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PyQt QMainWindow

Summary: in this tutorial, you’ll learn how to use the PyQt QMainWindow to create the main window of an application.

Introduction to the PyQt QMainWindow

So far, you have learned how to use QWidget to create the main window for applications. The QWidget works fine for simple applications but doesn’t support common features of full-blown desktop applications like menu bars, toolbars, and status bars.

PyQt provides you with QMainWindow that support a menu bar, toolbars, and status bar out of the box. So instead of subclassing the QWidget class, you can create the main window by inheriting it from the QMainWindow class like this:

class MainWindow(QMainWindow):Code language: Python (python)

PyQt divides the QMainWindow widget into some sections as shown in the following picture:

QMainWindow Layout

Note that you should not set a layout for the QMainWindow. If you do so, you’ll break the preset arrangement of the widgets.

Set the central widget

A QMainWindow has one and only one central widget. To set a widget as a central widget, you use the setCentralWidget() method of the QMainWindow object.

For example, the following uses the setCentralWidget() method to set the QTextEdit as the central widget:

self.setCentralWidget(QTextEdit())Code language: Python (python)

Set the window title

To set the title for the main window, you use the setWindowTitle() method. For example:

self.setWindowTitle('Editor')Code language: PHP (php)

Set the window icon

To set the icon for the window, you use the setWindowIcon() method. For example:

 self.setWindowIcon(QIcon('./assets/editor.png'))Code language: PHP (php)

In this example:

  • First, create a QIcon and pass in the image path ./assets/editor.png
  • Second, pass the QIcon object to the setWindowIcon() method to set the icon for the window.

Set the geometry for the main window

The geometry defines the coordinate of the window (x,y) or (top, left) and the window’s width and height:

To set the geometry for the window, you use the setGeometry() method of the QMainWindow object. For example, the following uses the setGeometry() method to set the geometry for the window:

self.setGeometry(100, 100, 500, 300)Code language: CSS (css)

In this example, the window will appear at (100, 100) with a width of 500px and height of 300px:

The following program creates the main window using the QMainWindow, sets the central widget, and the window’s title, icon, and geometry:

import sys
from PyQt6.QtWidgets import QApplication, QMainWindow, QTextEdit, QToolBar, QStatusBar
from PyQt6.QtGui import QIcon, QAction


class MainWindow(QMainWindow):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        self.setWindowTitle('Editor')
        self.setWindowIcon(QIcon('./assets/editor.png'))
        self.setGeometry(100, 100, 500, 300)

        self.text_edit = QTextEdit(self)
        self.setCentralWidget(self.text_edit)

        self.show()


if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = MainWindow()
    sys.exit(app.exec())

Adding a menu bar

To add a menu bar to the main window, you use the menuBar() method of the QMainWindow:

menu_bar = self.menuBar()Code language: Python (python)

The menuBar() method returns a QMenuBar object. If a QMenuBar object doesn’t exist, the menuBar() will create a new QMenuBar object before returning it. Otherwise, it returns the existing QMenuBar object.

By default, the menu bar is empty. To add a menu to a menu bar, you use the addMenu() method. For example, the following adds three submenus File, Edit, and Help:

file_menu = menu_bar.addMenu('&File')
edit_menu = menu_bar.addMenu('&Edit')
help_menu = menu_bar.addMenu('&Help')Code language: Python (python)

The addMenu() method returns a QMenu object that represents a drop-down submenu. The string that we pass to the addMenu() method is for labeling the menu in the menu bar.

The character & will underscore the character of the menu label when you press the ALT key. For example, &File will underscore the letter F.

Action

To add menu items to a menu, you need to create actions. An action is an object of the QAction class that represents the functionality of the application.

An action object requires a name and a callback to function properly. In addition, an action may contain an icon and a keyboard shortcut.

