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 PySide2 Python packages.

• Qt Creator v4.9 beta1 or later from http://download.qt.io.

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:

   

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

   

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.

   

   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:

   
   #!/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.

   
   #!/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.

   
   #!/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.

   
   #!/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.

    
    #!/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.

    

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

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

Related information

• QML Reference

• QML Integration Tutorial