QQmlPropertyMap 插入；神秘地插入无，或删除其他值

Question

我在 PySide2 和 QML 工作，而 QQmlPropertyList 正在做两件我觉得很奇怪的事情。

第一个是如果 QObject 在同一语句中创建，则将其分配为值不起作用：

from PySide2.QtCore import QObject

from PySide2.QtQml import QQmlPropertyMap

qmap = QQmlPropertyMap()

qmap.insert('test_key', QObject())

print(qmap.value('test_key'))

输出：

None

也许这与 QObject 的初始化时间有关？它可以通过首先将它分配给一个变量来修复：

qmap = QQmlPropertyMap()

obj = QObject()

qmap.insert('test_key', obj)

print(qmap.value('test_key'))

<PySide2.QtCore.QObject(0x7fe8f26b5eb0) at 0x107075ec0>

但它变得陌生。忍受我。分配两个 QObjects 工作：

qmap = QQmlPropertyMap()

obj = QObject()

qmap.insert('test_key', obj)

obj2 = QObject()

qmap.insert('test_key2', obj2)

print(qmap.value('test_key'))

print(qmap.value('test_key2'))

<PySide2.QtCore.QObject(0x7f85f7f269e0) at 0x10d32b080>

<PySide2.QtCore.QObject(0x7f85f7f26b70) at 0x10d32b100>

我什至可以将同一个对象分配给多个键：

qmap = QQmlPropertyMap()

obj = QObject()

qmap.insert('test_key', obj)

qmap.insert('test_key2', obj)

print(qmap.value('test_key'))

print(qmap.value('test_key2'))

<PySide2.QtCore.QObject(0x7fde37d7d9d0) at 0x105cdc140>

<PySide2.QtCore.QObject(0x7fde37d7d9d0) at 0x105cdc140>

但是如果我为两个不同的对象重用相同的变量名，第一个键的值会以某种方式被删除：

qmap = QQmlPropertyMap()

obj = QObject()

qmap.insert('test_key', obj)

obj = QObject()

qmap.insert('test_key2', obj)

print(qmap.value('test_key'))

print(qmap.value('test_key2'))

None

<PySide2.QtCore.QObject(0x7fcecaf072f0) at 0x111ba60c0>

怎么会这样？PySide 是否对运行时变量名做了某种隐藏的魔法？在这个例子中它是微不足道的，但它在我的代码中导致了一个很难隔离的错误，我想更好地理解这一点。

Answer 1

当您创建一个对象并为其分配相同的变量时，前一个对象被销毁，可以通过以下测试观察到：class Foo:&nbsp; &nbsp; def __del__(self):&nbsp; &nbsp; &nbsp; &nbsp; print("destroyed")print("before creating Foo object: 1")foo = Foo()print("after creating Foo object: 1")print("before creating Foo object: 2")foo = Foo()print("after creating Foo object: 2")输出before creating Foo object: 1after creating Foo object: 1before creating Foo object: 2destroyedafter creating Foo object: 2destroyed正如您所看到的，当第二个对象被分配给同一个变量时，第一个销毁被调用。所以这不是 PySide2 的魔力而是 python 的魔力，同样可以用被破坏的信号来验证。from PySide2.QtCore import QObjectprint("before creating QObject object: 1")qobject = QObject()qobject.destroyed.connect(lambda _id=id(qobject): print("destroyed1: ", _id))print("after creating QObject object: 1")print("before creating QObject object: 2")qobject = QObject()qobject.destroyed.connect(lambda _id=id(qobject): print("destroyed2: ", _id))print("after creating QObject object: 2")输出：before creating QObject object: 1after creating QObject object: 1before creating QObject object: 2destroyed1:&nbsp; <PySide2.QtCore.QObject(0x562c1b6ee2f0) at 0x7f4a1faece40>after creating QObject object: 2如果你不希望这个问题发生，那么使用 Qt 的超能力，你可以将对象作为“qmap”的父对象传递，这样所有权将由 QObject 持有，它将不再由 python 处理：from PySide2.QtCore import QObjectfrom PySide2.QtQml import QQmlPropertyMapqmap = QQmlPropertyMap()obj = QObject(qmap)qmap.insert("test_key", obj)obj = QObject(qmap)qmap.insert("test_key2", obj)print(qmap.value("test_key"))print(qmap.value("test_key2"))输出：<PySide2.QtCore.QObject(0x559629d1e230) at 0x7fef951f01c0><PySide2.QtCore.QObject(0x559629d1eae0) at 0x7fef951f0240>更新：为了更好地理解，我们必须知道PySide2（PyQt5也适用）的QObject是Qt的QObject的包装器，也就是说，它是这样的：class PyQObject:&nbsp; &nbsp; def __init__(self, *args):&nbsp; &nbsp; &nbsp; &nbsp; self._qobject_cpp = CPPQObject(*args)&nbsp; &nbsp; &nbsp; &nbsp; # ...&nbsp; &nbsp; def __del__(self):&nbsp; &nbsp; &nbsp; &nbsp; delete self._qobject_cpp