Скачать или смотреть Solving the Dismissable Exception in ListView with Flutter

Learn how to fix the common error related to `Dismissable` in `ListView` in Flutter when using index parameters by following this detailed guide.
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This video is based on the question https://stackoverflow.com/q/77048748/ asked by the user 'Caio' ( https://stackoverflow.com/u/15330823/ ) and on the answer https://stackoverflow.com/a/77049482/ provided by the user '聂超群' ( https://stackoverflow.com/u/15057576/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving the Dismissable Exception in ListView with Flutter: A Step-by-Step Guide

Working with Flutter can be a rewarding experience, but it also comes with its share of challenges. One common issue developers face is related to Dismissable widgets inside a ListView. If you're dealing with an exception that states "Invalid value: Valid value range is empty: 0", you’re in the right place. This guide will guide you through understanding the cause of this error and how to fix it effectively.

Understanding the Problem

You may encounter the error "Invalid value: Valid value range is empty: 0" when using the key parameter with Dismissable inside a ListView. This happens when the ListView tries to build an item at an index, but the list it is relying on (in this case, people) is empty at that exact moment.

Key Points Highlighted:

The key for the Dismissable should reference an existing element in the list.

The exception indicates that the list being used is empty, which leads to index issues.

Here’s an example of how your existing implementation might look:

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

The Solution

To solve this issue, you need to introduce a method that checks the size of the people list before rendering the ListView. This way, you can provide a placeholder (like a loading spinner) when the list is empty, preventing the error from occurring.

Step-by-Step Implementation

Create a new private method called _getChild that will manage the logic for displaying your child widget based on the state of people.

Modify the ListView.builder to utilize _getChild.

Here’s how the modified code should look:

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

Summary of Changes

Check for Empty State: The _getChild method checks if the people list is empty and shows a loading indicator if it is.

Prevent the Error: The ListView.builder is only called when the list has items, preventing the exception from being thrown.

Conclusion

By following the steps outlined in this guide, you can address the common issue related to Dismissable widgets inside ListView when using an index as a key. Proper checks on your list state will lead to smoother user experiences and fewer runtime errors. If you have further questions or need clarification, feel free to ask!