Styjun

Currently I use a service to make network calls with retrofit but I want to update this model to use ViewModel with LiveData. The thing I am struggling with is how to setup the Repository to update the livedata object.

In the examples I have seen, people return a LiveData wrapped object in the repository something like this

public LiveData<NewsResponse> getData()
 final MutableLiveData<DataResponse> data = new MutableLiveData<>();
 apiService.getData().enqueue(new Callback<DataResponse>() 

 @Override
 public void onResponse(Call<DataResponse> call, Response<DataResponse> response)

 if (response.isSuccessful())
 data.setValue(response.body());
 
 

 @Override
 public void onFailure(Call<DataResponse> call, Throwable t) 
 data.setValue(null);
 
 );
 return data;

then in the ViewModel they would do

private MutableLiveData<DataResponse> dataResponse = new MutableLiveData();
private Repository repository;

public PopularGamesViewModel(@NonNull Application application) 
 repository = new Repository();
 dataResponse = repository.getData();


public MutableLiveData<DataResponse> getData()
 return dataResponse;

Then in the Activity somewhere they would do

viewModel.getData().observe(this, dataResponse -> 
 if (dataResponse != null)
 
 // Do something
 
 );

And the thing that seems wrong to me with that is anytime I want to get new/updated data from the repository a new LiveData object is created so previous observers wont work anymore so I would also have to set the observer again right?

How could you set it up so that you just constantly observe a LiveData object and then from the ViewModel call the repository to get any new data and then the ViewModel updates the LiveData object from the Repository?

Does what I am suggesting make any sense?

As far as I understood your question you want to observe the change in your livedata. for that you might want to refer to MediatorLiveData.

 public LiveData<PagedList<FooPojoList>> liveData;
 private MediatorLiveData<PagedList<FooPojoList>> mediatorLiveData;
 public FooListViewModel(@NonNull Application application) 
super(application);
mediatorLiveData=new MediatorLiveData<>();


public MediatorLiveData<PagedList<FooPojoList>> init(FooDao fooeDao,FooFrom foofrom,String orderBy) 
liveData = new LivePagedListBuilder(fooDao.getAllFooList(sqliteQuery), PAGE).build();
 mediatorLiveData.addSource(liveData, new Observer<PagedList<FooPojoList>>() 
 @Override
 public void onChanged(@Nullable PagedList<FooPojoList> fooListPojos) 
 mediatorLiveData.setValue(fooListPojos);
 
 );
return mediatorLiveData;