在添加viewmodel和livedata之前，我成功实现了无穷滚动并进行了翻新。但是在使用Retrofit添加viewmodel和livedata之后，我无法使用新数据调用来更新recyclerview，或者viewmodel观察器无法更新列表。
我只是想像我的代码之前那样无限滚动。我添加了一个全局变量以重用下一页标记。我是否缺少任何东西或任何样本来使用viewmodel和改造来实现无限的recyclerview会很棒。
public static String NEXT_PAGE_URL = null;
我这样编码。
我的活动-> 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);
}
}
在PlaceViewModel中
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;
}
}
在我的PlaceRepository.java中看起来
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;
}
}
由于问题简单，我编写了精确的代码。
答案 0 :(得分：1)
尽管您已经使用android-jetpack，但请看一下Paging library。它是专为使用RecyclerView构建无限列表而设计的。
根据您的源代码，我想您需要PageKeyedDataSource，下面是一些示例，其中包含有关如何实现PageKeyedDataSource的信息-
7 steps to implement Paging library in Android
如果谈论这种方法的缺点：
您不再需要观察列表滚动（图书馆为您完成），您只需要以以下方式指定页面大小即可：
PagedList.Config myPagingConfig = new PagedList.Config.Builder()
.setPageSize(50)
.build();
摘自文档：
页面大小：每页中的项目数。
您的代码将更加清晰，您将摆脱RecyclerView.OnScrollListener
ViewModel代码将更短，仅提供PagedList：
@NonNull
LiveData<PagedList<ReviewSection>> getReviewsLiveData() {
return reviewsLiveData;
}