**Course Title:** PySide6 Application Development **Section Title:** Widgets, Layouts, and Events **Topic:** Connecting widgets and signals using slots ### Introduction In the previous topics, we've explored the basics of PySide6 widgets, layouts, and events. However, to create a fully functional GUI application, we need to establish connections between widgets and signals. In this topic, we'll delve into the world of signals and slots, a fundamental concept in Qt and PySide6. ### Understanding Signals and Slots In Qt and PySide6, widgets can emit signals when a specific event occurs, such as a button click or a text change. These signals can be connected to slots, which are functions that respond to the signals. Slots are typically methods that perform a specific action when a signal is emitted. Think of signals and slots as a communication system between widgets. When a widget emits a signal, it's like sending a message to other widgets. If another widget has a slot connected to that signal, it will receive the message and respond accordingly. ### Connecting Signals to Slots To connect a signal to a slot, we use the `connect()` method. The syntax is as follows: ```python widget.signal.connect(slot) ``` Here, `widget` is the object that emits the signal, `signal` is the signal being emitted, and `slot` is the function that responds to the signal. ### Example 1: Connecting a QPushButton to a QLabel Let's create a simple example that connects a QPushButton to a QLabel. When the button is clicked, it will emit a signal that updates the label's text. ```python import sys from PySide6.QtWidgets import QApplication, QPushButton, QLabel, QVBoxLayout, QWidget class MyWidget(QWidget): def __init__(self): super().__init__() self.initUI() def initUI(self): layout = QVBoxLayout() self.setLayout(layout) self.label = QLabel("Initial Text") layout.addWidget(self.label) button = QPushButton("Click Me") button.clicked.connect(self.updateLabel) layout.addWidget(button) def updateLabel(self): self.label.setText("Button Clicked") if __name__ == "__main__": app = QApplication(sys.argv) widget = MyWidget() widget.show() sys.exit(app.exec()) ``` In this example, we connect the `clicked` signal of the QPushButton to the `updateLabel` slot. When the button is clicked, the `updateLabel` method is called, which updates the label's text. ### Example 2: Connecting a QLineEdit to a QLabel Let's create another example that connects a QLineEdit to a QLabel. When the text in the QLineEdit changes, it will emit a signal that updates the label's text. ```python import sys from PySide6.QtWidgets import QApplication, QLineEdit, QLabel, QVBoxLayout, QWidget class MyWidget(QWidget): def __init__(self): super().__init__() self.initUI() def initUI(self): layout = QVBoxLayout() self.setLayout(layout) self.label = QLabel("Initial Text") layout.addWidget(self.label) lineEdit = QLineEdit() lineEdit.textChanged.connect(self.updateLabel) layout.addWidget(lineEdit) def updateLabel(self, text): self.label.setText(text) if __name__ == "__main__": app = QApplication(sys.argv) widget = MyWidget() widget.show() sys.exit(app.exec()) ``` In this example, we connect the `textChanged` signal of the QLineEdit to the `updateLabel` slot. When the text in the QLineEdit changes, the `updateLabel` method is called, which updates the label's text. ### Key Concepts * Signals are emitted by widgets when a specific event occurs. * Slots are functions that respond to signals. * Signals and slots are connected using the `connect()` method. * When a signal is emitted, the connected slot is called. ### Practical Takeaways * Use signals and slots to establish connections between widgets. * Use the `connect()` method to connect signals to slots. * Use the `disconnect()` method to disconnect signals from slots. ### Further Reading * [Qt Documentation: Signals and Slots](https://doc.qt.io/qt-5/signalsandslots.html) * [PySide6 Documentation: Signals and Slots](https://doc.qt.io/qtforpython-5/PySide6/QtCore/PySide6.QtCore.Signal.html) **Do you have any questions about connecting widgets and signals using slots? Please leave a comment below.** In the next topic, we'll explore advanced widgets, including QComboBox, QListWidget, QTableWidget, and QTreeView.