Скачать или смотреть Resolving the type '(List Animal ) = Null' Error in Flutter Multi-Select Implementation

Discover how to fix the `type '(List Animal ) = Null' is not a subtype of type '((List Animal? ) = dynamic)?'` error when using the multi-select package in Flutter. Get step-by-step guidance and a clear explanation of the required changes.
---
This video is based on the question https://stackoverflow.com/q/73081264/ asked by the user 'azheen' ( https://stackoverflow.com/u/12742251/ ) and on the answer https://stackoverflow.com/a/73081751/ provided by the user 'tmaihoff' ( https://stackoverflow.com/u/8539278/ ) 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: flutter: type '(List Animal ) = Null' is not a subtype of type '((List Animal? ) = dynamic)?'

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.
---
Introduction

Working with Flutter can be exciting, especially when implementing features that enhance user interactivity, like multi-select options. However, issues can arise - one common error that developers encounter is the type mismatch: type '(List<Animal>) => Null' is not a subtype of type '((List<Animal?>) => dynamic)?'. If you've been stuck with this error while trying to use the MultiSelect package from pub.dev, fear not! In this post, we will provide a detailed solution to fix this issue.

Understanding the Problem

The error you're facing typically occurs when the types you've defined in your code don't match the expected types. In this case, the problem arises due to a mismatch between the expected Animal? type and what your onTap callback is returning.

Scenario

You might be trying to create a list of animals, display them in a multi-select field, and handle the selection through an onTap method. When you copy-paste the example from the documentation and run it, you may get the aforementioned error message.

Steps to Resolve the Error

Here are the steps to correct the error in your multi-select implementation:

1. Update the MultiSelectItem Type

First, ensure that when creating MultiSelectItem instances, you're using the nullable type Animal?. This is where you'll need to modify your list mapping.

Original Code:

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

Updated Code:

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

2. Change the _selectedAnimals List Type

Next, adjust the type of your list that holds the selected animals. It should also be of type Animal?.

Original Code:

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

Updated Code:

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

3. Update the MultiSelectChipField Definition

Make sure that the MultiSelectChipField is also set to accept Animal? types.

Original Code:

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

Updated Code:

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

4. Fix the onTap Callback Argument Type

Finally, ensure that the onTap parameter in the MultiSelectChipField is receiving List<Animal?> instead of List<Animal>.

Original Code:

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

Updated Code:

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

Complete Code Example

Here’s how your complete code should look after making these changes:

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

Conclusion

By following these steps and ensuring that your types are consistent, you can resolve the error and get your multi-select functionality working seamlessly. Always remember that matching variable types can save you a lot of time debugging in Flutter. Happy coding!