Sharing Data between Main Window and Thread in PyQt Applications

Threads are useful for performing tasks without blocking the main window. However, accessing data from the main window within a thread presents a challenge. Let's explore the appropriate method for data sharing using PyQt.

Inefficient Methods:

1. Passing Window Reference to Thread:
While this allows direct access to main window variables, it violates thread safety principles. Widgets are not reentrant and should only be accessed from the main thread.

2. Maintaining Thread-Synchronized Variable Copies:
This method requires frequent data synchronization, leading to code complexity and potential race conditions.

3. Using Global Variables:
Global variables are not recommended in multithreaded environments. Accessing them concurrently can cause unpredictable outcomes.

Recommended Method:

Using Signals and Slots:
This is the recommended approach in PyQt. Signals and slots provide a thread-safe mechanism for communication between threads. The following steps outline how to use signals and slots for data sharing:

1. Create Signal in Worker Thread:

# in worker thread
class Worker(QtCore.QThread):
    ...
    # Create signal named "beep"
    beep = QtCore.pyqtSignal(int)

2. Emit Signal from Worker Thread:

# in worker thread
def run(self):
    ...
    # emit "beep" signal with current count
    self.beep.emit(count)

3. Connect Slot to Signal in Main Window:

# in main window
self.worker = Worker(self.spinbox.value())
self.worker.beep.connect(self.update)  # update槽函数

4. Implement Slot Function in Main Window:

# in main window
def update(self, count):
    ...
    # update GUI elements using count

5. Update Shared Data from Main Window:

# in main window
self.spinbox.valueChanged.connect(self.worker.update_value)  # update_value槽函数

6. Implement Slot Function in Worker Thread:

# in worker thread
class Worker:
    ...
    def update_value(self, value):
        # Update sleep time in worker thread

By following these steps, you can safely and efficiently share data between a thread and the main window in PyQt applications.