python - PySide2 加载和创建组件时发生了什么？

Question

这个例子正在运行:

from PySide2.QtCore import QUrl
from PySide2.QtGui import QGuiApplication
from PySide2.QtQml import QQmlComponent
from PySide2.QtQuick import QQuickView

app = QGuiApplication()
view = QQuickView()
engine = view.engine()
url = QUrl("main.qml")
view.setSource(url)
component = QQmlComponent(engine, QUrl.fromLocalFile("block.qml"))
item = component.create()
item.setParent(view.rootObject())
item.setParentItem(view.rootObject())
view.show()
app.exec_()

该项目是 QQuickItem 的类。component.create()是QQuickItem的一个类。将此示例更改为:

from PySide2.QtCore import QUrl
from PySide2.QtGui import QGuiApplication
from PySide2.QtQml import QQmlComponent
from PySide2.QtQuick import QQuickView

app = QGuiApplication()
view = QQuickView()
engine = view.engine()
url = QUrl("main.qml")
view.setSource(url)
item = QQmlComponent(engine, QUrl.fromLocalFile("block.qml")).create()
item.setParent(view.rootObject())
item.setParentItem(view.rootObject())
view.show()
app.exec_()

抛出异常:

Traceback (most recent call last):
File "/home/babywolf/dev/apps/qttest/test.py", line 14, in <module>     
item.setParent(view.rootObject())
RuntimeError: Internal C++ object (PySide2.QtQuick.QQuickItem) already deleted.
Process finished with exit code 1

出了什么问题？

main.qml:

import QtQuick 2.0

Rectangle {
    width: 200
    height: 200
    color: "green"
}

block .qml:

import QtQuick 2.0

Text {
    text: "Hello World"
    anchors.centerIn: parent
}

Answer 1

这是 PySide 的一种特殊行为，如果变量未分配给对象，它将被消除，因此在这种情况下，QQmlComponent 被创建但未分配给变量，因此与第一种情况不同，它将被删除，因为它被分配给变量组件，因此当想要创建该项目时，该组件不再存在并生成该错误。

一种解决方案是传递父级，因为在本例中可以查看延长其生命周期:

item = QQmlComponent(engine, QUrl.fromLocalFile("block.qml"), view).create()
#                                                               └----- parent