**Course Title:** PySide6 Application Development **Section Title:** Multithreading and Asynchronous Operations **Topic:** Using QThread and QRunnable for background tasks In the previous topics, we've covered the basics of PySide6 and how to create responsive UIs. However, as we add more features to our applications, we'll inevitably encounter tasks that take a long time to complete. If we perform these tasks directly in the main thread, they will block the UI, making our application unresponsive. In this topic, we'll learn how to use QThread and QRunnable to move these tasks to the background, ensuring that our application stays responsive. **What are QThread and QRunnable?** QThread is a class in Qt that provides a way to run a function in a separate thread. A thread is a separate flow of execution that runs concurrently with the main thread. QRunnable is a class in Qt that represents a function that can be executed in a separate thread. **Why Use QThread and QRunnable?** Using QThread and QRunnable provides several benefits: * **Responsive UI**: By moving long-running tasks to the background, we can ensure that our application's UI remains responsive. * **Efficient resource usage**: We can use QThread and QRunnable to optimize resource usage by running multiple tasks concurrently. **How to Use QThread** To use QThread, you'll need to: 1. Create a new class that inherits from QThread. 2. Override the run() method to perform the desired task. 3. Start the thread using the start() method. Here's a basic example of how to use QThread: ```python import sys from PySide6.QtCore import QThread, Signal from PySide6.QtWidgets import QApplication, QLabel, QPushButton class MyThread(QThread): finished = Signal(str) def run(self): # Perform a long-running task here for i in range(10): print(f"Thread: {i}") self.msleep(1000) self.finished.emit("Thread finished") class MainWindow(QApplication): def __init__(self): super().__init__([]) self.label = QLabel("Press the button to start the thread") self.button = QPushButton("Start Thread") self.button.clicked.connect(self.start_thread) self.label.show() self.button.show() def start_thread(self): self.thread = MyThread() self.thread.finished.connect(self.on_thread_finished) self.thread.start() def on_thread_finished(self, message): print(message) if __name__ == "__main__": app = MainWindow() sys.exit(app.exec()) ``` **How to Use QRunnable** To use QRunnable, you'll need to: 1. Create a new class that inherits from QRunnable. 2. Override the run() method to perform the desired task. 3. Create an instance of QThreadPool and use the start() method to start the task. Here's a basic example of how to use QRunnable: ```python import sys from PySide6.QtCore import QRunnable, QThreadPool, QSignalMapper from PySide6.QtWidgets import QApplication, QLabel, QPushButton class MyRunnable(QRunnable): def run(self): # Perform a long-running task here for i in range(10): print(f"Runnable: {i}") self.setAutoDelete(False) # Prevent auto-deletion QThreadPool.globalInstance().waitForDone(1000) # Simulate sleep class MainWindow(QApplication): def __init__(self): super().__init__([]) self.label = QLabel("Press the button to start the runnable") self.button = QPushButton("Start Runnable") self.button.clicked.connect(self.start_runnable) self.label.show() self.button.show() def start_runnable(self): self.runnable = MyRunnable() QThreadPool.globalInstance().start(self.runnable) if __name__ == "__main__": app = MainWindow() sys.exit(app.exec()) ``` **Best Practices for Using QThread and QRunnable** When using QThread and QRunnable, keep the following best practices in mind: * **Use signals and slots to communicate between threads**: This ensures that data is passed between threads safely and efficiently. * **Avoid shared resources**: Whenever possible, avoid sharing resources between threads to prevent data corruption and other synchronization issues. * **Use the waitForDone() method to wait for a task to finish**: This allows your application to wait for a task to finish without blocking the main thread. **Conclusion** In this topic, we've explored how to use QThread and QRunnable to run background tasks in PySide6. These classes provide a powerful way to optimize resource usage and improve application responsiveness. If you have any questions or need further clarification on any of the concepts covered, feel free to ask for help. In the next topic, we'll be covering how to handle long-running tasks without freezing the UI. Qt documentation: [https://doc.qt.io/qt-6/qthread.html](https://doc.qt.io/qt-6/qthread.html) [https://doc.qt.io/qt-6/qrunnable.html](https://doc.qt.io/qt-6/qrunnable.html) If there is any other question you may have or need further help, please drop a comment below.