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Learn how to effectively combine `TextTheme` styles in Flutter for a Material app while avoiding null safety issues.
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This video is based on the question https://stackoverflow.com/q/75751444/ asked by the user 'Chris Nadovich' ( https://stackoverflow.com/u/10125253/ ) and on the answer https://stackoverflow.com/a/75752017/ provided by the user 'Andrei Volgin' ( https://stackoverflow.com/u/821657/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Combining TextTheme Styles in Flutter: A Simple Guide

When building a Material app with Flutter, you might find yourself in a situation where you want to customize your text styles without reinventing the wheel. Flutter's TextTheme provides a set of predefined text styles, but combining these styles can sometimes be tricky, especially when dealing with null safety. In this post, we'll explore the problem and present a clear solution to effectively use and combine Flutter’s text styles.

The Problem: Need for Customization

You're working on a Flutter app and want to use predefined TextTheme styles like bodyLarge for your text. You encounter the following scenario:

You're able to set the text style to bodyLarge easily:

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

However, you want to emphasize the text. There’s no bodyEmphasized style available, so you attempt to set the font to bold:

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

The real challenge arises when you try to combine both bodyLarge and bold styling:

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This approach results in a null safety error because bodyLarge is nullable. This leads to a few critical questions:

Why are standard text theme styles nullable?

Is there a simple way to make text both larger and emphasized while remaining consistent with standard styles?

Should you handle potential null values in your code, or just forcefully unwrap them with a ! operator?

Understanding the Source of Null Safety Issues

The key to resolving these concerns lies in understanding the underlying structure of Flutter’s TextTheme. The TextTheme styles can either be initialized based on the 2018 or 2021 version used in Flutter. Here’s a critical snippet from the source code that highlights how these styles are managed:

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

From this assertion, it’s evident that the styles become nullable if either the 2018 or 2021 styles are initialized. However, if you opt for the default 2021 styles, you can rely on bodyLarge being non-null, which simplifies the process of text customization.

Solution: Safely Combining Text Styles

To safely combine text styles in Flutter, follow these steps:

Step 1: Opt for the Latest TextTheme

Ensure that you are using the latest version of the TextTheme in your Flutter app, which allows you to avoid dealing with nullable types.

Step 2: Use the copyWith Method Wisely

By using the copyWith method, you can append styles to the existing TextTheme. Here is how you can combine larger and emphasized text safely, assuming you are using the 2021 styles:

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

Step 3: Handle Nullable Styles Gracefully

To avoid null safety issues, you can provide a default value when the style is null. This ensures that your code doesn't crash, and instead uses a fallback style when needed.

Example Implementation

Here’s a complete example of how you might apply this in your Flutter app:

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

Conclusion

Combining text styles in Flutter’s TextTheme can be approached effectively by understanding the implications of null safety. By opting for the latest theme version, you can confidently use copyWith to add custom styles without running into errors. Always remember to handle potential null values gracefully to ensure your app runs smoothly. With these techniques, you'll enhance your Material app's text presentation while leveraging the power of Flutter’s theming system.