Extending QML (advanced) - Property Value Source¶
This is the last 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.
During the party the guests have to sing for the host. It would be handy if the program could display the lyrics customized for the occasion to help the guests. To this end, a property value source is used to generate the verses of the song over time.
13
14@QmlElement
15class HappyBirthdaySong(QPyQmlPropertyValueSource):
16 name_changed = Signal()
17
18 def __init__(self, parent=None):
19 super().__init__(parent)
20
21 self.m_target = None
22 self.m_name = ""
23 self.m_line = -1
24 self.m_lyrics = []
25
26 self.m_timer = QTimer(self)
27 self.m_timer.timeout.connect(self.advance)
28 self.m_timer.start(1000)
29
30 def setTarget(self, property):
31 self.m_target = property
32
33 @Property(str, notify=name_changed, final=True)
34 def name(self):
35 return self.m_name
36
37 @name.setter
38 def name(self, n):
39 if self.m_name != n:
40 self.m_name = n
41 self.m_lyrics = ["Happy birthday to you,",
42 "Happy birthday to you,",
43 f"Happy birthday dear {self.m_name},",
44 "Happy birthday to you!",
45 ""]
46
47 @Slot()
48 def advance(self):
49 self.m_line = (self.m_line + 1) % len(self.m_lyrics)
The class HappyBirthdaySong
is added as a value source. It must inherit
from QQmlPropertyValueSource
and implement its interface. The
setTarget()
function is used to define which property this source acts
upon. In this case, the value source writes to the announcement
property of
the BirthdayParty
to display the lyrics over time. It has an internal timer
that causes the announcement
property of the party to be set to the next
line of the lyrics repeatedly.
In QML, a HappyBirthdaySong
is instantiated inside the BirthdayParty
.
The on
keyword in its signature is used to specify the property that the
value source targets, in this case announcement
. The name
property of
the HappyBirthdaySong
object is also bound to the name of the host of the
party.
6BirthdayParty {
7 HappyBirthdaySong on announcement { name: "Bob Jones" }
The program displays the time at which the party started using the
partyStarted
signal and then prints the following happy birthday verses
over and over:
Happy birthday to you,
Happy birthday to you,
Happy birthday dear Bob Jones,
Happy birthday to you!
# 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/advanced6-Property-value-source 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
from happybirthdaysong import HappyBirthdaySong # 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")
party.startParty()
r = app.exec()
del engine
sys.exit(r)
# 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, QTime, 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):
announcement_changed = Signal()
host_changed = Signal()
guests_changed = Signal()
partyStarted = Signal(QTime)
def __init__(self, parent=None):
super().__init__(parent)
self._announcement = ""
self._host = None
self._guests = []
def startParty(self):
self.partyStarted.emit(QTime.currentTime())
@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()
@Property(str, notify=announcement_changed, final=True)
def announcement(self):
return self._announcement
@announcement.setter
def announcement(self, a):
if self._announcement != a:
self._announcement = a
self.announcement_changed.emit()
print(a)
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 QTimer, Property, Signal, Slot
from PySide6.QtQml import QmlElement, QPyQmlPropertyValueSource
# To be used on the @QmlElement decorator
# (QML_IMPORT_MINOR_VERSION is optional)
QML_IMPORT_NAME = "People"
QML_IMPORT_MAJOR_VERSION = 1
@QmlElement
class HappyBirthdaySong(QPyQmlPropertyValueSource):
name_changed = Signal()
def __init__(self, parent=None):
super().__init__(parent)
self.m_target = None
self.m_name = ""
self.m_line = -1
self.m_lyrics = []
self.m_timer = QTimer(self)
self.m_timer.timeout.connect(self.advance)
self.m_timer.start(1000)
def setTarget(self, property):
self.m_target = property
@Property(str, notify=name_changed, final=True)
def name(self):
return self.m_name
@name.setter
def name(self, n):
if self.m_name != n:
self.m_name = n
self.m_lyrics = ["Happy birthday to you,",
"Happy birthday to you,",
f"Happy birthday dear {self.m_name},",
"Happy birthday to you!",
""]
@Slot()
def advance(self):
self.m_line = (self.m_line + 1) % len(self.m_lyrics)
self.m_target.write(self.m_lyrics[self.m_line])
# 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 {
HappyBirthdaySong on announcement { name: "Bob Jones" }
onPartyStarted: (time) => { console.log("This party started rockin' at " + time); }
host: Boy {
name: "Bob Jones"
shoe_size: 12
}
Boy {
name: "Leo Hodges"
BirthdayParty.rsvp: "2009-07-06"
}
Boy {
name: "Jack Smith"
}
Girl {
name: "Anne Brown"
BirthdayParty.rsvp: "2009-07-01"
}
}
module People
typeinfo coercion.qmltypes
Main 1.0 Main.qml