Скачать или смотреть How to Avoid the Same null Check in Kotlin for Filtering Data

Discover effective techniques to simplify your Kotlin code by avoiding duplicate null checks when filtering lists. Learn how to implement cleaner, more readable solutions!
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This video is based on the question https://stackoverflow.com/q/76228722/ asked by the user 'Vivek Modi' ( https://stackoverflow.com/u/8266651/ ) and on the answer https://stackoverflow.com/a/76228777/ provided by the user 'Jorn' ( https://stackoverflow.com/u/8681/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Avoid the Same null Check in Kotlin for Filtering Data

Working with nullable types in Kotlin can often lead to repetitive checks for null values. This can become cumbersome, especially when dealing with lists that may contain empty or null elements. In this post, we will tackle a common problem: how to filter a list of nullable objects without repeating the same null check.

Understanding the Challenge

Let's say you are working with data coming from a server that includes a list of categories, each of which may include a movie object. Here’s a simplified version of the data structure:

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In your code, you want to filter out the categories and movies where the movie name is either null or empty. The traditional way to handle this would require you to check for these conditions more than once, leading to redundancy:

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The Problematic Line

The line that says FilterMovie(movie.name.orEmpty()) requires you to call orEmpty() on the movie name, which checks for null again. This redundancy can make your code harder to read and maintain.

The Solution

Fortunately, there are cleaner ways to handle this filtering process that avoid the repetitive null check. Let's analyze two alternative methods.

Method 1: Using map and filterNot

You can modify your function to call orEmpty() first on the name, and filter out any blank results in one go:

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How It Works

map { it.movie?.name.orEmpty() }: This extracts the movie name or returns an empty string if it's null.

.filterNot { it.isBlank() }: This filters out blank names effectively.

map { FilterMovie(it) }: Finally, it converts the non-blank names directly into FilterMovie instances.

Method 2: Using mapNotNull and let

For a more concise (though slightly less readable) approach, you can use a combination of mapNotNull and let:

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

How It Works

item.movie?.name: Fetches the movie name, maintaining cleanliness.

takeIf { it.isNotBlank() }: This will return the name if it's not blank; otherwise, it skips the let block.

let { FilterMovie(it) }: Converts the validated name into a FilterMovie object if the conditions are met.

Conclusion

By implementing these approaches, you can effectively eliminate redundant null checks in Kotlin while keeping your code clean and easy to follow. Choose the method that best fits your coding style and the needs of your project.

If you have more questions about Kotlin or need further assistance with nullable types, feel free to ask!