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Represent firestore data into List view [duplicate]

I wanted to know how to load more data in recylcer view using firestore.
Query query = FirebaseFirestore.getInstance()
.collection("ie").limit(5);
adapter=new InterviewAdapter(this,query);
recyclerView.setAdapter(adapter);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
Adapter class looks like this:
public class InterviewAdapter extends FireStoreAdapter<InterviewAdapter.ViewHolder> {
public interface OnInterviewSelectedListener {
void onInterviewSelected(DocumentSnapshot interview);
}
private InterviewAdapter.OnInterviewSelectedListener mListener;
public InterviewAdapter(Query query, OnInterviewSelectedListener listener) {
super(query);
mListener = listener;
}
#Override
public InterviewAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
LayoutInflater inflater = LayoutInflater.from(parent.getContext());
return new InterviewAdapter.ViewHolder(inflater.inflate(R.layout.ie, parent, false));
}
#Override
public void onBindViewHolder(InterviewAdapter.ViewHolder holder, int position) {
holder.bind(getSnapshot(position), mListener);
}
static class ViewHolder extends RecyclerView.ViewHolder {
TextView title,companyName,username,views,isHired;
public ViewHolder(View itemView) {
super(itemView);
title= (TextView) itemView.findViewById(R.id.title);
companyName= (TextView) itemView.findViewById(R.id.companyName);
username= (TextView) itemView.findViewById(R.id.username);
views= (TextView) itemView.findViewById(R.id.views);
isHired= (TextView) itemView.findViewById(R.id.isHired);
}
public void bind(final DocumentSnapshot snapshot,
final OnInterviewSelectedListener listener) {
InterviewExperience experience;
String companyName=snapshot.getString("companyName");
boolean isHired=Boolean.valueOf(snapshot.getBoolean("isHired"));
String username=snapshot.getString("username");
long views=new Double(Double.valueOf(snapshot.getDouble("views"))).longValue();
String id=snapshot.getId();
String title=snapshot.getString("title");
experience=new InterviewExperience(id,title,companyName,username,isHired,views,null,null);
this.title.setText(experience.getTitle());
this.companyName.setText("Company Name: "+experience.getCompanyName());
this.isHired.setText("Hired: "+experience.isHired());
this.views.setText("Views: "+experience.getViews()+"");
this.username.setText("Created By: "+experience.getUsername());
// Click listener
itemView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
if (listener != null) {
listener.onInterviewSelected(snapshot);
}
}
});
}
}
}
public abstract class FireStoreAdapter<VH extends RecyclerView.ViewHolder>
extends RecyclerView.Adapter<VH>
implements EventListener<QuerySnapshot> {
private static final String TAG = "FirestoreAdapter";
private Query mQuery;
private ListenerRegistration mRegistration;
private ArrayList<DocumentSnapshot> mSnapshots = new ArrayList<>();
public FireStoreAdapter(Query query) {
mQuery = query;
}
#Override
public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {
if (e != null) {
Log.w(TAG, "onEvent:error", e);
onError(e);
return;
}
// Dispatch the event
Log.d(TAG, "onEvent:numChanges:" + documentSnapshots.getDocumentChanges().size());
for (DocumentChange change : documentSnapshots.getDocumentChanges()) {
switch (change.getType()) {
case ADDED:
onDocumentAdded(change);
break;
case MODIFIED:
onDocumentModified(change);
break;
case REMOVED:
onDocumentRemoved(change);
break;
}
}
onDataChanged();
}
public void startListening() {
if (mQuery != null && mRegistration == null) {
mRegistration = mQuery.addSnapshotListener(this);
}
}
public void stopListening() {
if (mRegistration != null) {
mRegistration.remove();
mRegistration = null;
}
mSnapshots.clear();
notifyDataSetChanged();
}
public void setQuery(Query query) {
// Stop listening
stopListening();
// Clear existing data
mSnapshots.clear();
notifyDataSetChanged();
// Listen to new query
mQuery = query;
startListening();
}
#Override
public int getItemCount() {
return mSnapshots.size();
}
protected DocumentSnapshot getSnapshot(int index) {
return mSnapshots.get(index);
}
protected void onDocumentAdded(DocumentChange change) {
mSnapshots.add(change.getNewIndex(), change.getDocument());
notifyItemInserted(change.getNewIndex());
}
protected void onDocumentModified(DocumentChange change) {
if (change.getOldIndex() == change.getNewIndex()) {
// Item changed but remained in same position
mSnapshots.set(change.getOldIndex(), change.getDocument());
notifyItemChanged(change.getOldIndex());
} else {
// Item changed and changed position
mSnapshots.remove(change.getOldIndex());
mSnapshots.add(change.getNewIndex(), change.getDocument());
notifyItemMoved(change.getOldIndex(), change.getNewIndex());
}
}
protected void onDocumentRemoved(DocumentChange change) {
mSnapshots.remove(change.getOldIndex());
notifyItemRemoved(change.getOldIndex());
}
protected void onError(FirebaseFirestoreException e) {};
protected void onDataChanged() {}
}
I used Firestore Adapter code which was given in samples of firestore documentation. Can anyone tell how to use the query object to load more data?
