QML Component Loading

This example shows how to load a QML-defined type from Python with load_qml_component and use it by composition instead of inheritance.

person.qml defines a Person type with name and age properties, a birthdayHappened signal, and a celebrateBirthday method. The Python Employee class composes a Person instance, connects to its signal, and calls its method:

class Employee:
    """Plain Python class composing a QML Person object."""

    def __init__(self, person_factory, name, age, department):
        self.person = person_factory.create(name=name, age=age)
        self.department = department
        self.person.birthdayHappened.connect(self._on_birthday)

    def _on_birthday(self):
        print(f"{self.person.name} is now {self.person.age}!")

    def celebrate(self):
        self.person.celebrateBirthday()

Download this example

main.py

"""Load and drive a QML-defined type from Python via load_qml_component.

A ``Person`` type defined in ``person.qml`` is composed inside a plain
Python ``Employee`` class; its QML signal is connected to a Python slot
and its QML method is called from Python.
"""

import sys
from pathlib import Path

from PySide6.QtGui import QGuiApplication
from PySide6.QtQml import QQmlApplicationEngine
from PySide6.QtQmlFeatures import load_qml_component


class Employee:
    """Plain Python class composing a QML Person object."""

    def __init__(self, person_factory, name, age, department):
        self.person = person_factory.create(name=name, age=age)
        self.department = department
        self.person.birthdayHappened.connect(self._on_birthday)

    def _on_birthday(self):
        print(f"{self.person.name} is now {self.person.age}!")

    def celebrate(self):
        self.person.celebrateBirthday()


if __name__ == "__main__":
    app = QGuiApplication(sys.argv)
    engine = QQmlApplicationEngine()

    main_qml = Path(__file__).resolve().parent / "Main.qml"
    engine.load(main_qml)
    if not engine.rootObjects():
        sys.exit(-1)

    person = load_qml_component(engine, "person.qml")  # create happens in Employee constructor
    emp = Employee(person, "Alice", 28, "Engineering")
    emp.celebrate()  # prints "Alice is now 29!"

    sys.exit(app.exec())

Main.qml

import QtQuick
import QtQuick.Controls
import QtQuick.Layouts

ApplicationWindow {
    width: 400
    height: 220
    visible: true
    title: qsTr("QML Component Loading")

    ColumnLayout {
        anchors.centerIn: parent
        spacing: 16

        Label {
            text: "A QML Person is created and driven from Python."
            Layout.alignment: Qt.AlignHCenter
        }
        Label {
            text: "See the terminal for the composition output."
            Layout.alignment: Qt.AlignHCenter
        }
    }
}

person.qml

import QtQuick

QtObject {
    property string name: "John"
    property int age: 30
    signal birthdayHappened()
    function celebrateBirthday() {
        age++
        birthdayHappened()
    }
}