Скачать или смотреть Fixing onlyDigits Boolean Assignment in JavaFX TextField Extensions

Learn how to resolve issues related to boolean property assignment in JavaFX FXML when extending TextField classes. Explore effective solutions and best practices for custom components.
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This video is based on the question https://stackoverflow.com/q/64569165/ asked by the user 'Никита' ( https://stackoverflow.com/u/11341720/ ) and on the answer https://stackoverflow.com/a/64578249/ provided by the user 'James_D' ( https://stackoverflow.com/u/2189127/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

As a beginner diving into JavaFX, you may run into various challenges while developing your graphical user interfaces (GUIs). One common issue that developers encounter involves assigning boolean values to properties in custom classes that extend from existing JavaFX components, like TextField.

In this guide, we'll discuss a specific error that arises when using FXML with a custom TextBox class and how to resolve it quickly. The error message indicates a problem with resolving the onlyDigits property, causing unexpected behavior in your application.

The Problem

When working with a custom class that extends TextField, such as the following TextBox class:

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

You may face an error when trying to define properties in your FXML file, specifically for the onlyDigits property. The error message you might encounter is:

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

The reason for this error lies in the fact that the name of the property onlyDigits starts with the text "on", which the FXML parser misinterprets as an event handler.

Understanding the Root Cause

JavaFX's FXML parser has specific conventions and expectations when interpreting properties. It mistakenly assumes that properties beginning with "on" are event handlers (like onAction). Hence, when you assign a boolean value of true to onlyDigits, it thinks you are trying to point to a function in your FXML script instead, leading to the error.

To illustrate, here's the relevant portion of the FXML where the issue arises:

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

Since onlyDigits appears to be a function to the FXML parser, it causes confusion and results in the LoadException error.

The Solution

To resolve this error, you need to change the name of the onlyDigits property to something that won't trigger the FXML parser's assumptions about event handlers. A suggested alternative is useOnlyDigits.

Step-by-step Instructions to Update Your Code

Rename the Property: Change the boolean property name in your TextBox class to useOnlyDigits.

Update your TextBox class as follows:

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

Modify Your FXML: Update the FXML code to reflect the new property name:

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

By making these changes, the FXML parser will correctly interpret the property as a boolean value rather than attempting to treat it as an event handler.

Conclusion

Name conventions in JavaFX can lead to unexpected errors, especially when creating custom components that extend existing classes. In this case, redefining the property name from onlyDigits to useOnlyDigits provides a clear solution to the FXML parsing issue.

As you continue your journey with JavaFX, keep in mind the importance of adhering to naming conventions to avoid similar pitfalls. Happy coding!