How to load the next 5 items in the recycler view when users scrolls to the end of the list?

You can paginate your Query's result using Query's methods like, startAt(), startAfter(), endAt(), endBefore() with a specified DocumentSnapshot.
If I considered your collection is called "interviews", you can add a method to your FireStoreAdapter like this:
private void paginate(final DocumentSnapshot last, final int limit) {
final Query subset;
if (last == null) {
subset = db.collection("interviews")
.limit(limit);
} else {
subset = db.collection("interviews")
.startAfter(last)
.limit(limit);
}
setQuery(subset);
}
You can perserve the last DocumentSnapshot within onEvent():
final List<DocumentChange> changes = documentSnapshots.getDocumentChanges();
final DocumentSnapshot lastDocument = changes.get(changes.size() - 1).getDocument();
Finally, when users scrolls to the end of the list:
paginate(lastDocument, 5);
And onDocumentAdded() will take care of it. Be carfure NOT to use startAt() because it will not execlude the last one (that already at the end of your list, and will duplicate it).

LiveData isn't being observed properly (gets null) when using Android Pagination Library

I am trying to update the UI depending on whether the data is being loaded or has loaded but it is not working properly. I am using enum class for different states.
Initially the error was
Attempt to invoke virtual method 'void androidx.lifecycle.LiveData.observe(androidx.lifecycle.LifecycleOwner, androidx.lifecycle.Observer)' on a null object reference
Then I passed an empty new MutableLiveData()<>. Now, it doesn't crashes the application, however, the getDataStatus() observer isn't working correctly. Kindly look at my implementations and see if they are right.
DataSource
public class ArticlesDataSource extends PageKeyedDataSource<Integer, NewsItem> {
private static final int FIRST_PAGE = 1;
private static final String TAG = "ArticlesDataSource";
public static final String SORT_ORDER = "publishedAt";
public static final String LANGUAGE = "en";
public static final String API_KEY = Utils.API_KEY;
public static final int PAGE_SIZE = 10;
private String mKeyword;
private MutableLiveData<DataStatus> dataStatusMutableLiveData = new MutableLiveData<>();
public ArticlesDataSource(String keyword) {
mKeyword = keyword;
dataStatusMutableLiveData = new MutableLiveData<>();
}
public MutableLiveData<DataStatus> getDataStatusMutableLiveData() {
return dataStatusMutableLiveData;
}
#Override
public void loadInitial(#NonNull LoadInitialParams<Integer> params, #NonNull LoadInitialCallback<Integer, NewsItem> callback) {
dataStatusMutableLiveData.postValue(DataStatus.LOADING);
NewsAPI newsAPI = ServiceGenerator.createService(NewsAPI.class);
Call<RootJsonData> call = newsAPI.searchArticlesByKeyWord(mKeyword, SORT_ORDER, LANGUAGE, API_KEY, FIRST_PAGE, PAGE_SIZE);
call.enqueue(new Callback<RootJsonData>() {
#Override
public void onResponse(Call<RootJsonData> call, Response<RootJsonData> response) {
if (response.body() != null) {
callback.onResult(response.body().getNewsItems(), null, FIRST_PAGE + 1);
dataStatusMutableLiveData.postValue(DataStatus.LOADED);
}
}
#Override
public void onFailure(Call<RootJsonData> call, Throwable t) {
Log.d(TAG, "onFailure: " + t.getMessage());
dataStatusMutableLiveData.postValue(DataStatus.ERROR);
}
});
}
#Override
public void loadBefore(#NonNull LoadParams<Integer> params, #NonNull LoadCallback<Integer, NewsItem> callback) {
NewsAPI newsAPI = ServiceGenerator.createService(NewsAPI.class);
Call<RootJsonData> call = newsAPI.searchArticlesByKeyWord(mKeyword, SORT_ORDER, LANGUAGE, API_KEY, FIRST_PAGE, PAGE_SIZE);
call.enqueue(new Callback<RootJsonData>() {
#Override
public void onResponse(Call<RootJsonData> call, Response<RootJsonData> response) {
// if the current page is greater than one
// we are decrementing the page number
// else there is no previous page
Integer adjacentKey = (params.key > 1) ? params.key - 1 : null;
if (response.body() != null) {
// passing the loaded data
// and the previous page key
callback.onResult(response.body().getNewsItems(), adjacentKey);
}
}
#Override
public void onFailure(Call<RootJsonData> call, Throwable t) {
Log.d(TAG, "onFailure: " + t.getMessage());
}
});
}
#Override
public void loadAfter(#NonNull LoadParams<Integer> params, #NonNull LoadCallback<Integer, NewsItem> callback) {
NewsAPI newsAPI = ServiceGenerator.createService(NewsAPI.class);
