Extending QML (advanced) - Attached Properties¶
This is the fifth of a series of 6 examples forming a tutorial using the example of a birthday party to demonstrate some of the advanced features of QML.
The time has come for the host to send out invitations. To keep track of which
guests have responded to the invitation and when, we need somewhere to store
that information. Storing it in the BirthdayParty
object iself would not
really fit. A better way would be to store the responses as attached objects to
the party object.
First, we declare the BirthdayPartyAttached
class which holds the guest reponses.
16
17@QmlAnonymous
18class BirthdayPartyAttached(QObject):
19 rsvp_changed = Signal()
20
21 def __init__(self, parent=None):
22 super().__init__(parent)
23 self._rsvp = QDate()
24
25 @Property(QDate, notify=rsvp_changed, final=True)
26 def rsvp(self):
27 return self._rsvp
28
29 @rsvp.setter
30 def rsvp(self, d):
31 if self._rsvp != d:
32 self._rsvp = d
And we attach it to the BirthdayParty
class and define
qmlAttachedProperties()
to return the attached object.
34
35
36@QmlElement
37@ClassInfo(DefaultProperty="guests")
38@QmlAttached(BirthdayPartyAttached)
67
68 @staticmethod
69 def qmlAttachedProperties(self, o):
Now, attached objects can be used in the QML to hold the rsvp information of the invited guests.
6BirthdayParty {
7 Boy {
8 name: "Robert Campbell"
9 BirthdayParty.rsvp: "2009-07-01"
10 }
11
12 Boy {
13 name: "Leo Hodges"
14 shoe_size: 10
15 BirthdayParty.rsvp: "2009-07-06"
16 }
17
18 host: Boy {
19 name: "Jack Smith"
20 shoe_size: 8
21 }
22}
Finally, the information can be accessed in the following way.
36 guest = party.guest(g)
37 name = guest.name
38
39 rsvp_date = None
The program outputs the following summary of the party to come:
"Jack Smith" is having a birthday!
He is inviting:
"Robert Campbell" RSVP date: "Wed Mar 1 2023"
"Leo Hodges" RSVP date: "Mon Mar 6 2023"
# 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/advanced5-Attached-properties example
from Qt v6.x"""
from pathlib import Path
import sys
from PySide6.QtCore import QCoreApplication
from PySide6.QtQml import QQmlComponent, QQmlEngine, qmlAttachedPropertiesObject
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()):
guest = party.guest(g)
name = guest.name
rsvp_date = None
attached = qmlAttachedPropertiesObject(BirthdayParty, guest, False)
if attached:
rsvp_date = attached.rsvp.toString()
if rsvp_date:
print(f" {name} RSVP date: {rsvp_date}")
else:
print(f" {name} RSVP date: Hasn't RSVP'd")
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 QDate, QObject, ClassInfo, Property, Signal
from PySide6.QtQml import QmlAnonymous, QmlAttached, 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
@QmlAnonymous
class BirthdayPartyAttached(QObject):
rsvp_changed = Signal()
def __init__(self, parent=None):
super().__init__(parent)
self._rsvp = QDate()
@Property(QDate, notify=rsvp_changed, final=True)
def rsvp(self):
return self._rsvp
@rsvp.setter
def rsvp(self, d):
if self._rsvp != d:
self._rsvp = d
self.rsvp_changed.emit()
@QmlElement
@ClassInfo(DefaultProperty="guests")
@QmlAttached(BirthdayPartyAttached)
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()
@staticmethod
def qmlAttachedProperties(self, o):
return BirthdayPartyAttached(o)
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) 2022 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
import People
BirthdayParty {
Boy {
name: "Robert Campbell"
BirthdayParty.rsvp: "2009-07-01"
}
Boy {
name: "Leo Hodges"
shoe_size: 10
BirthdayParty.rsvp: "2009-07-06"
}
host: Boy {
name: "Jack Smith"
shoe_size: 8
}
}
module People
typeinfo coercion.qmltypes
Main 1.0 Main.qml