In the last Google I/O, Jose Alcerreca and Yigit Boyar told us that we should no longer use LiveData to fetch data. Now we should use suspend functions for one-shot fetches and use Kotlin's Flow to create a data stream. I agree that coroutines are great for one-shot fetching or other CRUD operations, such as inserting, etc. But in cases where I need a data stream, I don’t understand what advantages Flow gives me. It seems to me that LiveData is doing the same.
Example with Flow:
ViewModel
val items = repository.fetchItems().asLiveData()
Repository
fun fetchItems() = itemDao.getItems()
Dao
@Query("SELECT * FROM item")
fun getItems(): Flow<List<Item>>
Example with LiveData:
ViewModel
val items = repository.fetchItems()
Repository
fun fetchItems() = itemDao.getItems()
Dao
@Query("SELECT * FROM item")
fun getItems(): LiveData<List<Item>>
I would also like to see some examples of projects using coroutines and Flow to work with the Room or Retrofit. I found only a Google's ToDo sample where coroutines are used for one-shot fetching and then manually refetch data on changing.
Flow is sort of a reactive stream ( like rxjava ). There are a bunch of different operators like .map, buffer() ( anyway fewer operators compared to rxJava ). So, one of the main differences between LiveData and Flow is that you can execute the map computation / transformation in some other thread using
flowOn(Dispatcher....).
So, for example :-
flowOf("A","B","C").map { compute(it) }.flowOn(Dispatchers.IO).collect {...} // U can change the execution thread of the computation ( by default it is in the same dispatcher as collect )
With LiveData and map , the above can't be achieved directly !
So it is recommended to keep flow in the repository level , and make the livedata a bridge between the UI and the repository !
The main difference is that
flow is not lifecycle aware but liveData is lifecyle aware. ( we can use stateFlow in conjunction with repeatOnLifecycle to make it lifecycle aware )flow has got a bunch of different operators which livedata doesn't have !But again , Its up to u how u wanna construct your project !