我在 PySide2 和 QML 工作，而 QQmlPropertyList 正在做兩件我覺得很奇怪的事情。第一個是如果 QObject 在同一語句中創建，則將其分配為值不起作用：from PySide2.QtCore import QObjectfrom PySide2.QtQml import QQmlPropertyMapqmap = QQmlPropertyMap()qmap.insert('test_key', QObject())print(qmap.value('test_key'))輸出：None也許這與 QObject 的初始化時間有關？它可以通過首先將它分配給一個變量來修復：qmap = QQmlPropertyMap()obj = QObject()qmap.insert('test_key', obj)print(qmap.value('test_key'))<PySide2.QtCore.QObject(0x7fe8f26b5eb0) at 0x107075ec0>但它變得陌生。忍受我。分配兩個 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>我什至可以將同一個對象分配給多個鍵：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>但是如果我為兩個不同的對象重用相同的變量名，第一個鍵的值會以某種方式被刪除：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>怎么會這樣？PySide 是否對運行時變量名做了某種隱藏的魔法？在這個例子中它是微不足道的，但它在我的代碼中導致了一個很難隔離的錯誤，我想更好地理解這一點。
1 回答
慕娘9325324
TA貢獻1783條經驗 獲得超4個贊
當您創建一個對象并為其分配相同的變量時，前一個對象被銷毀，可以通過以下測試觀察到：
class Foo:
def __del__(self):
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")
輸出
before creating Foo object: 1
after creating Foo object: 1
before creating Foo object: 2
destroyed
after creating Foo object: 2
destroyed
正如您所看到的，當第二個對象被分配給同一個變量時，第一個銷毀被調用。所以這不是 PySide2 的魔力而是 python 的魔力，同樣可以用被破壞的信號來驗證。
from PySide2.QtCore import QObject
print("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")
輸出：
before creating QObject object: 1
after creating QObject object: 1
before creating QObject object: 2
destroyed1: <PySide2.QtCore.QObject(0x562c1b6ee2f0) at 0x7f4a1faece40>
after creating QObject object: 2
如果你不希望這個問題發生，那么使用 Qt 的超能力，你可以將對象作為“qmap”的父對象傳遞，這樣所有權將由 QObject 持有，它將不再由 python 處理：
from PySide2.QtCore import QObject
from PySide2.QtQml import QQmlPropertyMap
qmap = 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"))
輸出：
<PySide2.QtCore.QObject(0x559629d1e230) at 0x7fef951f01c0>
<PySide2.QtCore.QObject(0x559629d1eae0) at 0x7fef951f0240>
更新：
為了更好地理解，我們必須知道PySide2（PyQt5也適用）的QObject是Qt的QObject的包裝器，也就是說，它是這樣的：
class PyQObject:
def __init__(self, *args):
self._qobject_cpp = CPPQObject(*args)
# ...
def __del__(self):
delete self._qobject_cpp
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