liveData with Coroutines

[isfaaghyth]

Hi! who already use for this one androidx.lifecycle:lifecycle-livedata-ktx:2.2.0-alpha01 ? I've tried it into my repository layer but doesn't work (i'm using retrofit 2.6.0). this is my code:

interface Service {
     @GET("/data")
     suspend fun getData(): Data
}

class Repository @Inject constructor(val service: Service) {
     fun getData(): LiveData<Data> = liveData {
          val data = service.getData()
          emit(data)
     }
}

and this is my viewmodel:

...
     fun fetch() {
          viewModelScope.launch {
              val data = repository.getData()
              println(data.value)
          }
     }
...

the result is null.

any idea about this?
thanks!

[alexkazancew]

Hi @isfaaghyth . Your liveData from repository.getData() don`t have active observers. So liveData not emiting data. Try something this.

...
     fun fetch():LiveData<Data> {
         return repository.getData(viewModelScope)
          }
     }
...

class Repository @Inject constructor(val service: Service) {
     fun getData(scope:CoroutineScope): LiveData<Data> = liveData(scope.coroutineContext) {
          val data = service.getData()
          emit(data)
     }
}

 class SomeFragment:Fragmet(){
    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? { ...
        viewModel.fetch().observe(viewLifecycleOwner, Observer{
                 println(it)
      }
  }
}

P.S.
Correct me if something is wrong

[isfaaghyth]

so, which a good way for my case? @alexkazancew

[alexkazancew]

@isfaaghyth i update my previous answer

[isfaaghyth]

it works! thanks @alexkazancew

[GuilhE]

How about usingliveData{... emit()}while using SavedStateHandle? Is there any benefit?
Here's my SO question

[alexkazancew]

@GuilhE I think you can do something like this

class SomeViewModel(private val savedStateHandle: SavedStateHandle) : ViewModel() {

    companion object {
        private const val PAGE_KEY = "page_key"
    }

    private val _page = MutableLiveData<PageId>(savedStateHandle.get(PAGE_KEY))

    private val _itemLiveData = Transformations.switchMap(_page) { pageId -> repository.getNextPage(pageId) }
    val itemLiveData: LiveData<MyItem> = _itemLiveData

    suspend fun nextPage(pageId: PageId) {
        _page.postValue(pageId)
    }

    override fun onCleared() {
        super.onCleared()
        savedStateHandle.set(PAGE_KEY, _page.value)
    }
}

Let me know if it helped you.