如何使 PySide.QtCore.QTimer.singleShot 调用其超时方法

Question

I am working on a complex and poorly commented Qt-based Python application. It employs a PySide.QtCore.QTimer.singleShot(int,slot) timer to delay the execution of a slot within a thread, and I am confused about how this timer works.

Here is a MWE. This example uses the approach of subclassing QThread and reimplementing 运行(). I put the following in a file called timertester.py:

import PySide
import time

class SubClassThread(PySide.QtCore.QThread):

        def run(self):
                print('called SubClassThread.run()')
                self.delayed_print()

        def delayed_print(self):
                print('called SubClassThread.delayed_print()')
                PySide.QtCore.QTimer.singleShot(1000, self.print_things)
                time.sleep(2)
                print('end of delayed_print()')

        def print_things(self):
                print('called print_things')

The code I am using to test this (call it test.py):

import sys
import time

import PySide

from timertester import SubClassThread

print('Test: QThread subclassing')
app = PySide.QtCore.QCoreApplication([])
sct = SubClassThread()
sct.finished.connect(app.exit)
sct.start()
sys.exit(app.exec_())

The output of python test.py:

Test: QThread subclassing
called SubClassThread.run()
called SubClassThread.delayed_print()
end of delayed_print()

The curious part is that the callable passed to QTimer.singleShot never seems to get called (there is no called print_things() in the output!) I would greatly appreciate any clarity that you can shed on this. I feel that I am missing some simple ingredient of the Qt framework. Please bear with me- I did spend some hours searching for answers to this.

Answer 1

QThread.run() 的默认实现调用 QThread.exec()，它启动线程自己的事件循环。 QTimer 需要一个运行事件循环，它的 timeout() 信号将在它启动的线程中发出。您的 run() 实现不会启动事件-循环，所以定时器什么都不做。

Answer 2

正如@ekhumoro 所指出的，我对运行() 的重新实现未能调用 exec_()。这是主要问题。我花了一分钟才弄清楚将 exec_() 调用放在哪里，以及如何在线程工作完成后正确地 quit() 线程。这是有效的代码。

Class 定义，timertester.py:

import PySide

class SubClassThread(PySide.QtCore.QThread):

        def __init__(self,parent=None):
                print('called SubClassThread.__init__()')
                super(SubClassThread,self).__init__(parent)

        def run(self):
                print('called SubClassThread.run()')
                self.delayed_print()
                self.exec_()

        def delayed_print(self):
                print('called SubClassThread.delayed_print()')
                PySide.QtCore.QTimer.singleShot(1000, self.print_things)
                print('end of delayed_print()')

        def print_things(self):
                print('called print_things')
                self.quit()

申请，test.py：

import sys

import PySide

from timertester import SubClassThread

print('Test: QThread subclassing')

# instantiate a QApplication
app = PySide.QtCore.QCoreApplication([])

# instantiate a thread
sct = SubClassThread()

# when the thread finishes, make sure the app quits too
sct.finished.connect(app.quit)

# start the thread
# it will do nothing until the app's event loop starts
sct.start()

# app.exec_() starts the app's event loop. 
# app will then wait for signals from QObjects.
status=app.exec_()

# print status code and exit gracefully
print('app finished with exit code {}'.format(status))
sys.exit(status)

最后，python test.py 的输出：

Test: QThread subclassing
called SubClassThread.__init__()
called SubClassThread.run()
called SubClassThread.delayed_print()
end of delayed_print()
called print_things
app finished with exit code 0

我对 QTimers 的了解：对 delayed_print() 的调用在计时器仍在运行ning 时完成，并且通过将 quit() 放入计时器调用的方法中，应用程序在调用该方法之前不会退出。

如果对此代码或与此简单应用程序相关的 Qt 方面有任何进一步的评论，请post！我在为初学者寻找可访问的 PyQt/PySide 信息时遇到了一些麻烦。

如何使 PySide.QtCore.QTimer.singleShot 调用其超时方法

How to make a PySide.QtCore.QTimer.singleShot call its timeout method

python

multithreading

qt

pyside

qtimer