请考虑下面这个最小的例子,它实现了一个自定义的 QNetworkAccessManager
列表,维护一个未完成的 QNetworkReply
实例。
当答复是 finished
,它被从 unfinished_replies
列表。
中所讨论的。在PyQtPySide中需要deleteLater()吗?, QNetworkReply.deleteLater()
使用的,里面的 finished
槽,来安排Qt对象的删除。
然而,我不确定删除回复对象的Python引用的最佳方式是什么。我可以想到两种 (相互排斥的) 删除 Python 引用的方法,如下例所示。
直接在调用 deleteLater()
撤下 QNetworkReply.destroyed
发出信号(文件)
两种方案似乎都很好用。我更倾向于选择1,但我不知道这是否会导致在极少数情况下出现意外。哪种方案最好?还是有其他的选择?
import sys
from PyQt5 import QtNetwork, QtWidgets, QtCore
class CustomNetworkAccessManager(QtNetwork.QNetworkAccessManager):
def __init__(self):
super(CustomNetworkAccessManager, self).__init__()
self.unfinished_replies = []
self.finished.connect(self.slot)
def get(self, *args, **kwargs):
reply = super(CustomNetworkAccessManager, self).get(*args, **kwargs)
reply.index = i # just for printing
self.unfinished_replies.append(reply)
def remove_from_list(self, reply):
self.unfinished_replies.remove(reply)
print('{} unfinished replies left'.format(len(self.unfinished_replies)))
if not self.unfinished_replies:
QtCore.QCoreApplication.quit()
def slot(self, reply):
print('reply {} finished'.format(reply.index))
# handle the Qt side:
reply.deleteLater()
# handle the Python side:
# either
# OPTION 1 - remove now
self.remove_from_list(reply)
# or
# OPTION 2 - remove when destroyed
# reply.destroyed.connect(lambda: self.remove_from_list(reply))
if __name__ == '__main__':
# Initialize
app = QtWidgets.QApplication(sys.argv)
manager = CustomNetworkAccessManager()
# Schedule requests
url = 'http://httpbin.org/get'
for i in range(6):
manager.get(QtNetwork.QNetworkRequest(QtCore.QUrl(url)))
# Start event loop
app.exec_()
p.s.对不起,Python 2的代码。
两者都是等价的,只是在删除的那一刻不同。但是要想更详细的理解,你必须了解PyQt5PySide2绑定的工作原理。这些库围绕C++对象创建了一个封装器,类似于。
class FooWrapper:
def __new__(self, cls, *args, **kwargs):
# ...
instance = ...
instance._cpp_object = create_cpp_object()
# ...
return instance
def foo_method(self, *args, **kwargs):
return execute_foo_method(self._cpp_object, *args, **kwargs)
def __del__(self):
destroyed_cpp_object(self._cpp_object)
所以当调用deleteLater时,只有cpp_object被删除,而不是包装器, 你可以通过使用:
reply.destroyed.connect(self.remove_from_list)
Traceback (most recent call last):
File "main.py", line 32, in <lambda>
reply.destroyed.connect(self.remove_from_list)
File "main.py", line 17, in remove_from_list
self.unfinished_replies.remove(reply)
ValueError: list.remove(x): x not in list
因为destroy传递的参数是一个无效的包装器,会出现上述错误。对于这种情况,一个解决方案是用sip.isdeleted()检查cpp_object是否已经被删除。
from PyQt5 import QtNetwork, QtWidgets, QtCore
import sip
# ...
class CustomNetworkAccessManager(QtNetwork.QNetworkAccessManager):
# ...
def remove_from_list(self):
self.unfinished_replies = [
reply for reply in self.unfinished_replies if not sip.isdeleted(reply)
]
print("{} unfinished replies left".format(len(self.unfinished_replies)))
if not self.unfinished_replies:
QtCore.QCoreApplication.quit()
def slot(self, reply):
print("reply {} finished".format(reply.index))
# handle the Qt side:
reply.deleteLater()
# handle the Python side:
reply.destroyed.connect(self.remove_from_list)
回到对你的方法的研究, 这些方法可以绘制成如下图:
(FIRST METHOD)
------------┬------------------┬---------------------┬-----------------------
| | |
call_deleteLater remove_reply_from_list destroyed
(SECOND METHOD)
------------┬-----------------------------------------┬-----------------┬------
| | |
call_deleteLater destroyed remove_reply_from_list
由于你使用的是原始的封装器,你应该不会有任何问题。
结论。 两者都是等价和安全的。