扩展QML（高级）- 默认属性

这是使用生日派对示例来展示QML一些高级功能的6个示例系列中的第三个示例。

目前，在QML文件中，每个属性都是显式分配的。例如，host属性被分配了一个Boy，而guests属性被分配了一个Boy或Girl的列表。这很简单，但对于这个特定的用例，可以稍微简化一下。我们可以直接在聚会中添加Boy和Girl对象，并让它们隐式地分配给guests，而不是显式地分配guests属性。我们指定的所有参与者，如果不是主人，都是客人，这是有道理的。这个改变纯粹是语法上的，但在许多情况下可以增加更自然的感觉。

guests 属性可以被指定为 BirthdayParty 的默认属性。这意味着在 BirthdayParty 内创建的每个对象都会隐式地附加到默认属性 guests 上。生成的 QML 看起来像这样。

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

启用此行为所需的唯一更改是将DefaultProperty类信息注释添加到BirthdayParty，以将guests指定为其默认属性。

16
17@QmlElement
18@ClassInfo(DefaultProperty="guests")

你可能已经熟悉这个机制。在QML中，Item的所有后代的默认属性是data属性。所有未明确添加到Item的属性的元素都将被添加到data中。这使得结构清晰，并减少了代码中不必要的噪音。

下载 这个 示例

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

"""PySide6 port of the
   qml/examples/qml/tutorials/extending-qml-advanced/default advanced3-Default-properties 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) 2022 The Qt Company Ltd.
# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
from __future__ import annotations

from PySide6.QtCore import QObject, ClassInfo, 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
@ClassInfo(DefaultProperty="guests")
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 __future__ import annotations

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

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


@QmlAnonymous
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
    }

    Boy { name: "Leo Hodges" }
    Boy { name: "Jack Smith" }
    Girl { name: "Anne Brown" }
}

module People
typeinfo coercion.qmltypes
Main 1.0 Main.qml