Скачать или смотреть Why Your ArrayList Size Becomes Zero After Calling a Function in Android Development

Struggling with an `ArrayList` that turns to zero in your Android app? Learn the cause and solution to fix this common mistake when filtering data in RecyclerView.
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This video is based on the question https://stackoverflow.com/q/64040268/ asked by the user 'Abu Saeed' ( https://stackoverflow.com/u/13523077/ ) and on the answer https://stackoverflow.com/a/64040492/ provided by the user 'Prateek Srivastava' ( https://stackoverflow.com/u/12519110/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding Your ArrayList Issue in Android Development

If you've been developing Android applications, you might have encountered a frustrating issue: your ArrayList size turns to zero after calling a filtering function. This problem can leave you perplexed, especially if everything seems fine at first glance. In this guide, we'll dissect the problem and provide a clear solution to ensure your array lists work seamlessly when filtering data.

The Problem: ArrayList Size Becomes Zero

In your scenario, you are trying to filter items in a RecyclerView based on user input in an EditText. However, upon typing, you found that your ArrayList size dropped to zero, leaving you with no filtered data to display. You provided some useful code snippets, and let's take a closer look at what might be happening.

Code Breakdown

Let's review the relevant parts of your code to identify the root cause:

ArrayList Declarations:

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

You have three lists involved:

searchItem: Initially filled with media files.

filteredMediaList: Intended to hold filtered results.

mediaList: This points to searchItem directly.

Loading Files:
In your load_Directory_Files_Search method, files are collected and added to searchItem. This works correctly, and you're logging the sizes of your lists to confirm they are populated as expected.

Filter Function Logic:
When you filter in response to text changes, you do the following in the filter() method:

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

This line clears filteredMediaList, but here’s the catch: filteredMediaList, mediaList, and searchItem are all pointing to the same memory location because you did not create new instances for mediaList and filteredMediaList. Consequently, clearing one affects all three.

The Solution: Separate Memory Instances

To resolve this issue, you need to ensure that mediaList and filteredMediaList are new instances and not references to the same memory as searchItem. This way, any changes you make to filteredMediaList won’t inadvertently affect searchItem or mediaList. Here’s how to properly set up the lists in your onCreate method:

Revised Code for onCreate Method

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

Key Changes Made

Instead of directly pointing mediaList and filteredMediaList to searchItem, new instances are created for both. This isolates changes made to one list from affecting the others, resolving the zero size issue.

Conclusion

By understanding how object references work in Java, especially when dealing with ArrayList, you can avoid unexpected behaviors like your array size turning zero after filtering. Remember to create separate instances when you need independent lists. This small change can save you from a lot of debugging frustration down the road. Happy coding!