在 PyQt6 中使用多个对话框取消长时间运行的操作

Question

我在 PyQt6 中遇到线程问题。我在How to stop a QThread from the GUI and rebuild it with a separate dialog and a finished event.

的解决方案中使用了很好的例子。

理论上，我要创建的是一个连接对话框，它打开与 oracledb 的数据库连接。虽然，如果我在连接对话框中单击连接，它不应该静默连接，但它应该显示一个取消对话框，如果我愿意，我可以选择取消当前的连接尝试。 这个功能稍后应该用于我程序中对数据库的每个查询，连接对话框只是一个例子。

我当前的问题是取消对话框上的按钮未显示。即使我使用线程让工作人员连接，取消对话框也会以某种方式被冻结。

为此，我创建了以下简化代码示例：

import time

from PyQt6.QtCore import *
from PyQt6.QtGui import *
from PyQt6.QtWidgets import *


class ConnectionDialog(QDialog):
    def __init__(self):
        super().__init__()
        self.database = -1
        self.setFixedSize(QSize(200, 100))

        # create CancelDialog but do not display yet
        self.cancel_dialog = CancelDialog(self)

        # creat a thread
        self.thread = QThread()
        self.thread.start()

        # creat a worker and put it on thread
        self.worker = Worker()
        self.worker.moveToThread(self.thread)

        # create button which triggers the cancel_dialog and therefore the connection attempt
        self.btnStart = QPushButton("Connect")
        self.btnStart.clicked.connect(self.start_worker)

        # if the worker emits finished call helper function end_thread
        self.worker.finished.connect(self.end_thread)

        # create dummy layout to display the button
        self.layout = QHBoxLayout()
        self.layout.addWidget(self.btnStart)
        self.setLayout(self.layout)

    # helper function to quit and wait for the thread
    def end_thread(self, connection):
        self.worker.stop()
        self.thread.quit()
        self.thread.wait()
        print(f"Connected to {connection}")
        self.close()
        # push connection to self.database for further use
        self.database = connection

    # helper function to start worker in thread
    def start_worker(self):
        self.cancel_dialog.show()
        self.worker.task()


class CancelDialog(QDialog):
    def __init__(self, parent):
        super().__init__(parent)
        self.setModal(True)
        # create button for the cancel operation for the thread of the parent
        self.btnStop = QPushButton("Cancel")
        self.btnStop.clicked.connect(lambda: self.cancel_thread())

        # create dummy layout to display the button
        self.layout = QHBoxLayout()
        self.layout.addWidget(self.btnStop)
        self.setLayout(self.layout)

    # helper function when pressing cancel button
    def cancel_thread(self):
        # stop worker
        self.parent().worker.stop()
        # quit thread, this time we dont want to wait for the thread
        self.parent().thread.quit()
        print("Canceled")
        self.close()
        # push error value to self.database
        self.parent().database = -1


class Worker(QObject):
    "Object managing the simulation"
    finished = pyqtSignal(int)

    def __init__(self):
        super().__init__()
        self._isRunning = True
        self.connection = -1

    def task(self):
        if not self._isRunning:
            self._isRunning = True
        # this simulates a database connection
        print("connecting...")
        print("fake delay before connection")
        time.sleep(3)
        print("really connecting now")
        self.connection = 123
        print("fake delay after connection")
        time.sleep(3)
        print("really connecting now")
        self.finished.emit(self.connection)
        print("finished connecting")

    def stop(self):
        self._isRunning = False
        if self.connection:
            self.connection = 0
            print("Canceled")


if __name__ == "__main__":
    app = QApplication(sys.argv)
    simul = ConnectionDialog()
    simul.show()
    sys.exit(app.exec())