Скачать или смотреть Understanding the ProviderNotFoundException in Flutter's Bloc: Separating Bloc Providers

Dive into why separating Bloc Providers in Flutter causes a `ProviderNotFoundException` and learn how to resolve it effectively.
---
This video is based on the question https://stackoverflow.com/q/75122373/ asked by the user 'Gwhyyy' ( https://stackoverflow.com/u/18670641/ ) and on the answer https://stackoverflow.com/a/75180645/ provided by the user 'Cavin Macwan' ( https://stackoverflow.com/u/15638854/ ) 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: Why putting bloc providers in a separate file/class throws an error?

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 the ProviderNotFoundException in Flutter's Bloc

When working with Flutter and the Bloc pattern, you might encounter an error that's both common and perplexing. Imagine this scenario: you have successfully implemented Bloc providers directly within your widget. However, the moment you try to transfer these providers to a separate class, you are met with a frustrating ProviderNotFoundException. Why does this happen, and how can you resolve it? Let’s break it down in detail.

The Problem: What Leads to the Error?

Initial Code that Works

You have a working implementation where you provide your Bloc like this:

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

This setup runs smoothly, reflecting your bloc logic accurately.

The Relocation of Providers

You decide to improve readability by moving your provider list out into a dedicated class:

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

Here is the code in the BlocProviders class:

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

But suddenly, you are greeted with the following error when you run your application:

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

The Solution: Why Separating Causes Issues

Understanding MultiBlocProvider

The problem arises due to how MultiBlocProvider expects its providers argument. This widget takes a list of type BlocProviderSingleChildWidget, which is a mixin defined on SingleChildWidget.

Here’s Why Your Code Fails:

You defined BlocProviders.blocs() to return a List<BlocProvider>, which does not match the expected type BlocProviderSingleChildWidget.

Consequently, the error is thrown because the BlocBuilder cannot find the correct provider for ExampleCubit.

A Working Alternative

One user found a workaround by defining a getter instead of a static function, thus eliminating any type constraints. Here’s how to modify your BlocProviders class:

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

By doing this, you can retain your class structure while allowing flexibility for types, thus bypassing the error.

Additional Tips

Read Documentation: Always refer to the official documentation or source code for MultiBlocProvider to clarify expected types.

Debugging: To troubleshoot similar errors, examine the provider types you are using and ensure they match what your widgets expect.

Conclusion

In summary, moving Bloc providers into a separate file can lead to a ProviderNotFoundException due to type mismatches in Flutter’s MultiBlocProvider. Adjusting how you declare the return type of your providers can help resolve this issue while maintaining code clarity. With these insights, you're now better equipped to handle and debug your Flutter applications involving Bloc.

Remember, programming often involves solving such problems, so don’t get disheartened if you encounter them – there's usually a clear pathway to resolution. Happy coding!