Extending QML - Value Source Example#

This example builds on the Extending QML - Adding Types Example, the Extending QML - Attached Properties Example, the Extending QML - Default Property Example, the Extending QML - Inheritance and Coercion Example and the Extending QML - Object and List Property Types Example.

It demonstrates implementing a property value source in Python.

Running the Example#

The main.py file in the example includes a simple shell application that loads and runs the QML snippet shown below.

"""PySide6 port of the qml/examples/qml/referenceexamples/valuesource example from Qt v6.x"""

from pathlib import Path
import sys

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

from person import Boy, Girl
from birthdayparty import BirthdayParty
from happybirthdaysong import HappyBirthdaySong


app = QCoreApplication(sys.argv)
qml_file = Path(__file__).parent / "example.qml"
url = QUrl.fromLocalFile(qml_file)
engine = QQmlEngine()
component = QQmlComponent(engine, url)
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)
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 = "examples.valuesource.people"
QML_IMPORT_MAJOR_VERSION = 1


@QmlAnonymous
class BirthdayPartyAttached(QObject):

    def __init__(self, parent=None):
        super().__init__(parent)
        self._rsvp = QDate()

    @Property(QDate)
    def rsvp(self):
        return self._rsvp

    @rsvp.setter
    def rsvp(self, d):
        self._rsvp = d


@QmlElement
@ClassInfo(DefaultProperty="guests")
@QmlAttached(BirthdayPartyAttached)
class BirthdayParty(QObject):

    partyStarted = Signal(QTime)

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

    def startParty(self):
        self.partyStarted.emit(QTime.currentTime())

    @Property(Person)
    def host(self):
        return self._host

    @host.setter
    def host(self, h):
        self._host = h

    @Property(str)
    def announcement(self):
        return ""

    @announcement.setter
    def announcement(self, a):
        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)

    @staticmethod
    def qmlAttachedProperties(self, o):
        return BirthdayPartyAttached(o)

    guests = ListProperty(Person, appendGuest)
from PySide6.QtCore import QObject, QTimer, Property, Slot
from PySide6.QtQml import QmlElement, QPyQmlPropertyValueSource

# To be used on the @QmlElement decorator
# (QML_IMPORT_MINOR_VERSION is optional)
QML_IMPORT_NAME = "examples.valuesource.people"
QML_IMPORT_MAJOR_VERSION = 1


@QmlElement
class HappyBirthdaySong(QPyQmlPropertyValueSource):

    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)
    def name(self):
        return self.m_name

    @name.setter
    def name(self, 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])
from PySide6.QtCore import QObject, Property
from PySide6.QtQml import QmlAnonymous, QmlElement

# To be used on the @QmlElement decorator
# (QML_IMPORT_MINOR_VERSION is optional)
QML_IMPORT_NAME = "examples.valuesource.people"
QML_IMPORT_MAJOR_VERSION = 1


@QmlAnonymous
class Person(QObject):
    def __init__(self, parent=None):
        super().__init__(parent)
        self._name = ''
        self._shoe_size = 0

    @Property(str)
    def name(self):
        return self._name

    @name.setter
    def name(self, n):
        self._name = n

    @Property(int)
    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)
import examples.valuesource.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"
    }
}