E1 - getting started with PyQT

event loop

• QApplication class is the core of every QT application
• only one instance is needed
• it holds the event loop - the core loop which governs the user interaction with the GUI

image: M Fitzpatrick, Create DUI Applications with Python & Qt6, 6th Edition

• each interaction generates an event, placed on the event queue
• the event handler deals with the event, and passes the control back to the loop to wait for more events

import sys
from PyQt6.QtWidgets import QApplication, QPushButton

## creating an instance of the application
app = QApplication(sys.argv)

## creating an instance of a button
window = QPushButton("Push Me")
window.show() #hidden by default

## start the event loop
app.exec()

• to create custom windows, subclass QMainWindow

## creating a sub class
class MainWindow(QMainWindow):

	##including the setup, allwing the window behviour to be self contained
    def __init__(self):
        super().__init__()

        self.setWindowTitle("My App")
        
        button = QPushButton("Press Me!")
        
        self.setFixedSize(QSize(400, 300)) # set the window size to 400x300 px
        self.setMinimumSize(QSize(200, 300))
        self.setMaximumSize(QSize(600, 300))  

        ## set the central widget of the window.
        self.setCentralWidget(button)
        
        
## assigning the subclass to a variable
window = MainWindow()
window.show()