扩展QML（高级）- 继承和转换#

这是6例教程系列中的第二个示例，使用生日派对作为示例来展示一些QML的高级功能。

目前，每位参与者都被模拟为一个人。这有点太通用，而且最好能够更多地了解参与者。通过将他们区分为男孩和女孩，我们可以更好地了解谁会来。

要做到这一点，引入了Boy和Girl类，它们都继承自Person。

43@QmlElement
44class Boy(Person):
45    def __init__(self, parent=None):
46        super().__init__(parent)

49@QmlElement
50class Girl(Person):
51    def __init__(self, parent=None):
52        super().__init__(parent)

Person类保持不变，Boy和Girl类是它的简单扩展。类型及其QML名称通过@QmlElement注册到QML引擎中。

注意，在BirthdayParty中，host和guests属性仍然接受Person的实例。

26    @Property(Person, notify=host_changed, final=True)

46    guests = ListProperty(Person, appendGuest, notify=guests_changed, final=True)

《Person》类的实现并未改变。然而，由于《Person》类被重新用于作为《Boy》和《Girl》的通用基类，因此《Person》不应再直接从 QML 中实例化。应显式实例化《Boy》或《Girl》。

13@QmlElement
14@QmlUncreatable("Person is an abstract base class.")
15class Person(QObject):

虽然我们希望阻止在 QML 中实例化《Person》，但《Person》仍然需要登记到 QML 引擎，以便可以使用它作为属性类型以及其他类型可以被强制转换为它。这正是《@QmlUncreatable》宏所做的事情。由于三种类型，《Person》、《Boy》和《Girl》，都已在 QML 系统中登记，在赋值时，QML 会自动（并且类型安全地）将《Boy》和《Girl》对象转换为《Person》。

实现了这些更改后，我们现在可以指定生日派对，并提供有关参加者的额外信息，如下所示。

 6BirthdayParty {
 7    host: Boy {
 8        name: "Bob Jones"
 9        shoe_size: 12
10    }
11    guests: [
12        Boy { name: "Leo Hodges" },
13        Boy { name: "Jack Smith" },
14        Girl { name: "Anne Brown" }
15    ]
16}

下载此示例

# Copyright (C) 2022 The Qt Company Ltd.
# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

"""PySide6 port of the
   qml/examples/qml/tutorials/extending-qml-advanced/advanced2-Inheritance-and-coercion example
   from Qt v6.x"""

from pathlib import Path
import sys

from PySide6.QtCore import QCoreApplication
from PySide6.QtQml import QQmlComponent, QQmlEngine

from person import Boy, Girl  # noqa: F401
from birthdayparty import BirthdayParty  # noqa: F401


app = QCoreApplication(sys.argv)
engine = QQmlEngine()
engine.addImportPath(Path(__file__).parent)
component = QQmlComponent(engine)
component.loadFromModule("People", "Main")
party = component.create()
if not party:
    print(component.errors())
    del engine
    sys.exit(-1)
host = party.host
print(f"{host.name} is having a birthday!")
if isinstance(host, Boy):
    print("He is inviting:")
else:
    print("She is inviting:")
for g in range(party.guestCount()):
    name = party.guest(g).name
    print(f"    {name}")
del engine
sys.exit(0)

# Copyright (C) 2023 The Qt Company Ltd.
# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

from PySide6.QtCore import QObject, Property, Signal
from PySide6.QtQml import QmlElement, ListProperty

from person import Person


# To be used on the @QmlElement decorator
# (QML_IMPORT_MINOR_VERSION is optional)
QML_IMPORT_NAME = "People"
QML_IMPORT_MAJOR_VERSION = 1


@QmlElement
class BirthdayParty(QObject):
    host_changed = Signal()
    guests_changed = Signal()

    def __init__(self, parent=None):
        super().__init__(parent)
        self._host = None
        self._guests = []

    @Property(Person, notify=host_changed, final=True)
    def host(self):
        return self._host

    @host.setter
    def host(self, h):
        if self._host != h:
            self._host = h
            self.host_changed.emit()

    def guest(self, n):
        return self._guests[n]

    def guestCount(self):
        return len(self._guests)

    def appendGuest(self, guest):
        self._guests.append(guest)
        self.guests_changed.emit()

    guests = ListProperty(Person, appendGuest, notify=guests_changed, final=True)

# Copyright (C) 2022 The Qt Company Ltd.
# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

from PySide6.QtCore import QObject, Property, Signal
from PySide6.QtQml import QmlElement, QmlUncreatable

# To be used on the @QmlElement decorator
# (QML_IMPORT_MINOR_VERSION is optional)
QML_IMPORT_NAME = "People"
QML_IMPORT_MAJOR_VERSION = 1


@QmlElement
@QmlUncreatable("Person is an abstract base class.")
class Person(QObject):
    name_changed = Signal()
    shoe_size_changed = Signal()

    def __init__(self, parent=None):
        super().__init__(parent)
        self._name = ''
        self._shoe_size = 0

    @Property(str, notify=name_changed, final=True)
    def name(self):
        return self._name

    @name.setter
    def name(self, n):
        if self._name != n:
            self._name = n
            self.name_changed.emit()

    @Property(int, notify=shoe_size_changed, final=True)
    def shoe_size(self):
        return self._shoe_size

    @shoe_size.setter
    def shoe_size(self, s):
        self._shoe_size = s


@QmlElement
class Boy(Person):
    def __init__(self, parent=None):
        super().__init__(parent)


@QmlElement
class Girl(Person):
    def __init__(self, parent=None):
        super().__init__(parent)

// Copyright (C) 2021 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

import People

BirthdayParty {
    host: Boy {
        name: "Bob Jones"
        shoe_size: 12
    }
    guests: [
        Boy { name: "Leo Hodges" },
        Boy { name: "Jack Smith" },
        Girl { name: "Anne Brown" }
    ]
}

module People
typeinfo coercion.qmltypes
Main 1.0 Main.qml