Скачать или смотреть Understanding the Error: Named parameters cannot begin with an underscore in Flutter

Explore the reasons behind the error regarding private variables in Flutter and discover the correct implementation to resolve it.
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Understanding the Error: Named parameters cannot begin with an underscore in Flutter

If you're developing a Flutter application, you may encounter the error message stating that "named parameters cannot begin with an underscore." This can be confusing, especially when you want to create a private variable that is only accessible within a specific file. In this guide, we will dive deep into this issue and provide a clear solution to help you understand how to properly implement private variables in your Dart and Flutter code.

The Problem: Why Does This Error Occur?

In Dart (the programming language used by Flutter), variables that begin with an underscore are considered private. This means that they are only accessible within the file where they are defined. While private variables have their purposes, they cannot be directly used as named parameters in constructors, resulting in the error you may have encountered.

Example of the Problematic Code

Here’s the code that leads to the error message:

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

In this example, the constructor tries to use _appBarTitleColor as a named parameter, which causes the compilation error due to the underscore prefix.

The Solution: Correcting the Implementation

To resolve this issue, you'll need to change how you handle the private variable. Instead of trying to make the private variable a named parameter directly, you can utilize a different approach. Below is the corrected implementation:

Corrected Code Implementation

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

Key Changes Explained

Named Parameter Removed for Private Variable: In the corrected code, the named parameter _appBarTitleColor has been replaced with a public parameter appBarTitleColor. This makes it accessible while allowing you to set the private variable _appBarTitleColor within the constructor's initializer list.

Initializer List: The _appBarTitleColor is initialized to the value passed through the public parameter appBarTitleColor. This lets you still have a private field while controlling its value through the constructor.

Conclusion

When working with Dart and Flutter, understanding the rules surrounding variable visibility is crucial. The specific issue of private variables and named parameters can lead to confusing errors, but knowing how to structure your code correctly can help you avoid these pitfalls. By using a public named parameter to properly initialize a private variable, you can successfully manage scope while keeping your code clean and functional.

If you find yourself struggling with similar errors in the future, always remember: private variables cannot be used as named parameters in constructors. Happy coding!