Скачать или смотреть Fixing Flutter/Dart: Getting Directory Contents with Future Not Working

Learn how to efficiently fetch directory contents in Flutter using asynchronous methods. Discover the best practices and solutions to common issues encountered with Futures in Dart.
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This video is based on the question https://stackoverflow.com/q/64090503/ asked by the user 'John Chambers' ( https://stackoverflow.com/u/4569410/ ) and on the answer https://stackoverflow.com/a/64090661/ provided by the user 'Gregory Conrad' ( https://stackoverflow.com/u/10003008/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Fixing Flutter/Dart: Getting Directory Contents with Future Not Working

If you’re diving into Flutter and Dart, encountering issues while fetching directory contents using Futures can be quite daunting. It’s a common problem for developers, especially those new to asynchronous programming. In this guide, we’ll explore one such issue, where the Flutter application fails to display the contents of a directory correctly due to improper handling of Futures. We’ll break down the problem and walk through effective solutions, so you can master the use of Futures in your Flutter applications.

What’s the Problem?

A developer faced a challenge in getting the contents of a directory and displaying it on the screen. The issue occurs when trying to manage a Future within a Future. While the developer was able to retrieve and display data correctly when using a single Future with hardcoded return values, embedding a Future inside another Future led to unexpected behavior: the FutureBuilder didn't wait for the inner Future to complete, resulting in blank outputs until the file list was processed.

Example Code

Here’s a simplified version of the code causing the problem:

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In the above example, the underlying method getFileList() is expected to return the list of files but actually returns immediately without waiting for the Future to resolve.

Understanding the Issue

The primary issue here lies in the usage of .then. Dart’s Future is non-blocking, meaning when you call .then, the execution moves on without waiting for completion. This results in returning an empty list to the FutureBuilder before the actual data is retrieved, which is why the text "Still looking" appears.

Solutions

There are several ways to resolve this issue. Below, I’ll outline the most effective method and two additional alternatives.

Solution 1: Using async/await

The most straightforward and recommended way to handle asynchronous operations in Dart is by utilizing async and await. This method allows your code to pause execution until the Future is resolved, making your asynchronous code easier to read and maintain.

Here’s how you can rewrite the getFileList method:

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Solution 2: Using a Completer

A Completer can provide more control over how and when a Future completes. However, this approach is a bit more complex and may introduce unnecessary boilerplate code, which can negatively impact readability. Here’s a brief overview:

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Solution 3: Fetching Data in initState

For Stateful Widgets, another approach is to make the directory fetching operation in the initState method. This way, you can call setState once the data has been retrieved.

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Conclusion

Understanding how to handle asynchronous programming in Flutter with Futures is a crucial skill for any developer. By switching from .then to using async/await, or employing a Completer, you can effectively manage your Futures and ensure smoother interactions in your apps.

With these tips, you’re well on your way to successfully managing directory contents retrieval in your Flutter applications! Happy coding!