Скачать или смотреть Solving the @ immutable Error in Flutter: How to Properly Initialize a late Variable in a Widget

Learn how to resolve the `@ immutable` error you may face in Flutter when initializing a `late` variable in your widget. This guide provides a clear solution to keep your code clean and functional.
---
This video is based on the question https://stackoverflow.com/q/71479914/ asked by the user 'Benoît VALLETTE d'OSIA' ( https://stackoverflow.com/u/2810092/ ) and on the answer https://stackoverflow.com/a/71480714/ provided by the user 'salihgueler' ( https://stackoverflow.com/u/1744873/ ) 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: How to init a "late" in a flutter widget without @ immutable error

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.
---
How to Init a late in a Flutter Widget Without @ immutable Error

When working with Flutter, developers often encounter various warnings and errors that can be confusing, especially related to widget immutability. One common issue is the @ immutable error when trying to declare a late variable. If you've found yourself in this situation, you're not alone! In this post, we'll break down the issue and provide a clear solution to avoid these errors while maintaining the functionality of your widget.

Understanding the Problem

Imagine you have a widget defined as a StatefulWidget that receives a list of String items. Here’s the core of the problem presented in your widget:

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

The Error Message

When you attempt to run this code, you might encounter an error like this:

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

This message can be quite perplexing, especially if you are unaware of why it is triggered. Essentially, it tells us that your widget is declared as immutable, but you have a field, scrollerValues, that isn’t declared as final, which leads to the violation of immutability.

The Solution

To resolve the immutability issue related to your late variable, you need to make a slight modification to your code. Specifically, you should declare the scrollerValues as late final. Let’s break down the solution step by step.

Step 1: Use late final for the Variable

Update the declaration of the scrollerValues in your widget like so:

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

Step 2: Explanation of the Key Changes

What Does late Mean?: In Dart, late is used to declare a variable that will be initialized later. It allows you to defer initialization until the variable is actually accessed.

Why Use final?: The final keyword ensures that once the variable scrollerValues is set, it cannot be changed. This is crucial for maintaining the immutability requirement of the widget structure in Flutter.

Step 3: Full Example

Here’s how your updated widget might look in full:

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

Conclusion

Addressing the @ immutable error in Flutter can be simple with a few adjustments. By utilizing the late final declaration for your instance variables in a widget, you can preserve your widget's immutability while maintaining the required flexibility for your internal logic. Now, go ahead and implement these changes in your project and enjoy a smoother coding experience!

If you have any questions or further issues regarding this functionality, feel free to reach out in the comments!