QML Application Tutorial

This tutorial provides a quick walk-through of a python application that loads a QML file. QML is a declarative language that lets you design UIs faster than a traditional language, such as C++. The QtQml and QtQuick modules provides the necessary infrastructure for QML-based UIs.

In this tutorial, you’ll also learn how to provide data from Python as a QML context property, which is then consumed by the ListView defined in the QML file.

Before you begin, install the following prerequisites:

The following step-by-step instructions guide you through application development process using Qt Creator:

  1. Open Qt Creator and select File > New File or Project.. menu item to open following dialog:

    ../../_images/newpyproject.png

  2. Select Qt for Python - Empty from the list of application templates and select Choose.

    ../../_images/pyprojname.png

  3. Give a Name to your project, choose its location in the filesystem, and select Finish to create an empty main.py and main.pyproject.

    ../../_images/pyprojxplor.png

    This should create a main.py and `main.pyproject files for the project.

  4. Download view.qml and logo.png and move them to your project folder.

  5. Double-click on main.pyproject to open it in edit mode, and append view.qml and logo.png to the files list. This is how your project file should look after this change:

    {
    "files": ["main.py", "view.qml", "logo.png"]
}

  6. Now that you have the necessary bits for the application, import the Python modules in your main.py, and download country data and format it:

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#!/usr/bin/env python
# -*- conding: utf-8 -*-

import os, sys, urllib.request, json
import PySide2.QtQml
from PySide2.QtQuick import QQuickView
from PySide2.QtCore import QStringListModel, Qt, QUrl
from PySide2.QtGui import QGuiApplication

if __name__ == '__main__':

    #get our data
    url = "http://country.io/names.json"
    response = urllib.request.urlopen(url)
    data = json.loads(response.read().decode('utf-8'))

    #Format and sort the data
    data_list = list(data.values())
    data_list.sort()

  7. Now, set up the application window using PySide2.QtGui.QGuiApplication, which manages the application-wide settings.

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#!/usr/bin/env python
# -*- conding: utf-8 -*-

import os, sys, urllib.request, json
import PySide2.QtQml
from PySide2.QtQuick import QQuickView
from PySide2.QtCore import QStringListModel, Qt, QUrl
from PySide2.QtGui import QGuiApplication

if __name__ == '__main__':

    #get our data
    url = "http://country.io/names.json"
    response = urllib.request.urlopen(url)
    data = json.loads(response.read().decode('utf-8'))

    #Format and sort the data
    data_list = list(data.values())
    data_list.sort()

    #Set up the application window
    app = QGuiApplication(sys.argv)
    view = QQuickView()
    view.setResizeMode(QQuickView.SizeRootObjectToView)

    Note

    Setting the resize policy is important if you want the root item to resize itself to fit the window or vice-a-versa. Otherwise, the root item will retain its original size on resizing the window.

  8. You can now expose the data_list variable as a QML context property, which will be consumed by the QML ListView item in view.qml.

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#!/usr/bin/env python
# -*- conding: utf-8 -*-

import os, sys, urllib.request, json
import PySide2.QtQml
from PySide2.QtQuick import QQuickView
from PySide2.QtCore import QStringListModel, Qt, QUrl
from PySide2.QtGui import QGuiApplication

if __name__ == '__main__':

    #get our data
    url = "http://country.io/names.json"
    response = urllib.request.urlopen(url)
    data = json.loads(response.read().decode('utf-8'))

    #Format and sort the data
    data_list = list(data.values())
    data_list.sort()

    #Set up the application window
    app = QGuiApplication(sys.argv)
    view = QQuickView()
    view.setResizeMode(QQuickView.SizeRootObjectToView)

    #Expose the list to the Qml code
    my_model = QStringListModel()
    my_model.setStringList(data_list)
    view.rootContext().setContextProperty("myModel",my_model)

  9. Load the view.qml to the QQuickView and call show() to display the application window.

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#!/usr/bin/env python
# -*- conding: utf-8 -*-

import os, sys, urllib.request, json
import PySide2.QtQml
from PySide2.QtQuick import QQuickView
from PySide2.QtCore import QStringListModel, Qt, QUrl
from PySide2.QtGui import QGuiApplication

if __name__ == '__main__':

    #get our data
    url = "http://country.io/names.json"
    response = urllib.request.urlopen(url)
    data = json.loads(response.read().decode('utf-8'))

    #Format and sort the data
    data_list = list(data.values())
    data_list.sort()

    #Set up the application window
    app = QGuiApplication(sys.argv)
    view = QQuickView()
    view.setResizeMode(QQuickView.SizeRootObjectToView)

    #Expose the list to the Qml code
    my_model = QStringListModel()
    my_model.setStringList(data_list)
    view.rootContext().setContextProperty("myModel",my_model)

    #Load the QML file
    qml_file = os.path.join(os.path.dirname(__file__),"view.qml")
    view.setSource(QUrl.fromLocalFile(os.path.abspath(qml_file)))

    #Show the window
    if view.status() == QQuickView.Error:
        sys.exit(-1)
    view.show()

  10. Finally, execute the application to start the event loop and clean up.

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#!/usr/bin/env python
# -*- conding: utf-8 -*-

import os, sys, urllib.request, json
import PySide2.QtQml
from PySide2.QtQuick import QQuickView
from PySide2.QtCore import QStringListModel, Qt, QUrl
from PySide2.QtGui import QGuiApplication

if __name__ == '__main__':

    #get our data
    url = "http://country.io/names.json"
    response = urllib.request.urlopen(url)
    data = json.loads(response.read().decode('utf-8'))

    #Format and sort the data
    data_list = list(data.values())
    data_list.sort()

    #Set up the application window
    app = QGuiApplication(sys.argv)
    view = QQuickView()
    view.setResizeMode(QQuickView.SizeRootObjectToView)

    #Expose the list to the Qml code
    my_model = QStringListModel()
    my_model.setStringList(data_list)
    view.rootContext().setContextProperty("myModel",my_model)

    #Load the QML file
    qml_file = os.path.join(os.path.dirname(__file__),"view.qml")
    view.setSource(QUrl.fromLocalFile(os.path.abspath(qml_file)))

    #Show the window
    if view.status() == QQuickView.Error:
        sys.exit(-1)
    view.show()

    #execute and cleanup
    app.exec_()
    del view

  11. Your application is ready to be run now. Select Projects mode to choose the Python version to run it.

    ../../_images/projectsmode.png

Run the application by using the CTRL+R keyboard shortcut to see if it looks like this:

../../_images/qmlapplication.png

You could also watch the following video tutorial for guidance to develop this application: