PyQt - Action Event

When using PyQt an action event occurs when a user engages with a graphical user interface component linked to a function like clicking a button choosing a menu option or using a keyboard shortcut. Managing these events includes linking these interactions to the functions or procedures that carry out the intended actions.

Key Components of Action Events in PyQt

• QAction − A QAction signifies an activity that the user can initiate. It may be linked to visual interface components, like menu options, toolbar icons and keyboard shortcuts.
• Signal-Slot Mechanism − PyQt uses a signal-slot mechanism to handle events. Signals are emitted when a particular event occurs, and slots are functions or methods that are called in response to those events.
• Event Handlers − PyQt provides predefined event handlers for common user interactions, such as triggered() for when the action is triggered by the user.

Methods for Handling Action Events

Example 1: Simple Button Click Event

In the below example, we'll create a PyQt application with a single button. Clicking the button will trigger an action event that displays a message.

import sys
from PyQt6.QtWidgets import QApplication, QMainWindow, QPushButton, QMessageBox

class MainWindow(QMainWindow):
   def __init__(self):
      super().__init__()

      self.setWindowTitle("Button Click Example")

      button = QPushButton("Click Me!", self)
      button.clicked.connect(self.display_message)

   def display_message(self):
      QMessageBox.information(self, "Message", "Button Clicked!")

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

Output

Example 2: Menu Item Selection Event

In the below example, we'll create a PyQt application with a menu bar. Selecting a menu item will trigger an action event that displays a message.

import sys
from PyQt6.QtWidgets import QApplication, QMainWindow, QMessageBox
from PyQt6.QtGui import QAction

class MainWindow(QMainWindow):
   def __init__(self):
      super().__init__()

      self.setWindowTitle("Menu Selection Example")

      action = QAction("Show Message", self)
      action.triggered.connect(self.display_message)

      menu = self.menuBar()
      file_menu = menu.addMenu("File")
      file_menu.addAction(action)

   def display_message(self):
      QMessageBox.information(self, "Message", "Menu Item Selected!")

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

Output

Example 3: Toggleable Action Event

In the below example, we'll create a PyQt application with a toggleable action. Clicking the action will toggle its state and display a message accordingly.

import sys
from PyQt6.QtWidgets import QApplication, QMainWindow, QMessageBox, QPushButton
from PyQt6.QtGui import QAction

class MainWindow(QMainWindow):
   def __init__(self):
      super().__init__()

      self.setWindowTitle("Toggleable Action Example")

      self.toggle_action = QAction("Toggle", self, checkable=True)
      self.toggle_action.triggered.connect(self.display_message)

      self.addAction(self.toggle_action)

      self.toggle_button = QPushButton("Toggle Action", self)
      self.toggle_button.clicked.connect(self.toggle_action.trigger)

   def display_message(self, checked):
      if checked:
         QMessageBox.information(self, "Message", "Action Checked!")
      else:
         QMessageBox.information(self, "Message", "Action Unchecked!")

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

Output