Solving Async Future Promise Issues in Swift 5 for Firebase Integration

Learn how to troubleshoot and effectively implement async function calls with Combine framework in Swift 5, specifically for Firebase user fetching.
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Troubleshooting Async Future Promise Issues in Swift 5 for Firebase Integration

When working with asynchronous functions in Swift, especially with frameworks like Combine, it's easy to run into issues where your function doesn't seem to behave as expected. One such common problem is encountered by developers when trying to fetch user data from Firebase and populate an array using Future and Promise. This could lead to receiving an empty result, which is frustrating.

In this guide, we'll explore a specific issue, understand the underlying concepts, and provide a comprehensive solution to ensure your async calls work as intended.

The Problem

Imagine you're trying to load user data asynchronously from Firebase, utilizing the Combine framework's Future and Promise functionalities. The intent is to populate an array with groupMate objects based on user attributes for further processing. However, an unexpected problem arises: your receiveCompletion and receiveValue callbacks do not get called, leading to an empty array being returned.

Here's the summary of the scenario:

You're making async calls to fetch user data.

You're getting an empty array as a result when you expect populated data.

You suspect issues related to your use of AnyCancellable and Future promises.

Understanding the Core Issue

The core issue often arises from the timing of operations in asynchronous programming. If you return before all the asynchronous calls have been completed, your result will not contain the expected data. This scenario is exacerbated when you're looping through multiple async operations and waiting for results before proceeding.

Solution Breakdown

To fix the problem and ensure all groupMates are populated, we’ll make a few adjustments to your implementation. Below are the step-by-step instructions:

Step 1: Fetch Users in Parallel

Instead of just triggering separate futures without managing their completion, we need to collect the results of all futures before calling the completion handler. Here’s how to do it:

Collect all the Future calls in an array.

Use Publishers.MergeMany to combine them into a single publisher that emits values when all futures complete.

Step 2: Update the Implementation

Here’s an updated implementation of the loadUserFromFirebase function to use Publishers.MergeMany:

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

Step 3: Finalize the Group Creation

In your creategroup function, call the adjusted loadUserFromFirebase and expect properly populated data now:

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

Additional Consideration: Use Swift 5.5 Modern Features

If you are targeting iOS 15 and later, consider using the new Swift async/await model, which simplifies working with asynchronous code significantly.

Conclusion

By structuring your futures appropriately and making sure you combine the results correctly, you can avoid getting an empty array from your Firebase queries. Asynchronous programming can indeed be challenging, but with careful implementation, you can harness its full potential in Swift.

Feel free to implement the changes above and watch your async operations flourish!