Android: kotlin coroutine background task

Question

I have a method

fun refrehList() {
    viewModelScope.launch {
        myData.value = withContext(Dispatchers.Default) {
            summaryRepository.getSummaries(true)
        }
        allData.value = withContext(Dispatchers.Default) {
            SummaryRepository.getSummaries(false)
        }
    }
}

Is this correct way of using coroutine. Is the DB operation happening in the background scope

Answer 1

If you're using Room, its documentation states the following:

You can add the suspend Kotlin keyword to your DAO methods to make them asynchronous using Kotlin coroutines functionality. This ensures that they cannot be executed on the main thread.

So you will be safe calling your repository inside the viewModelScope without changing context.

You can find that Room's documentation section here.

Answer 2

Yes this code will run on separate thread but one after another. Also you should be using Dispatchers.IO for database calls instead of Dispatchers.Default See Io vs Default.

viewModelScope.launch {
        myData.value = withContext(Dispatchers.IO) {
           Log.e("thread1", Thread.currentThread().name)
            summaryRepository.getSummaries(true)
        }
         Log.e("thread2", Thread.currentThread().name)
        allData.value = withContext(Dispatchers.IO) {
           Log.e("thread3", Thread.currentThread().name)
            SummaryRepository.getSummaries(false)
        }
    }

This will print something like :-

E/thread: DefaultDispatcher-worker-1
E/thread2: main
E/thread3: DefaultDispatcher-worker-1

If you want to run those co-routine in parallel you can use async-await .