Call<RootJsonData> call = newsAPI.searchArticlesByKeyWord(mKeyword, SORT_ORDER, LANGUAGE, API_KEY, params.key, PAGE_SIZE);
call.enqueue(new Callback<RootJsonData>() {
#Override
public void onResponse(Call<RootJsonData> call, Response<RootJsonData> response) {
dataStatusMutableLiveData.postValue(DataStatus.LOADED);
if (response.code() == 429) {
// no more results
List<NewsItem> emptyList = new ArrayList<>();
callback.onResult(emptyList, null);
}
if (response.body() != null) {
// if the response has next page
// incrementing the next page number
Integer key = params.key + 1;
// passing the loaded data and next page value
if (!response.body().getNewsItems().isEmpty()) {
callback.onResult(response.body().getNewsItems(), key);
}
}
}
#Override
public void onFailure(Call<RootJsonData> call, Throwable t) {
Log.d(TAG, "onFailure: " + t.getMessage());
dataStatusMutableLiveData.postValue(DataStatus.ERROR);
}
});
}
}
DataSourceFactory
public class ArticlesDataSourceFactory extends DataSource.Factory {
private final MutableLiveData<ArticlesDataSource> itemLiveDataSource;
private String mQuery;
private final LiveData<DataStatus> dataStatusLiveData = Transformations.switchMap(itemLiveDataSource, (itemDataSource) -> {
return itemDataSource.getDataStatusMutableLiveData();
});
public ArticlesDataSourceFactory() {
mQuery = "news";
itemLiveDataSource = new MutableLiveData<>();
}
#Override
public DataSource<Integer, NewsItem> create() {
ArticlesDataSource itemDataSource = new ArticlesDataSource(mQuery);
itemLiveDataSource.postValue(itemDataSource);
// dataStatusMutableLiveData = itemDataSource.getDataStatusMutableLiveData();
return itemDataSource;
}
public MutableLiveData<ArticlesDataSource> getArticlesLiveDataSource() {
return itemLiveDataSource;
}
public void setQuery(String query) {
mQuery = query;
}
public MutableLiveData<DataStatus> getDataStatusMutableLiveData() {
return dataStatusMutableLiveData;
}
public void setDataStatusMutableLiveData(DataStatus dataStatus){
dataStatusMutableLiveData.postValue(dataStatus);
}
public LiveData<DataStatus> getDataStatusLiveData() {
return dataStatusLiveData;
}
}
ViewModel
public class ArticlesViewModel extends ViewModel {
public LiveData<PagedList<NewsItem>> itemPagedList;
private MutableLiveData<ArticlesDataSource> liveDataSource;
private ArticlesDataSourceFactory articlesDataSourceFactory;
private LiveData dataStatus = new MutableLiveData<>();
public ArticlesViewModel() {
articlesDataSourceFactory = new ArticlesDataSourceFactory();
liveDataSource = articlesDataSourceFactory.getArticlesLiveDataSource();
dataStatus = articlesDataSourceFactory.getDataStatusMutableLiveData();
PagedList.Config pagedListConfig =
(new PagedList.Config.Builder())
.setEnablePlaceholders(false)
.setPageSize(10).build();
itemPagedList = (new LivePagedListBuilder(articlesDataSourceFactory, pagedListConfig)).build();
}
public void setKeyword(String query) {
if (query.equals("") || query.length() == 0)
articlesDataSourceFactory.setDataStatusMutableLiveData(DataStatus.EMPTY);
else {
articlesDataSourceFactory.setQuery(query);
refreshData();
}
}
void refreshData() {
if (itemPagedList.getValue() != null) {
itemPagedList.getValue().getDataSource().invalidate();
}
}
public LiveData<DataStatus> getDataStatus() {
return dataStatus;
}
}
Fragment
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View rootView = inflater.inflate(R.layout.fragment_articles, container, false);
mContext = getActivity();
progressBar = rootView.findViewById(R.id.progress_circular);
emptyStateTextView = rootView.findViewById(R.id.empty_view);
swipeRefreshLayout = rootView.findViewById(R.id.swipe_refresh);
textViewTitle = rootView.findViewById(R.id.text_view_top_headlines);
recyclerView = rootView.findViewById(R.id.recycler_view);
if (savedInstanceState != null) {
keyword = savedInstanceState.getString("keyword");
}
initEmptyRecyclerView();
articlesViewModel = ViewModelProviders.of(this).get(ArticlesViewModel.class);
articlesViewModel.itemPagedList.observe(getViewLifecycleOwner(), new Observer<PagedList<NewsItem>>() {
#Override
public void onChanged(PagedList<NewsItem> newsItems) {
adapter.submitList(newsItems);
// TODO: Handle UI changes
// handleUIChanges(newsItems);
}
});
articlesViewModel.getDataStatus().observe(getViewLifecycleOwner(), new Observer<DataStatus>() {
#Override
public void onChanged(DataStatus dataStatus) {
