Implement Infinite scroll with ViewModel And Retrofit in recyclerview - android-recyclerview

Question

Before adding viewmodel & livedata , i successfully implemented infinity scroll with retrofit. But after adding viewmodel & livedata with Retrofit, My can't update recyclerview with new data call or viewmodel observer not update the list.
I simply want to infinite scrolling as my code does before. I add a global variable to reuse next page token. Am i missing anything or any sample to implement infinite recyclerview with viewmodel & retrofit will be awesome.
public static String NEXT_PAGE_URL = null;
I coded like that.
My Activity -> PlaceListActivity
placeRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
LogMe.d(tag, "onScrollStateChanged:: " + "called");
// check scrolling started or not
if (newState == AbsListView.OnScrollListener.SCROLL_STATE_TOUCH_SCROLL) {
isScrolling = true;
}
}
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
LogMe.d(tag, "onScrolled:: " + "called");
super.onScrolled(recyclerView, dx, dy);
currentItem = layoutManager.getChildCount();
totalItems = layoutManager.getItemCount();
scrolledOutItems = ((LinearLayoutManager) recyclerView.getLayoutManager()).findFirstVisibleItemPosition();
LogMe.d(tag, "currentItem:: " + currentItem);
LogMe.d(tag, "totalItems:: " + totalItems);
LogMe.d(tag, "scrolledOutItems:: " + scrolledOutItems);
if (isScrolling && (currentItem + scrolledOutItems == totalItems)) {
LogMe.d(tag, "view:: " + "finished");
isScrolling = false;
if (ApplicationData.NEXT_PAGE_URL != null) {
LogMe.d(tag, "place adding:: " + " onScrolled called");
ll_loading_more.setVisibility(View.VISIBLE);
// todo: call web api here
callDataFromLocationAPi(type, ApplicationData.NEXT_PAGE_URL, currentLatLng);
} else {
LogMe.d(tag, "next_page_url:: " + " is null");
}
}
}
});
private void callDataFromLocationAPi(String type, String next_page_url, LatLng latLng) {
if (Connectivity.isConnected(activity)) {
showProgressDialog();
model.getNearestPlaces(type, next_page_url, latLng).
observe(activity, new Observer<List<PlaceDetails>>() {
#Override
public void onChanged(#Nullable List<PlaceDetails> placeDetails) {
ll_loading_more.setVisibility(View.GONE);
LogMe.i(tag, "callDataFromLocationAPi: onChanged called !");
hideProgressDialog();
if (placeDetails != null) {
placeDetailsList = placeDetails;
placeListAdapter.setPlaceList(placeDetails);
}
}
});
} else {
showAlertForInternet(activity);
}
}
In PlaceViewModel
public class PlaceViewModel extends AndroidViewModel {
//this is the data that we will fetch asynchronously
private MutableLiveData<List<PlaceDetails>> placeList;
private PlaceRepository placeRepository;
private String tag = getClass().getName();
public PlaceViewModel(Application application) {
super(application);
placeRepository = new PlaceRepository(application);
}
//we will call this method to get the data
public MutableLiveData<List<PlaceDetails>> getNearestPlaces(String type,
String next_page_token,
LatLng latLng) {
//if the list is null
if (placeList == null) {
placeList = new MutableLiveData<>();
//we will load it asynchronously from server in this method
//loadPlaces(type, next_page_token, latLng);
placeList = placeRepository.getNearestPlacesFromAPI(type, next_page_token, latLng);
}
//finally we will return the list
return placeList;
}
}
In my PlaceRepository.java looks
public class PlaceRepository {
private static final Migration MIGRATION_1_2 = new Migration(1, 2) {
#Override
public void migrate(SupportSQLiteDatabase database) {
// Since we didn't alter the table, there's nothing else to do here.
}
};
private PlaceDatabase placeDatabase;
private CurrentLocation currentLocation = null;
private String tag = getClass().getName();
//this is the data that we will fetch asynchronously
private MutableLiveData<List<PlaceDetails>> placeList;
public PlaceRepository(Context context) {
placeDatabase = PlaceDatabase.getDatabase(context);
//addMigrations(MIGRATION_1_2)
placeList =
new MutableLiveData<>();
}
public MutableLiveData<List<PlaceDetails>> getNearestPlacesFromAPI(String type, final String next_page_token, LatLng latLng) {
