**Course Title:** PyQt6 Application Development **Section Title:** Introduction to PyQt6 and Qt Framework **Topic:** Introduction to event-driven programming **Introduction to Event-Driven Programming** ===================================================== Event-driven programming is a paradigm where the flow of a program is determined by events such as user interactions, network requests, or system notifications. In the context of PyQt6, events are used to respond to user interactions with graphical user interface (GUI) components, such as buttons, text boxes, and menus. **Key Concepts** --------------- * **Events**: User actions, system notifications, or other triggers that cause a program to respond. * **Event handlers**: Functions that are executed in response to specific events. * **Event loop**: A mechanism that listens for events and dispatches them to the appropriate event handlers. **How Event-Driven Programming Works in PyQt6** ------------------------------------------------- In PyQt6, events are generated when the user interacts with GUI components. These events are then sent to the event loop, which determines which event handler to execute in response. Event handlers are typically implemented as methods of the widget that triggered the event. **Example: Button Click Event** ------------------------------- Here's a simple example that demonstrates an event-driven programming concept. We'll create a QPushButton and connect its clicked signal to a slot function that displays a message: ```python import sys from PyQt6.QtWidgets import QApplication, QWidget, QPushButton, QLabel, QVBoxLayout from PyQt6.QtCore import pyqtSlot class ButtonClickEvent(QWidget): def __init__(self): super().__init__() self.initUI() def initUI(self): self.setGeometry(100, 100, 400, 300) self.layout = QVBoxLayout() self.setLayout(self.layout) self.button = QPushButton('Click Me!') self.layout.addWidget(self.button) self.button.clicked.connect(self.on_button_click) self.label = QLabel() self.layout.addWidget(self.label) self.show() @pyqtSlot() def on_button_click(self): self.label.setText('Button clicked!') if __name__ == '__main__': app = QApplication(sys.argv) ex = ButtonClickEvent() sys.exit(app.exec()) ``` In this example: * We create a QPushButton and a QLabel in the `initUI` method. * We connect the button's `clicked` signal to the `on_button_click` slot using the `connect` method. * When the button is clicked, the `on_button_click` slot is executed, updating the label's text. **Key Takeaways** ----------------- * PyQt6 applications rely heavily on event-driven programming. * Events are generated by user interactions with GUI components and are dispatched to the event loop. * Event handlers (slots) are used to respond to specific events. * Use the `connect` method to associate a signal with a slot function. **Practical Exercise** --------------------- Try modifying the previous example to create a simple calculator with two QLineEdits for inputting numbers and a QPushButton for triggering the calculation. Connect the button's `clicked` signal to a slot function that retrieves the input values, performs the calculation, and displays the result. **External Resources** ---------------------- For more information on PyQt6's event-driven programming model, see: * [PyQt6 documentation: Signals and Slots](https://doc.qt.io/qtforpython/PySide6/QtCore/Qt.html#PySide6.QtCore.Qt.ConnectionType) * [PyQt6 documentation: Events and Event Filters](https://doc.qt.io/qtforpython/PySide6/QtCore/Qt.html#PySide6.QtCore.Qt.EventLoopPriority) **Leave a Comment** ------------------- If you have any questions or need help with this topic, leave a comment below. Do not hesitate to ask if you have any questions regarding the topic. **Next Topic** -------------- In the next topic, we will cover 'Introduction to core widgets: QPushButton, QLabel, QLineEdit, and more' under the section 'Working with Widgets and Layouts'.