Basic Widgets and Interaction

In this part, you'll learn how to use some of the core widgets in PySide6—namely, QLabel, QPushButton, and QLineEdit—and how to connect signals (like a button click) to slots (functions) to respond to user actions.

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Step 1: Introduction to the Widgets

• QLabel:
  Displays text or images. In our example, it will show a message to the user.

• QLineEdit:
  Provides a single-line text input where users can type information. We’ll use this to allow the user to enter their name.

• QPushButton:
  A clickable button that triggers actions. We'll connect its click event to a function that reads the input from QLineEdit and updates the QLabel.

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Step 2: Connecting Signals to Slots

In PySide6, widgets emit signals when specific events occur (e.g., when a button is clicked). Slots are functions that are called in response to these signals. In our example, clicking the button will trigger a slot function that updates the label with the text entered in the line edit.

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Step 3: Example Code

Create a Python file (e.g., basic_widgets.py) and add the following code:

import sys
from PySide6.QtWidgets import QApplication, QMainWindow, QWidget, QLabel, QPushButton, QLineEdit, QVBoxLayout
from PySide6.QtCore import Qt

class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("Basic Widgets and Interaction")

        # Create a QLabel to display messages
        self.label = QLabel("Enter your name and press the button")
        self.label.setAlignment(Qt.AlignCenter)

        # Create a QLineEdit for text input
        self.line_edit = QLineEdit()
        self.line_edit.setPlaceholderText("Enter your name")

        # Create a QPushButton that the user will click
        self.button = QPushButton("Submit")
        # Connect the button's clicked signal to a custom slot function
        self.button.clicked.connect(self.on_button_clicked)

        # Set up a vertical layout and add the widgets
        layout = QVBoxLayout()
        layout.addWidget(self.label)
        layout.addWidget(self.line_edit)
        layout.addWidget(self.button)

        # Create a container widget, set the layout, and assign it as the central widget
        container = QWidget()
        container.setLayout(layout)
        self.setCentralWidget(container)

    def on_button_clicked(self):
        # Retrieve text from the line edit
        name = self.line_edit.text()
        if name:
            # Update the label with a greeting message
            self.label.setText(f"Hello, {name}!")
        else:
            # Prompt the user to enter their name if the field is empty
            self.label.setText("Please enter your name.")

# Create the application instance and run the event loop
app = QApplication(sys.argv)
window = MainWindow()
window.show()
sys.exit(app.exec())

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How It Works

1. Creating the Widgets:

   • A QLabel displays the initial message.
   • A QLineEdit allows the user to input their name.
   • A QPushButton is used to submit the input.

2. Layout Management:

   • A QVBoxLayout organizes the widgets vertically.
   • The layout is set on a container QWidget, which becomes the central widget of the main window.

3. Signals and Slots:

   • The button’s clicked signal is connected to the on_button_clicked method.
   • When the button is clicked, on_button_clicked retrieves the text from the QLineEdit and updates the QLabel accordingly.

4. Event Loop:

   • The application starts its event loop with app.exec(), waiting for user interactions.