PySide2 加载和创建组件时发生了什么？

Question

此示例有效：

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_()

该项是 QQuickItem 的 class。 component.create() 是 QQuickItem 的 class。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

怎么了？

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 的一个特殊行为，如果一个变量没有分配给一个对象，它就会被消除，所以在这种情况下，QQmlComponent 被创建但没有分配给一个变量，所以它会被删除，这与第一种情况不同，因为它是分配给变量 component，因此当想要创建项目时，组件不再存在，从而产生该错误。

一个解决方案是传递父级，因为在这种情况下可以查看延长其生命周期：

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

PySide2 加载和创建组件时发生了什么？

What's happening while PySide2 load and create component?

python

qml

python-3.x

pyside2