Coroutines cancellation got me again

Spent way too much time debugging why my network call wasn't completing. The coroutine was being cancelled before the API response came back.

Turns out I was launching the coroutine in a ViewModel scope, but when the Fragment was detached, the ViewModel's scope was getting cancelled. Which makes sense, but I wasn't expecting it.

The fix? Use viewModelScope.launch with NonCancellable for operations that need to complete regardless of the ViewModel lifecycle, or better yet, use a different scope for long-running operations.

viewModelScope.launch {
    try {
        val result = repository.fetchData()
        _uiState.value = UiState.Success(result)
    } catch (e: Exception) {
        _uiState.value = UiState.Error(e.message)
    }
}

But if you really need something to finish even after the ViewModel is cleared, you might want to use GlobalScope or a custom scope. Though GlobalScope is generally not recommended, sometimes you need it for things like logging or analytics that should complete regardless.

Actually, the better approach is to use lifecycleScope in the Fragment/Activity if you need it tied to the UI lifecycle, or create a custom scope tied to the Application.

Just a reminder to always think about cancellation when working with coroutines. It's one of those things that works great until it doesn't.

Thanks for reading! Check out more posts on the blog if you'd like.