PyQt4中的QObject如何查询其底层C++实例是否已销毁？

Question

可以监听一个叫做 destroyed() 的信号，这个信号是针对 QObject 的。不过，我想知道有没有简单的方法来检查一个 Python 对象是否还指向一个有效的 C++ Qt 对象？有没有直接的方法可以做到这一点？

Answer 1

你可以使用Python标准库中的WeakRef类。它的用法大概是这样的：

import weakref

q = QObject()
w = weakref.ref(q)

if w() is not None: # Remember the parentheses!
    print('The QObject is still alive.')
else:
    print('Looks like the QObject died.')

Answer 2

如果你导入了sip模块，就可以使用它的.isdeleted函数。

import sip
from PyQt4.QtCore import QObject

q = QObject()
sip.isdeleted(q)
False

sip.delete(q)
q
<PyQt4.QtCore.QObject object at 0x017CCA98>

q.isdeleted(q)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: underlying C/C++ object has been deleted