switch (dataStatus) {
case LOADED:
progressBar.setVisibility(View.GONE);
emptyStateTextView.setVisibility(View.INVISIBLE);
swipeRefreshLayout.setRefreshing(false);
textViewTitle.setVisibility(View.VISIBLE);
break;
case LOADING:
progressBar.setVisibility(View.VISIBLE);
swipeRefreshLayout.setRefreshing(true);
textViewTitle.setVisibility(View.INVISIBLE);
emptyStateTextView.setVisibility(View.INVISIBLE);
break;
case EMPTY:
progressBar.setVisibility(View.GONE);
swipeRefreshLayout.setRefreshing(false);
textViewTitle.setVisibility(View.INVISIBLE);
emptyStateTextView.setVisibility(View.VISIBLE);
emptyStateTextView.setText(R.string.no_news_found);
break;
case ERROR:
progressBar.setVisibility(View.GONE);
swipeRefreshLayout.setRefreshing(false);
textViewTitle.setVisibility(View.INVISIBLE);
emptyStateTextView.setVisibility(View.VISIBLE);
emptyStateTextView.setText(R.string.no_internet_connection);
break;
}
}
});
swipeRefreshLayout.setOnRefreshListener(() -> {
articlesViewModel.setKeyword(keyword);
});
setHasOptionsMenu(true);
return rootView;
}
DataStatus
public enum DataStatus {
ERROR,
LOADING,
LOADED,
EMPTY
}

When you call invalidate(), a new datasource will be created by the factory. However, you are directly exposing the data status liveData of the "current" created datasource, without taking into consideration that more will be created in the future.
The solution is to store the current data source in the factory in a MutableLiveData, and expose the "most recent current data status" using switchMap.
public class ArticlesDataSourceFactory extends DataSource.Factory {
private final MutableLiveData<ArticlesDataSource> itemLiveDataSource = new MutableLiveData<>();
private String mQuery = "news";
private final LiveData<DataStatus> dataStatusLiveData = Transformations.switchMap(itemLiveDataSource, (itemDataSource) -> {
return itemDataSource.getDataStatusMutableLiveData();
});
public ArticlesDataSourceFactory() {
}
#Override
public DataSource<Integer, NewsItem> create() {
ArticlesDataSource itemDataSource = new ArticlesDataSource(mQuery);
itemLiveDataSource.postValue(itemDataSource);
...
public LiveData<DataStatus> getDataStatusLiveData() {
return dataStatusLiveData;
}

not able to display inner child nodes value in recycler view

before down voting please consider this i have searched everywhere and not found the solution please help..
from the above structure i want to access the values inside Results -> examId> total_marks, marks_scored but i am not being able to get inside Result node
i want the values to be feed inside recyclerview
This is my adapter
public class MarksListAdapter extends RecyclerView.Adapter<MarksListAdapter.MyViewHolder> {
Context context;
ArrayList<MarksList> marksListArrayList;
public MarksListAdapter(Context c, ArrayList<MarksList> p) {
context = c;
marksListArrayList = p;
}
#NonNull
#Override
public MyViewHolder onCreateViewHolder(#NonNull ViewGroup viewGroup, int i) {
return new MyViewHolder(LayoutInflater.from(context).inflate(R.layout.marks_list, viewGroup, false));
}
#Override
public void onBindViewHolder(#NonNull MyViewHolder myViewHolder, int i) {
myViewHolder.tvStudentName.setText(marksListArrayList.get(i).getName());
myViewHolder.tvOutOf_List.setText(marksListArrayList.get(i).getResults().getTotal_marks());
myViewHolder.etEnterMarks.setText(marksListArrayList.get(i).getResults().getMarks_scored());
POJO class
public class MarksList {
String name;
public MarksList() {
}
public MarksList(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
private Results Results;
public com.hitech.hitechacademy.POJO.Results getResults() {
return Results;
}
}
public class Results {
String marks_scored;
String total_marks;
public Results() {
}
public Results(String marks_scored, String total_marks) {
this.marks_scored = marks_scored;
this.total_marks = total_marks;
}
public String getMarks_scored() {
return marks_scored;
}
public void setMarks_scored(String marks_scored) {
this.marks_scored = marks_scored;
}
public String getTotal_marks() {
return total_marks;
}
public void setTotal_marks(String total_marks) {
this.total_marks = total_marks;
}
}
both are seperate java classes
This is the recyclerview activity
DatabaseReference examRef = firebaseDatabase.getReference().child("Batches").child(batchNameValue);
examRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
String examTitle;
String studentName;
specificStudent.clear();
