- Qt 5.15
- Qt Designer Manual
- Using a Designer UI File in Your Qt for Python Application
- Qt 5.15.17 Reference Documentation

Using a Designer UI File in Your C++ Application ◦ Using Custom Widgets with Qt Designer

# Using a Designer UI File in Your Qt for Python Application

## Converting the Form to Python Code

To demonstrate, we use the Qt Widgets animation easing example.

The application consists of one source file, `easing.py`, a UI file `form.ui`, a resource file `easing.qrc` and the project file, `easing.pyproject` file in the YAML format:

     {
         "files": ["easing.qrc", "ui_form.py", "easing.py", "easing_rc.py",
                   "form.ui"]
     }

The UI file is converted to Python code building the form using the User Interface Compiler (uic):

     uic -g python form.ui > ui_form.py

Since the top level widget is named `Form`, this results in a Python class named `Ui_Form` being generated. It provides a function `setupUi()`, taking the widget as parameter, which is called to create the UI elements:

     from ui_form import Ui_Form
     ...
     class Window(QtWidgets.QWidget):
         def __init__(self, parent=None):
             super(Window, self).__init__(parent)

             self.m_ui = Ui_Form()
             self.m_ui.setupUi(self)

Later on, the widgets can be accessed via the `Ui_Form` class:

     self.m_ui.graphicsView.setScene(self.m_scene)

Besides `setupUi()`, `Ui_Form` provides another method `retranslateUi()`, which can be called in reaction to a QEvent of type QEvent.LanguageChange, which indicates a change in the application language.

### The UiTools Approach

The QUiLoader class provides a form loader object to construct the user interface at runtime. This user interface can be retrieved from any QIODevice, e.g., a QFile object. The QUiLoader::load() function constructs the form widget using the user interface description contained in the file.

It is demonstrated by the uiloader example:

     from PySide2.QtUiTools import QUiLoader

     if __name__ == '__main__':
         # Some code to obtain the form file name, ui_file_name
         app = QApplication(sys.argv)
         ui_file = QFile(ui_file_name)
         if not ui_file.open(QIODevice.ReadOnly):
             print("Cannot open {}: {}".format(ui_file_name, ui_file.errorString()))
             sys.exit(-1)
         loader = QUiLoader()
         widget = loader.load(ui_file, None)
         ui_file.close()
         if not widget:
             print(loader.errorString())
             sys.exit(-1)
         widget.show()
         sys.exit(app.exec_())