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Discover how to effectively use two dependent async tasks in a StreamBuilder in Flutter, where the first task fetches friend requests and the second task retrieves profile information.
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This video is based on the question https://stackoverflow.com/q/64230296/ asked by the user 'f10h' ( https://stackoverflow.com/u/14402265/ ) and on the answer https://stackoverflow.com/a/64230757/ provided by the user 'Tirth Patel' ( https://stackoverflow.com/u/4593315/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Use Two Dependent Async Tasks in a StreamBuilder in Flutter

Integrating Firebase with Flutter can be challenging, especially when dealing with multiple asynchronous tasks that depend on one another. This guide will specifically address a common scenario faced by developers: how to use two dependent async tasks in a StreamBuilder.

The Problem at Hand

You have a StreamBuilder that listens to a stream of friend requests from Firebase/Firestore. For each friend request you receive, you need to execute a second async task to fetch the user profile information of the person who sent the request. The challenge arises from the fact that you need to await the second async call before displaying your data, but the StreamBuilder's builder function cannot itself be asynchronous.

Here's the initial approach you might be using, which unfortunately has limitations due to the way asynchronous programming works in Flutter.

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

As you can see, this approach can lead to scenarios where the list is returned before all async tasks complete, thus providing incomplete or empty data.

The Solution

The solution lies in nesting a FutureBuilder inside your StreamBuilder. This allows you to await the result of the second async task while keeping the first async task responsive within your UI. Below, I outline the steps you need to take to implement this.

Step-By-Step Implementation

StreamBuilder Setup: Start by setting up your StreamBuilder to listen for friend requests.

Iterate Through Requests: For each friend request received, create a FutureBuilder to fetch the corresponding user profile.

Handle Future State: Inside the FutureBuilder, handle the different states (loading and success) properly to render your UI correctly.

Here’s how the updated code would look:

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

Important Notes

Performance Impact: Using a FutureBuilder inside a StreamBuilder can lead to multiple network calls for friend profiles. If performance becomes an issue, consider caching profile data where possible.

UI Responsiveness: Make sure to handle loading states to ensure your application provides users with a smooth experience without displaying empty states.

Conclusion

By nesting a FutureBuilder inside your StreamBuilder, you can effectively manage multiple async tasks that depend on each other within your Flutter application. This approach not only makes your code cleaner but also keeps your UI responsive as it handles data fetching in a more structured way.

If you have any questions or additional challenges, feel free to reach out for assistance!