resultsArrayList.clear();
for (DataSnapshot studentResult : dataSnapshot.getChildren()) {
examTitle = (String) studentResult.child("Results").child(examKeyValue).child("exam_name").getValue();
Log.d("TAG_Full", examTitle + "" + examFullName);
if (examTitle != null && examTitle.equals(examFullName)) {
MarksList marksList = studentResult.getValue(MarksList.class);
//studentName = (String) studentResult.child("name").getValue();
specificStudent.add(marksList);
Log.d("SpecificStudent", specificStudent.toString() + resultsArrayList.toString());
} else {
//code for 1 exam and no students
}
}
specificStudent.toString();
marksListAdapter = new MarksListAdapter(LoadedExam.this,specificStudent);
marksRecyclerView.setAdapter(marksListAdapter);
marksListAdapter.notifyDataSetChanged();
}
I am not getting any errors but only the name of the student is getting fetched Please help

List<ParseUser> .contains ParseUser always FALSE

I have an if statement written below:
//Set Friend Action OnClickListener & Image
if (ParseUser.getCurrentUser().getList("friendsArray").contains(searchResultsList.get(position))) {
Glide.with(holder.imgFriendAction.getContext()).load(R.drawable.ic_phone_black_24dp).into(holder.imgFriendAction);
ImageViewCompat.setImageTintList(holder.imgFriendAction, ColorStateList.valueOf(searchContext.getColor(R.color.green)));
}
else if (ParseUser.getCurrentUser().getList("pendingFriendsArray").contains(searchResultsList.get(position))) {
Glide.with(holder.imgFriendAction.getContext()).load(R.drawable.ic_check_black_24dp).into(holder.imgFriendAction);
ImageViewCompat.setImageTintList(holder.imgFriendAction, ColorStateList.valueOf(searchContext.getColor(R.color.gray_dark)));
}
else {
Glide.with(holder.imgFriendAction.getContext()).load(R.drawable.ic_person_add_black_24dp).into(holder.imgFriendAction);
ImageViewCompat.setImageTintList(holder.imgFriendAction, ColorStateList.valueOf(searchContext.getColor(R.color.colorPrimary)));
}
The problem is that every single time I run that statement it always returns FALSE for both if statements even though I know for a fact that 'friendsArray' & 'pendingFriendsArray' return TRUE in many circumstances.
Both arrays contain pointers to the _User table.
searchResultsList is declared as follows:
private List<ParseUser> searchResultsList;
I've logged all three items (friendsArray, pendingFriendsArray & searchResultsList.get(position)) to the console and they show the following:
D/friendsArray: [com.parse.ParseUser#ae66779, com.parse.ParseUser#8371cbe, com.parse.ParseUser#32d511f, com.parse.ParseUser#5fd2c6c, com.parse.ParseUser#7dd0235, com.parse.ParseUser#9c446ca, com.parse.ParseUser#5fe03b]
D/pendingFriendsArray: [com.parse.ParseUser#7c6a358, com.parse.ParseUser#3688cb1, com.parse.ParseUser#480596]
D/searchResultsList.get(position) =: com.parse.ParseUser#5fe03b
The entire class is below:
public class SearchUserAdapter extends RecyclerView.Adapter<SearchUserAdapter.ViewHolder> {
private Context searchContext;
private List<ParseUser> searchResultsList;
OnItemClickListener onItemClickListener;
public SearchUserAdapter(Context context, List<ParseUser> dataSet) {
searchContext = context;
searchResultsList = dataSet;
}
public interface OnItemClickListener {
public void onItemClick(View view, ParseUser searchUserObject, int position);
}
public void setOnItemClickListener(final OnItemClickListener onItemClickListener) {
this.onItemClickListener = onItemClickListener;
}
#Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View v = LayoutInflater.from(searchContext).inflate(R.layout.ly_search_user, parent,false);
return new ViewHolder(v);
}
#Override
public void onBindViewHolder(final ViewHolder holder, final int position) {
//Set User Name
holder.txtUserName.setText(searchResultsList.get(position).getString("fullName"));
//Set User Location
holder.txtUserLocation.setText(GlobalFunctions.getParseUserLocationAsString(holder.txtUserName.getContext(), searchResultsList.get(position)));
//Set User Profile Image
if (searchResultsList.get(position).getParseFile("profilePicture") != null) {
Glide.with(holder.imgUserProfilePicture.getContext()).applyDefaultRequestOptions(RequestOptions.circleCropTransform()).load(searchResultsList.get(position).getParseFile("profilePicture").getUrl()).into(holder.imgUserProfilePicture);
}
else {
