Скачать или смотреть Fixing the Future dynamic to Stream PostModel Error in Flutter with BLoC

Learn how to resolve the `Future dynamic ` is not a subtype of `Stream PostModel ` error in your Flutter projects using the BLoC pattern and RxDart.
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This video is based on the question https://stackoverflow.com/q/68301217/ asked by the user 'VDTe' ( https://stackoverflow.com/u/10797617/ ) and on the answer https://stackoverflow.com/a/68301444/ provided by the user 'Hemal Moradiya' ( https://stackoverflow.com/u/15275305/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving the Future<dynamic> is not a subtype of Stream<PostModel>? Error in Flutter

If you've been developing a Flutter application using the BLoC (Business Logic Component) pattern and RxDart, you might have encountered an error that states: "type 'Future<dynamic>' is not a subtype of type 'Stream<PostModel>?'." This issue can be frustrating, especially when you're trying to display data from an API in your Flutter app. In this guide, we'll dive into the root cause of this error and how to solve it step-by-step.

Understanding the Problem

The error occurs when there's a mix-up between Futures and Streams in your BLoC implementation. A Future represents a single asynchronous result, while a Stream is used for a sequence of data over time.

Common Scenarios for the Error

Misusing Sink and Stream: Your BLoC may incorrectly convert data to a stream.

Incorrect Data Types: The data type in your model and API response does not match.

Missing Return in Asynchronous Functions: Not returning the expected data after API calls can lead to the app trying to use incorrect data types.

Let's Examine the Code

We have the following snippets with issues leading to the error:

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In this case, the code erroneously uses fetchPosts() as a stream source for the StreamBuilder, when it actually returns a Future.

The Solution

Step 1: Correcting the Stream Source

Instead of calling fetchPosts() directly within the StreamBuilder, you should access a properly defined stream that emits data. Here’s how you can fix this:

Change the StreamBuilder to Use the Stream

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Step 2: Triggering Data Fetching

You need to call the fetchPosts() method at an appropriate time, ideally in the initState() method of your stateful widget. Here’s how to do it:

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Step 3: Fixing the Model Data Type

Next, ensure that your model reflects the data structure you're getting from the API. The API response is a list, so you need to adjust the PostModel as follows:

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Step 4: Make Sure to Return Data in fetchPosts()

Lastly, ensure that your fetchPosts() method returns the PostModel. Here’s the updated version:

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

Conclusion

By following these steps, you can effectively resolve the Future<dynamic> is not a subtype of type 'Stream<PostModel>' error. This not only ensures that your app runs smoothly but also helps you better understand the use of Futures and Streams in Flutter when using the BLoC pattern.

If you found this guide helpful, don't hesitate to share it with fellow developers or leave a comment with your thoughts. Happy coding!