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A comprehensive guide on using `viewModelScope` in Kotlin to handle asynchronous operations and wait for responses from multiple `suspend functions`.
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How to Wait for Response Values in viewModelScope from Two Suspend Functions

When working with asynchronous programming in Kotlin, particularly in Android development, you may often face the challenge of coordinating multiple asynchronous calls. For instance, you might need to wait for responses from two suspend functions before proceeding with further actions. In this post, we'll explore how to effectively handle such scenarios using viewModelScope.

The Problem

Imagine you have two suspend functions that fetch data asynchronously from a database: fetchName() and fetchSurname(). Your goal is to wait for both these operations to complete before you move on to another function call that requires both values.

Here's a snippet of your current code for context:

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Understanding viewModelScope and Coroutines

When you execute code within a launch block under viewModelScope, it runs within the coroutine context provided. This means that if you use it sequentially without any special mechanisms, code within the block will wait for previous actions to finish before starting new ones.

In your case, the code will only proceed once fetchName() and fetchSurname() have completed because they are both wrapped in withContext(Dispatchers.IO). This is essential to remember as you move forward.

The Solution

To wait for both responses effectively and proceed with another API call, you can simply follow a structured approach:

1. Using withContext

You can maintain your current structure but add your additional logic directly after the suspend functions. This ensures that any further operations, such as making an API call, happen only after both functions return their values. Here’s how the code can be structured:

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2. Using the Main Dispatcher for UI Updates

If you're planning to update UI components with the fetched values, you should switch back to the Main dispatcher as below:

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3. An Alternative: Using Flow

As an alternative method, consider using Flow to create a reactive stream of data that can handle changes and updates. This can be particularly useful if you're dealing with continuous updates or streams of data rather than one-off calls.

Conclusion

Handling asynchronous operations in Kotlin with viewModelScope can be straightforward when you understand the coroutine execution flow. By wrapping your calls to fetchName() and fetchSurname() effectively within a coroutine context, you can ensure that your subsequent calls only happen after the required data is ready.

Now, you can confidently wait for responses from multiple suspend functions without running into the pitfalls of asynchronous programming. Happy coding!