Glide.with(holder.imgUserProfilePicture.getContext()).applyDefaultRequestOptions(RequestOptions.circleCropTransform()).load(R.drawable.ic_profile_place_holder).into(holder.imgUserProfilePicture);
}
//Set Row OnClickListener
holder.rlUserItem.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if (searchResultsList.get(position).getObjectId().equalsIgnoreCase(ParseUser.getCurrentUser().getObjectId())) {
Intent openProfile;
openProfile = new Intent(holder.rlUserItem.getContext(), TimelineActivity.class);
holder.rlUserItem.getContext().startActivity(openProfile);
}
else {
Intent openOtherProfile = new Intent(holder.rlUserItem.getContext(), OtherUserTimelineActivity.class);
openOtherProfile.putExtra("otherUserProfileId", searchResultsList.get(position).getObjectId());
holder.rlUserItem.getContext().startActivity(openOtherProfile);
}
}
});
//Set Friend Action OnClickListener & Image
if (ParseUser.getCurrentUser().getList("friendsArray").contains(searchResultsList.get(position))) {
Glide.with(holder.imgFriendAction.getContext()).load(R.drawable.ic_phone_black_24dp).into(holder.imgFriendAction);
ImageViewCompat.setImageTintList(holder.imgFriendAction, ColorStateList.valueOf(searchContext.getColor(R.color.green)));
}
else if (ParseUser.getCurrentUser().getList("pendingFriendsArray").contains(searchResultsList.get(position))) {
Glide.with(holder.imgFriendAction.getContext()).load(R.drawable.ic_check_black_24dp).into(holder.imgFriendAction);
ImageViewCompat.setImageTintList(holder.imgFriendAction, ColorStateList.valueOf(searchContext.getColor(R.color.gray_dark)));
}
else {
Glide.with(holder.imgFriendAction.getContext()).load(R.drawable.ic_person_add_black_24dp).into(holder.imgFriendAction);
ImageViewCompat.setImageTintList(holder.imgFriendAction, ColorStateList.valueOf(searchContext.getColor(R.color.colorPrimary)));
}
holder.imgFriendAction.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
friendActionListenerAction(holder, searchResultsList.get(position));
}
});
}
private void friendActionListenerAction(ViewHolder holder, ParseUser parseUser) {
if (ParseUser.getCurrentUser().getList("friendsArray").contains(parseUser)) {
FLKCallUtils.showCallDialog(holder.imgFriendAction.getContext());
}
else if (ParseUser.getCurrentUser().getList("pendingFriendsArray").contains(parseUser)) {
//Do nothing
}
else {
//Add Friend
FLKFriendUtils.sendFriendRequestFromUserToUser(ParseUser.getCurrentUser(), parseUser);
//Update Image
Glide.with(holder.imgFriendAction.getContext()).load(R.drawable.ic_check_black_24dp).into(holder.imgFriendAction);
ImageViewCompat.setImageTintList(holder.imgFriendAction, ColorStateList.valueOf(searchContext.getColor(R.color.gray_dark)));
}
}
#Override
public int getItemCount() {
return searchResultsList.size();
}
class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
public MediumRobotoTextView txtUserName;
public RegularRobotoTextView txtUserLocation;
public RelativeLayout rlUserItem;
ImageView imgUserProfilePicture;
ImageView imgFriendAction;
public ViewHolder(View itemView) {
super(itemView);
rlUserItem = (RelativeLayout) itemView.findViewById(R.id.rl_user_container);
rlUserItem.setOnClickListener(this);
txtUserName = (MediumRobotoTextView) itemView.findViewById(R.id.txt_user_name);
txtUserLocation = (RegularRobotoTextView) itemView.findViewById(R.id.txt_user_location);
imgUserProfilePicture = (ImageView) itemView.findViewById(R.id.img_profile_picture);
imgUserProfilePicture.setOnClickListener(this);
imgFriendAction = (ImageView) itemView.findViewById(R.id.img_friend_action);
imgFriendAction.setOnClickListener(this);
}
#Override
public void onClick(View v) {
//TODO - do something here if you wish
}
}

Upon further investigation I found that the parse-android SDK does not fetch pointers the same every single time. For example when I fetch 'friendsArray', let's say right now, it will return
[com.parse.ParseUser#ae66779, com.parse.ParseUser#8371cbe, com.parse.ParseUser#32d511f, com.parse.ParseUser#5fd2c6c, com.parse.ParseUser#7dd0235, com.parse.ParseUser#9c446ca, com.parse.ParseUser#5fe03b]
However if I then fetch it, let's say in 5 minutes, it will return
[com.parse.ParseUser#ec99877, com.parse.ParseUser#674bcg, com.parse.ParseUser#749hhc, com.parse.ParseUser#6fh3d6dg, com.parse.ParseUser#jdj8dk, com.parse.ParseUser#4c966ca, com.parse.ParseUser#3f0eeb]
Additionally, I noted that even the pointer to searchResultsList.get(position) changes it's reference every time I loaded it.