To create an action, you can call the addAction() method of a QMenu. For example, the following adds three actions to the File menu:

file_menu.addAction('New', lambda: self.text_edit.clear())
file_menu.addAction('Open', lambda: print('Open'))
file_menu.addAction('Exit', self.destroy)Code language: PHP (php)

If you click the New menu item, the QTextEdit widget will clear all contents. Similarly, by clicking the Open menu item, you’ll see a message on the console, and clicking the Exit menu will end the program.

Also, you can create a QAction object and connects its triggered signal to a slot. For example, the following creates undo and redo actions and adds them to the Edit menu:

undo_action = QAction(QIcon('./assets/undo.png'), 'Undo', self)
undo_action.setShortcut('Ctrl+Z')
undo_action.triggered.connect(self.text_edit.undo)
edit_menu.addAction(undo_action)

redo_action = QAction(QIcon('./assets/redo.png'), 'Redo', self)
redo_action.setShortcut('Ctrl+Y')
redo_action.triggered.connect(self.text_edit.redo)
edit_menu.addAction(redo_action)Code language: Python (python)

Note that the undo and redo actions have icons and keyboard shortcuts.

The following program shows how to add a menu bar and menu items to the File and Edit menus:

import sys
from PyQt6.QtWidgets import QApplication, QMainWindow, QTextEdit, QToolBar, QStatusBar
from PyQt6.QtGui import QIcon, QAction


class MainWindow(QMainWindow):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        self.setWindowTitle('Editor')
        self.setWindowIcon(QIcon('./assets/editor.png'))
        self.setGeometry(100, 100, 500, 300)

        self.text_edit = QTextEdit(self)
        self.setCentralWidget(self.text_edit)

        # setting menu
        menu_bar = self.menuBar()

        file_menu = menu_bar.addMenu('&File')
        edit_menu = menu_bar.addMenu('&Edit')
        help_menu = menu_bar.addMenu('&Help')

        file_menu.addAction('New', lambda: self.text_edit.clear())
        file_menu.addAction('Open', lambda: print('Open'))
        file_menu.addAction('Exit', self.destroy)

        undo_action = QAction(QIcon('./assets/undo.png'), 'Undo', self)
        undo_action.setShortcut('Ctrl+Z')
        undo_action.triggered.connect(self.text_edit.undo)
        edit_menu.addAction(undo_action)

        redo_action = QAction(QIcon('./assets/redo.png'), 'Redo', self)
        redo_action.setShortcut('Ctrl+Y')
        redo_action.triggered.connect(self.text_edit.redo)
        edit_menu.addAction(redo_action)

        self.show()


if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = MainWindow()
    sys.exit(app.exec())

Output:

Adding a toolbar

A toolbar is a bar of icons and/or text that expose the most commonly used function of the application. To add a toolbar to the application:

  • First, create a new QToolBar object.
  • Second, add the toolbar to the application using the addToolbar() method of the QMainWindow.

For example, the following creates a new toolbar and adds it to the application:

toolbar = QToolBar('Main toolbar')
self.addToolBar(toolbar)Code language: Python (python)

To add an item to the toolbar, you use the addAction() method of the QToolBar object. For example:

toolbar.addAction(undo_action)
toolbar.addAction(redo_action)Code language: Python (python)

The following program shows add a toolbar with the undo and redo actions:

import sys
from PyQt6.QtWidgets import QApplication, QMainWindow, QTextEdit, QToolBar
from PyQt6.QtGui import QIcon, QAction


class MainWindow(QMainWindow):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        self.setWindowTitle('Editor')
        self.setWindowIcon(QIcon('./assets/editor.png'))
        self.setGeometry(100, 100, 500, 300)

        self.text_edit = QTextEdit(self)
        self.setCentralWidget(self.text_edit)

