When working with coroutines in Android, you might encounter scenarios where you want to exit early—for example, if cached data is available, avoiding unnecessary network calls. In this tutorial, we'll explore how to cleanly exit a lifecycleScope.launch block when a certain condition is met (e.g., data exists in the database).

1. The Problem: Unnecessary Execution

Consider this common scenario:

  1. Check if data exists in a local database (e.g., Room, Paper, etc.).
  2. If found, process it and skip the network call.
  3. If not found, proceed with downloading.

A naive implementation might look like this: 

lifecycleScope.launch {
    val fromDB = getFromDB() // Returns Result<T>
    fromDB.onSuccess { data ->
        processResult(data)
        showData()()
    }
    fromDB.onFailure { 
        // Proceed with download
    }

    // This still executes even if we got data from DB!
    val result = downloadFile()
    // ... handle download
}

Problem: Even if we get data from the DB, the downloadFile() call still executes, wasting resources.

2. Solution: Early Exit with return@launch

To exit the coroutine early when we have the data, we use return@launch: 

lifecycleScope.launch {
    val fromDB = getFromDB()
    fromDB.onSuccess { data ->
        processResult(data)
        showData()()
        return@launch  // ← Exits the coroutine here
    }
    // Only reaches here if DB fetch failed
    val result = downloadFile()
    // ... handle download
}

✅ Key Benefit: The coroutine stops immediately after return@launch, preventing unnecessary work.

3. Alternative Approaches

*A. Using when with Result (More Explicit)

If you prefer structured control flow: 

lifecycleScope.launch {
    when (val result = getFromDB()) {
        is Result.Success -> {
            processResult(result.value)
            showData()()
            return@launch
        }
        is Result.Failure -> { /* Proceed */ }
    }

    val downloadResult = downloadFile()
    // ... handle download
}

B. Using runCatching (Kotlin-Style Error Handling)

If your getFromDB() throws exceptions: 

lifecycleScope.launch {
    runCatching { getFromDB() }
        .onSuccess { data ->
            processResult(data)
            showData()()
            return@launch
        }

    val downloadResult = downloadFile()
    // ... handle download
}

4. Best Practices

  1. Avoid Side Effects

  2. Ensure return@launch doesn’t break expected behavior (e.g., leaving resources open).

  3. Use Named Lambdas for Clarity

  4. If working with nested coroutines, label them for better readability: 

lifecycleScope.launch(dispatcher) outerScope@ {
    someOperation().onSuccess {
        return@outerScope // Exits the outer coroutine
    }
}

  1. Consider also/let for Chaining

  2. If you need to perform an action before exiting: 

lifecycleScope.launch {
    getFromDB()
        .onSuccess { data ->
            processResult(data)
            showData()()
        }
        .also { if (it.isSuccess) return@launch }  // Exits after processing

    downloadFile()
}

5. Last word

Using return@launch inside lifecycleScope.launch provides a clean way to exit early when a condition is met (e.g., cached data is available). This improves efficiency by avoiding unnecessary operations.

Key Takeaways:

✔ Use return@launch to exit a coroutine early.
✔ Prefer structured error handling (Result, runCatching, when).
✔ Ensure cleanup logic isn’t skipped unintentionally.

Would you like me to expand on any part? Let me know in the comments! 🚀