List<PlaceDetails> placeDetailsList = new ArrayList<>();
try {
ApiInterface apiService = ApiClient.getClient().create(ApiInterface.class);
Call<Example> call = apiService.getNearbyPlaces(type,
latLng.latitude + "," +
latLng.longitude, ApplicationData.PROXIMITY_RADIUS,
ApplicationData.PLACE_API_KEY, next_page_token);
call.enqueue(new Callback<Example>() {
#Override
public void onResponse(Call<Example> call, Response<Example> response) {
try {
Example example = response.body();
ApplicationData.NEXT_PAGE_URL = example.getNextPageToken();
// next_page_url = example.getNextPageToken();
LogMe.i(tag, "next_page_url:" + ApplicationData.NEXT_PAGE_URL);
if (example.getStatus().equals("OK")) {
LogMe.i("getNearbyPlaces::", " --- " + response.toString() +
response.message() + response.body().toString());
// This loop will go through all the results and add marker on each location.
for (int i = 0; i < example.getResults().size(); i++) {
Double lat = example.getResults().get(i).getGeometry().getLocation().getLat();
Double lng = example.getResults().get(i).getGeometry().getLocation().getLng();
String placeName = example.getResults().get(i).getName();
String vicinity = example.getResults().get(i).getVicinity();
String icon = example.getResults().get(i).getIcon();
String place_id = example.getResults().get(i).getPlaceId();
PlaceDetails placeDetails = new PlaceDetails();
if (example.getResults().get(i).getRating() != null) {
Double rating = example.getResults().get(i).getRating();
placeDetails.setRating(rating);
}
//List<Photo> photoReference = example.getResults().
// get(i).getPhotos();
placeDetails.setName(placeName);
placeDetails.setAddress(vicinity);
placeDetails.setLatitude(lat);
placeDetails.setLongitude(lng);
placeDetails.setIcon(icon);
placeDetails.setPlace_id(place_id);
//placeDetails.setPlace_type(place_type_title);
double value = ApplicationData.
DISTANCE_OF_TWO_LOCATION_IN_KM(latLng.latitude, latLng.longitude, lat, lng);
//new DecimalFormat("##.##").format(value);
placeDetails.setDistance(new DecimalFormat("##.##").format(value));
String ph = "";
if (example.getResults().
get(i).getPhotos() != null) {
try {
List<Photo> photos = example.getResults().
get(i).getPhotos();
//JSONArray array = new JSONArray(example.getResults().
//get(i).getPhotos());
//JSONObject jsonObj = new JSONObject(array.toString());
//ph = jsonObj.getString("photo_reference");
ph = photos.get(0).getPhotoReference();
//LogMe.i(tag, "\n" + ph);
} catch (Exception e) {
e.printStackTrace();
//placeDetails.setPicture_reference(ph);
//PLACE_DETAILS_LIST.add(placeDetails);
//LogMe.i(tag, "#### Exception Occureed ####");
ph = "";
//continue;
}
}
placeDetails.setPicture_reference(ph);
placeDetailsList.add(placeDetails);
placeList.postValue(placeDetailsList);
}
} else {
}
} catch (Exception e) {
e.printStackTrace();
}
}
#Override
public void onFailure(Call<Example> call, Throwable t) {
Log.e("onFailure", t.toString());
}
});
} catch (RuntimeException e) {
//hideProgressDialog();
Log.d("onResponse", "RuntimeException is an error");
e.printStackTrace();
} catch (Exception e) {
Log.d("onResponse", "Exception is an error");
}
return placeList;
}
}
I precise code due to question simplicity.

Answer 1

Though you already use android-jetpack, take a look at Paging library. It's specially designed for building infinite lists using RecyclerView.
Based on your source code, I'd say that you need PageKeyedDataSource, here is some example which includes info about how to implement PageKeyedDataSource -
7 steps to implement Paging library in Android
If talking about cons of this approach:
You don't need anymore to observe list scrolling (library doing it for you), you just need to specify your page size in the next way:
PagedList.Config myPagingConfig = new PagedList.Config.Builder()
.setPageSize(50)
.build();
From documentation:
Page size: The number of items in each page.
Your code will be more clear, you'll get rid of your RecyclerView.OnScrollListener
ViewModel code will be shorter, it's will provide only PagedList:
#NonNull
LiveData<PagedList<ReviewSection>> getReviewsLiveData() {
return reviewsLiveData;
}