Скачать или смотреть Understanding tkinter Dialogs: Why is Cancel Called When Clicking Ok?

Learn how to correctly manage the behavior of `tkinter` dialogs in your Python applications. Discover why the Cancel function gets called alongside Ok and how to differentiate between them.
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Understanding tkinter Dialogs: Why is Cancel Called When Clicking Ok?

When developing applications in Python using the tkinter library, you may encounter a perplexing issue with dialog windows—specifically, when clicking the "Ok" button often leads to the "Cancel" button being called as well. Many developers have faced this problem, and it raises questions about event handling in tkinter dialogs. In this guide, we aim to unravel the mystery behind this behavior and provide a clear solution to differentiate between the two buttons.

The Problem

You might wonder why clicking the "Ok" button appears to also trigger the "Cancel" button in a tkinter dialog. This can create confusion when you are trying to understand or debug user interactions within your application. The main concern is how to properly manage and identify when each button is pressed.

The Key Question

Why does the Cancel function get called when Ok is clicked, and how can we distinguish between them?

The Source of the Confusion

The confusion primarily arises from how the tkinter library handles events in dialog classes. When you press the "Ok" button, behind the scenes, tkinter is programmed to call the cancel method after the ok method. This behavior is defined in the source code of tkinter, more specifically within the tkinter/simpledialog.py file.

Insights from the Code

In the Dialog class, the ok method includes a try...finally block that calls the self.cancel() method, ensuring that the dialog is properly cleaned up. This means that whenever super().ok() is invoked, it eventually leads to the cancel method being executed regardless of whether "Ok" or "Cancel" was pressed. Here’s how it looks:

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

A Better Solution: Differentiating Between Ok and Cancel

To resolve this issue and accurately determine if "Ok" or "Cancel" was triggered, you can add a simple flag to keep track of which button was pressed. Let’s break it down into a step-by-step approach.

Step 1: Adding a Flag

In your dialog class, you can introduce a boolean attribute that will be set when "Ok" is successfully pressed. If "Cancel" is invoked, you can check this flag to see if "Ok" was called prior.

Step 2: Modify the Code

Here’s how the simplified implementation would look:

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

Explanation

self.oked: A boolean attribute that tracks if the "Ok" button was pressed.

apply Method: Called when "Ok" is pressed, setting self.oked to True and printing a debug message.

cancel Method: Checks this flag. If "Ok" wasn’t pressed before "Cancel," it prints a debug message indicating "Cancel" was called.

Conclusion

By adjusting how you manage the state of your button interactions in tkinter dialogs, you can effectively distinguish between the calls to "Ok" and "Cancel." This knowledge will enhance your tkinter applications, making them more robust and user-friendly. Always remember to check source code for underlying behaviors, as it can significantly illuminate your programming journey.

With this improvement, you should be able to handle dialog interactions in your application efficiently and avoid any confusion regarding button presses in your tkinter interfaces.