Скачать или смотреть Solving the Connectivity Issue: Connecting Signals to QTimer Slots in PySide2

Learn how to effectively connect signals in PySide2, avoid warnings, and create a seamless QTimer execution in your PySide2 applications.
---
This video is based on the question https://stackoverflow.com/q/64024361/ asked by the user 'christophe' ( https://stackoverflow.com/u/13732812/ ) and on the answer https://stackoverflow.com/a/64025164/ provided by the user 'eyllanesc' ( https://stackoverflow.com/u/6622587/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Unable to connect to a Signal sent in a QTimer Slot if Slot is called before connecting the signal

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Solving the Connectivity Issue: Connecting Signals to QTimer Slots in PySide2

When working with PySide2, it's not uncommon to run into issues with signals and slots, especially concerning the timing of when signals are connected. A common problem arises when trying to connect a signal to a slot that might be invoked before the connection is established.

In this guide, we will explore a specific example involving a timer and how to address the issue of signals not being received by a display class in the correct order.

The Problem

You have two classes: one class (MyClock) that emits a signal every second using a timer (QTimer), and another class (ClockDisplay) that is intended to receive and print the emitted time. However, when the timer's signal is emitted before the display class has connected to it, you may encounter warnings and unexpected behavior.

Example Code Causing the Issue

Here's a brief snapshot of the problematic code:

[[See Video to Reveal this Text or Code Snippet]]

In this implementation:

The QTimer calls the Tick slot before establishing the connection to the SEND signal.

This leads to a warning message regarding the order of signals and slots and ultimately results in the SEND signal not being received by the display.

Warning Message

The warning generated indicates that the signals and slots in your MyClock class are not ordered properly, and this may lead to issues. The warning tells us that the Tick() slot was added before the SEND signal, indicating a potential problem.

The Solution

To address this issue, you need to ensure that you connect the signal before starting the timer. Here’s how you can reorganize the code and adopt a modern syntax for defining signals and slots in PySide2.

A Revised Example

Here's the corrected version of your code:

[[See Video to Reveal this Text or Code Snippet]]

Key Changes Made

Signal Declaration: Instead of using the older QtCore.SIGNAL() syntax, we define the SEND signal directly in the class definition. This approach is cleaner and aligns with modern PyQt/PySide standards.

Reordered Initialization: The connection of the SEND signal occurs before starting the timer. This prevents any warnings and ensures the signal is received correctly.

Conclusion

By following the structured approach outlined above, you can effectively mitigate the issues related to signal connectivity in PySide2 applications. Adopting the newer syntax not only cleans up your code but also ensures that signals are managed in a way that avoids warnings and runtime issues.

Next time you are working with signals and slots, remember to connect your signals prior to engaging any timers or events that may trigger them. Happy coding!