        # setting menu
        menu_bar = self.menuBar()

        file_menu = menu_bar.addMenu('&File')
        edit_menu = menu_bar.addMenu('&Edit')
        help_menu = menu_bar.addMenu('&Help')

        file_menu.addAction('New', lambda: self.text_edit.clear())
        file_menu.addAction('Open', lambda: print('Open'))
        file_menu.addAction('Exit', self.destroy)

        undo_action = QAction(QIcon('./assets/undo.png'), 'Undo', self)
        undo_action.setShortcut('Ctrl+Z')
        undo_action.triggered.connect(self.text_edit.undo)
        edit_menu.addAction(undo_action)

        redo_action = QAction(QIcon('./assets/redo.png'), 'Redo', self)
        redo_action.setShortcut('Ctrl+Y')
        redo_action.triggered.connect(self.text_edit.redo)
        edit_menu.addAction(redo_action)

        # adding a toolbar
        toolbar = QToolBar('Main toolbar')
        self.addToolBar(toolbar)

        toolbar.addAction(undo_action)
        toolbar.addAction(redo_action)

        self.show()


if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = MainWindow()
    sys.exit(app.exec())Code language: Python (python)

Adding a status bar

A status bar is a bar located at the bottom of the main window. Typically, a status bar displays short text messages and/or informational widgets.

To add a status bar to the application, you create a QStatusBar object and set it to the main window using the setStatusBar() method:

status_bar = QStatusBar()
self.setStatusBar(status_bar)Code language: Python (python)

The statusBar() method of the QMainWindow returns a QStatusBar object. It will create a new QStatusBar object if the status bar doesn’t exist.

To display a short message, you use the showMessage() method of the QStatusBar object:

status_bar.showMessage('Awesome Editor v1.0')Code language: Python (python)

Or you can directly use the QStatusBar object returned by the statusBar() method of the main window:

self.status_bar.showMessage('Awesome Editor v1.0')Code language: Python (python)

The following program shows a status bar:

import sys
from PyQt6.QtWidgets import QApplication, QMainWindow, QTextEdit, QToolBar, QStatusBar
from PyQt6.QtGui import QIcon, QAction


class MainWindow(QMainWindow):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        self.setWindowTitle('Editor')
        self.setWindowIcon(QIcon('./assets/editor.png'))
        self.setGeometry(100, 100, 500, 300)

        self.text_edit = QTextEdit(self)
        self.setCentralWidget(self.text_edit)

        # setting menu
        menu_bar = self.menuBar()

        file_menu = menu_bar.addMenu('&File')
        edit_menu = menu_bar.addMenu('&Edit')
        help_menu = menu_bar.addMenu('&Help')

        file_menu.addAction('New', lambda: self.text_edit.clear())
        file_menu.addAction('Open', lambda: print('Open'))
        file_menu.addAction('Exit', self.destroy)

        undo_action = QAction(QIcon('./assets/undo.png'), 'Undo', self)
        undo_action.setShortcut('Ctrl+Z')
        undo_action.triggered.connect(self.text_edit.undo)
        edit_menu.addAction(undo_action)

        redo_action = QAction(QIcon('./assets/redo.png'), 'Redo', self)
        redo_action.setShortcut('Ctrl+Y')
        redo_action.triggered.connect(self.text_edit.redo)
        edit_menu.addAction(redo_action)

        # adding a toolbar
        toolbar = QToolBar('Main toolbar')
        self.addToolBar(toolbar)

        toolbar.addAction(undo_action)
        toolbar.addAction(redo_action)

        # status bar
        self.status_bar = QStatusBar()
        self.setStatusBar(self.status_bar)
        self.status_bar.showMessage('Awesome Editor v1.0')

        self.show()


if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = MainWindow()
    sys.exit(app.exec())
Code language: Python (python)

Output:

Summary

  • Use the QMainWindow class to create the main window for the application.
  • Use the setWindowTitle() method to set the title.
  • use the setWindowIcon() method to set the window’s icon.
  • Use the setGeometry() method to set the window’s geometry including the (top, left) coordinates, width, and height.
  • Use the menuBar() method to add a menu bar to the main window.
  • use the setToolBar() method to set a toolbar for the main window.
  • Use the statusBar() method to add a status bar to the main window.
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