The way I got around this was to create a function (seen below) that returns an array of the actual objectId's of the pointers inside the 'friendsArray'. This way I can guarantee that it will always be returning the same items and can therefore create an accurate 'contains' comparison.
public static List<String> friendsArrayObjectIdsArray() {
//Create Array of Friends
List<ParseUser> friendsArray = ParseUser.getCurrentUser().getList("friendsArray");
//Create Temp Array of Object Id's
List<String> tempObjectIdsArray = new ArrayList<>();
//Iterate List
for (ParseUser friendUser : friendsArray) {
tempObjectIdsArray.add(friendUser.getObjectId());
}
return tempObjectIdsArray;
}
I then run the following comparison to get the result I am looking for
if (FLKUserUtils.friendsArrayObjectIdsArray().contains(searchResultsList.get(position).getObjectId())) {
//Do something
}

Android retrieving data from Firebase doesn't work for data models even it works for other data model in the project with similar codes

I am new in Android and working on an Android app which can retrieve data from firebase. There is a weird problem. I already successfully implemented the retrieving function for one data model of my program, and I used same codes just changed the variables but it doesn't work for another data model. I did many tests and I think the problem is in FirebaseHelper cuz there is no any data returned from the data snapshot. The error is
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
The codes are shown below:
The Activity that shows the retrieved data in a listview.
public class TimeTableActivity extends AppCompatActivity {
DatabaseReference db;
FirebaseHelper firebasehelper;
TimeTableAdapter adapter;
ListView lv_CourseList;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_time_table);
//GET INTENT
Intent intent = this.getIntent();
String majorID = intent.getStringExtra("MAJOR_ID");
lv_CourseList = (ListView) findViewById(R.id.lv_CourseList);
//INITIALIZE FIREBASE DB
db= FirebaseDatabase.getInstance().getReference();
firebasehelper=new FirebaseHelper(db);
//ADAPTER
adapter = new TimeTableAdapter(getApplicationContext(),firebasehelper.retrieveCourse(majorID, new CourseCallbacks() {
#Override
public void onCourseCallback(ArrayList<CourseInfo> courseInfos) {
lv_CourseList.setAdapter(adapter);
}
}));
lv_CourseList.setAdapter(adapter);
}
}
FirebaseHelper:
public class FirebaseHelper{
private DatabaseReference db;
private ArrayList<Major> majors = new ArrayList<>();
private ArrayList<CourseInfo> courseInfos = new ArrayList<>();
public FirebaseHelper(DatabaseReference db) {
this.db = db;
}
//Save the Major info. into db
public Boolean saveMajor(Major major)
{
Boolean saved = null;
if(major==null)
{
saved =false;
}else
{
try
{
db.child("Major").push().setValue(major);
saved =true;
}catch (DatabaseException e)
{
e.printStackTrace();
saved =false;
}
}
return saved;
}
//Save the Course info. into db
public Boolean saveCourse(CourseInfo courseInfo)
{
Boolean saved = null;
if(courseInfo==null)
{
saved =false;
}else
{
try
{
db.child("CourseInfo").push().setValue(courseInfo);
saved =true;
}catch (DatabaseException e)
{
e.printStackTrace();
saved =false;
}
}
return saved;
}
public ArrayList<Major> retrieveMajor(final MajorCallbacks majorCallbacks){
ChildEventListener childEventListener = new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
for (DataSnapshot ds : dataSnapshot.getChildren()) {
Major major = ds.getValue(Major.class);
if (major != null && major.getMajor_id() != null) {
majors.add(major);
}
}
majorCallbacks.onMajorCallback(majors);
}
#Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
for (DataSnapshot ds : dataSnapshot.getChildren()) {
Major major = ds.getValue(Major.class);
if (major != null && major.getMajor_id() != null) {
majors.add(major);
}
}
majorCallbacks.onMajorCallback(majors);
}
#Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
#Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
};
db.addChildEventListener(childEventListener);
if (!majors.isEmpty()){
db.removeEventListener(childEventListener);
}
return majors;
}
public ArrayList<CourseInfo> retrieveCourse(String majorID, final CourseCallbacks courseCallbacks){
ChildEventListener childEventListener = new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String prevChildKey) {
for (DataSnapshot ds : dataSnapshot.getChildren()) {
CourseInfo courseInfo = ds.getValue(CourseInfo.class);
if (courseInfo != null && courseInfo.getCourse_id() != null) {
courseInfos.add(courseInfo);
}
}
courseCallbacks.onCourseCallback(courseInfos);
}
#Override
public void onChildChanged(DataSnapshot dataSnapshot, String prevChildKey) {
for (DataSnapshot ds : dataSnapshot.getChildren()) {
CourseInfo courseInfo = ds.getValue(CourseInfo.class);
if (courseInfo != null && courseInfo.getCourse_id() != null) {
courseInfos.add(courseInfo);
}
}
courseCallbacks.onCourseCallback(courseInfos);
}
#Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
#Override
public void onChildMoved(DataSnapshot dataSnapshot, String prevChildKey) {
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
};
db.child("CourseInfo").orderByChild("major_id").equalTo(majorID).addChildEventListener(childEventListener);
return courseInfos;
}
}
The retrieveMajor method works well even though it returns many null data and repetitive data, and I used the codes of retrieveMajor in retrieveCourse. It doesn't work, the courseInfos is always null. Even though I changed db.child("CourseInfo").orderByChild("major_id").equalTo(majorID).addChildEventListener(childEventListener);
to
db.addChildEventListener(childEventListener);
,still nothing is retrieved which means the problem is not the query (Probably the query is also wrong).
