MyWindow(QtWidgets.QMainWindow):
    def __init__(self):
        super().__init__()
        self.setWindowTitle('MyWindow')
        self._main = QtWidgets.QWidget()
        self.setCentralWidget(self._main) 
        self.button = QtWidgets.QPushButton('Do it')
        self.button.clicked.connect(self.my_method)
        layout = QtWidgets.QGridLayout(self._main)
        layout.addWidget(self.button)
        layout.addWidget(self.button)

    @QtCore.pyqtSlot()
    def my_method(self):
        self.n = 5
        self.loadthread = MyThread(self.n, self)
        self.loadthread.finished.connect(self.on_finished)
        self.loadthread.start()

    @QtCore.pyqtSlot()
    def on_finished(self):
        print('thread finished')


class MyThread(QtCore.QThread):
    def __init__(self, n, parent=None):
        QtCore.QThread.__init__(self, parent)
        self.n = n

    def run(self):
        for i in range(self.n):
            print(i)
        print('cycle finished')


if __name__ == '__main__':
    app = QtWidgets.QApplication.instance()
    if app is None: 
        app = QtWidgets.QApplication(sys.argv)
    mainGui = MyWindow()
    mainGui.show()
    app.aboutToQuit.connect(app.deleteLater)
    sys.exit(app.exec_())