Скачать или смотреть Resolving the void Return Type Error in Dart with Effective List Filtering

Learn how to address the `void` return type error in Dart and Flutter while efficiently filtering items from a list based on multiple conditions.
---
This video is based on the question https://stackoverflow.com/q/72906446/ asked by the user 'Sasitha Dilshan' ( https://stackoverflow.com/u/10083812/ ) and on the answer https://stackoverflow.com/a/72906533/ provided by the user 'Kaushik Chandru' ( https://stackoverflow.com/u/17169037/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: The return type 'void' isn't a 'FutureOr Iterable _ ', as required by the closure's context

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding and Solving the void Return Type Error in Dart

Dart, the programming language used by Flutter, can sometimes present us with challenging error messages that can be confusing, especially when working with collections. One such error message is: "The return type 'void' isn't a 'FutureOr Iterable _ ', as required by the closure's context." This usually occurs when you attempt to manipulate a list in a way that isn't valid within the current context.

In this guide, we will explore this specific error message, understand its origins, and provide a clear solution to help you efficiently filter items from a list in Dart.

The Problem: What Causes the Error?

Let’s dive into the situation that led to this error. Here's a piece of code that’s commonly encountered in Flutter applications when dealing with state management and collection filtering:

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

In this snippet, we are trying to filter a collection named bank based on a user's input (value). The current setup works perfectly; items are correctly filtered out based on their names.

However, the developer wanted to take it a step further—removing items from the filtered list based on an additional condition. They attempted to use the removeWhere() method like this:

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

This is where the error arises. The method removeWhere() returns void, and trying to chain it after toList() causes the confusion. In this case, Dart is expecting a FutureOr<Iterable<_>>, which is not being returned.

The Solution: Combining Conditions

Fortunately, there is a clean solution to the problem—combining conditions within the where() clause. This avoids the need for additional list manipulation methods like removeWhere(). Here’s how it can be done effectively:

Updated Code

You can achieve the desired functionality by including both conditions directly within the where() method:

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

Explanation:

Combination of Conditions: Instead of filtering the list first and then removing items, you combine the conditions within the where() method. Here’s what happens:

The first condition checks if the bank item’s name contains the value (ignoring case).

The second condition ensures that the item does not have a code of '7788'.

Resulting List: The resulting list will only include items that fulfill both criteria and will therefore not contain any items with the code '7788' or any names matching the input's value.

Conclusion

By understanding how to manipulate lists effectively in Dart and combining filtering conditions, you can write cleaner, more efficient code without running into type-related errors. The updated approach leverages Dart’s powerful collection methods while ensuring type safety and maintaining clarity in your code.

For any further questions about list manipulation or error handling in Dart and Flutter, feel free to drop your queries in the comments below!