Adapter:
public class TimeTableAdapter extends BaseAdapter {
Context context;
ArrayList<CourseInfo> courseInfos;
public TimeTableAdapter(Context context, ArrayList<CourseInfo> courseInfos) {
this.context = context;
this.courseInfos = courseInfos;
}
#Override
public int getCount() {
return courseInfos.size();
}
#Override
public Object getItem(int pos) {
return courseInfos.get(pos);
}
#Override
public long getItemId(int pos) {
return pos;
}
#Override
public View getView(int position, View convertView, ViewGroup viewGroup) {
LayoutInflater inflater = LayoutInflater.from(context);
if(convertView == null)
{
convertView= LayoutInflater.from(context).inflate(R.layout.model_timetable,viewGroup,false);
}
TextView tv_courseid= (TextView) convertView.findViewById(R.id.tv_courseid);
TextView tv_coursename= (TextView) convertView.findViewById(R.id.tv_coursename);
TextView tv_courseinstructor= (TextView) convertView.findViewById(R.id.tv_courseinstructor);
TextView tv_courseavailable= (TextView) convertView.findViewById(R.id.tv_courseavailable);
final CourseInfo courseInfo= (CourseInfo) this.getItem(position);
tv_courseid.setText(courseInfo.getCourse_id());
tv_coursename.setText(courseInfo.getCourse_name());
tv_courseinstructor.setText(courseInfo.getCourse_instructor());
tv_courseavailable.setText(courseInfo.getCourse_available());
return convertView;
}
}
Data model:
#IgnoreExtraProperties
public class CourseInfo {
public String course_id;
public String course_name;
public int course_section;
public String course_type;
public double course_crdhrs;
public String course_days;
public String course_times;
public String course_location;
public int course_max;
public int course_cur;
public int course_available;
public int course_wl;
public double course_per;
public String course_instructor;
public String course_description;
public String course_prerequire;
public String major_id;
public CourseInfo() {
}
public CourseInfo(String course_id, String course_name, int course_section, String course_type, double course_crdhrs, String course_days, String course_times, String course_location, int course_max, int course_cur, int course_available, int course_wl, double course_per, String course_instructor, String course_description, String course_prerequire, String major_id) {
this.course_id = course_id;
this.course_name = course_name;
this.course_section = course_section;
this.course_type = course_type;
this.course_crdhrs = course_crdhrs;
this.course_days = course_days;
this.course_times = course_times;
this.course_location = course_location;
this.course_max = course_max;
this.course_cur = course_cur;
this.course_available = course_available;
this.course_wl = course_wl;
this.course_per = course_per;
this.course_instructor = course_instructor;
this.course_description = course_description;
this.course_prerequire = course_prerequire;
this.major_id = major_id;
}
public String getCourse_id() {
return course_id;
}
public String getCourse_name() {
return course_name;
}
public int getCourse_section() {
return course_section;
}
public String getCourse_type() {
return course_type;
}
public double getCourse_crdhrs() {
return course_crdhrs;
}
public String getCourse_days() {
return course_days;
}
public String getCourse_times() {
return course_times;
}
public String getCourse_location() {
return course_location;
}
public int getCourse_max() {
return course_max;
}
public int getCourse_cur() {
return course_cur;
}
public int getCourse_available() {
return course_available;
}
public int getCourse_wl() {
return course_wl;
}
public double getCourse_per() {
return course_per;
}
public String getCourse_instructor() {
return course_instructor;
}
public String getCourse_description() {
return course_description;
}
public String getCourse_prerequire() {
return course_prerequire;
}
public String getMajor_id() {
return major_id;
}
}
If you need more codes or information, please comment and let me know. I will really appreciate if you can also help me solve the null data and repetitive data problem cuz it makes the listview show many blank and repetitive items.

You cannot return something now that hasn't been loaded yet. With other words, you cannot just simply create a method that as a return type, an ArrayList<Major> and in the same time return that object. This is happening because those methods, onChildAdded(), onChildChanged() and so on, have an asynchronous behaviour, which means that are called even before you are getting/updating the data from/in the database. To solve this, you can move the declaration of that ArrayList inside one method and do what you need to do with it or dive into asynchronous world and use the last part of my answer from this post. You can take also a look at this video for a better understanding.