Develop Reference

How to set activity layout based on user type / role?

I am working on an Android app with 2 types of users (doctors and patients), and I want each type to have their own UI. For eg, doctors must see ' Add days off' and patients must see ' Book appointment' . Somehow I don't get anywhere with whatever I try.
I also use Firebase Auth and Realtime Database which makes the user type retrieval kinda tricky. So far I've tried a lot of Async classes, methods, variables, shared preferences, retrieving data while on launcher splash screen.
The best I got is getting the user to login, it shows the good layout, then I start the app again and it shows the wrong layout. Somehow I noticed it just works on the second run, but not always so the behaviour is unpredictable to me at least. But at least the user type from the database is retrieved.
I have a class that extends Application, which checks if there's an user authenticated and then redirects the user to either LoginActivity, or MainMenuActivity.
I have created a method that retrieves the Firebase Auth user data from Realtime Database, looping through both Doctors and Patients 'children' until it finds the current user email and gets its type. Since Realtime Database is asynchronous, the methos gets an interface as an argument, and after the loop, the I call the interface's method, which sets a static boolean variable (isUserDoctor).
Before setting the content view (with 2 possible layouts), I call the function described before and it works the way I first mentioned, which is not good.
The method that retrives data
public void getUserType(final DataStatus dataStatus) {
currentUser = FirebaseAuth.getInstance().getCurrentUser();
currentUserEmail = currentUser.getEmail();
databaseReference = FirebaseDatabase.getInstance().getReference("Users");
databaseReference.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
currentUserType.clear();
FirebaseManager.isUserDoctor = false;
DataSnapshot allDoctors = dataSnapshot.child("Doctors");
DataSnapshot allPatients = dataSnapshot.child("Patients");
for (DataSnapshot ds : allDoctors.getChildren()) {
if (currentUserEmail.equals(Utils.decodeUserEmail(ds.getKey()))) {
currentUserType.add(ds.child("userType").getValue().toString());
} else {
for (DataSnapshot dsPacient : allPatients.getChildren()) {
if (currentUserEmail.equals(Utils.decodeUserEmail(dsPacient.getKey()))) {
currentUserType.add(dsPacient.child("userType").getValue().toString());
}
}
}
}
dataStatus.DataIsLoaded(currentUserType.get(0).toString());
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
The interface
public interface DataStatus {
void DataIsLoaded(String userType);
}
The method's call in Main Menu
FirebaseManager.getInstance().getUserType(new DataStatus() {
#Override
public void DataIsLoaded(String userType) {
if ("doctor".equals(userType))
FirebaseManager.isUserDoctor = true;
else
FirebaseManager.isUserDoctor = false;
}
});
if (FirebaseManager.isUserDoctor)
setContentView(R.layout.activity_main_menu_doctor);
else
setContentView(R.layout.activity_main_menu);
So if anyone has any ideas about how to show the proper layout and allow functions based on user role/type please share. What I basically need is to retrieve the userType from the current email just in time to set a variable needed throughout the whole app in order to hide/show certain views.

How to fix a List<> that become null inside OnCreateView()

I am trying to retrieve data from Firebase realtime-database and put it on a CardView inside a RecyclerView inside a Fragment.
But the Fragment shown is blank white with no error. I retrieve the data inside OnCreate method and add it into a List.
While debugging the application, found out that even after assigning the retrieved data inside the onCreate method, the list is still NULL inside the onCreateView method.
Fragment Dashboard List Class:
public class fragment_dashboard_list extends Fragment {
List<ibu> ibu_ibu;
FirebaseDatabase database;
DatabaseReference myRef ;
String a;
public fragment_dashboard_list() {}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ibu_ibu = new ArrayList<>();
database = FirebaseDatabase.getInstance();
myRef = database.getReference("Guardian");
myRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
// This method is called once with the initial value and again
// whenever data at this location is updated.
for(DataSnapshot dataSnapshot1 : dataSnapshot.getChildren()){
ibu value = dataSnapshot1.getValue(ibu.class);
ibu ibu_val = new ibu();
String alamat = value.getAlamat();
String foto = value.getFoto();
String hp = value.getHp();
String ktp = value.getKtp();
String nama = value.getNama();
String privilege = value.getPrivilege();
String ttl = value.getTtl();
ibu_val.setAlamat(alamat);
ibu_val.setFoto(foto);
ibu_val.setHp(hp);
ibu_val.setKtp(ktp);
ibu_val.setNama(nama);
ibu_val.setPrivilege(privilege);
ibu_val.setTtl(ttl);
// Here the List ibu_ibu is not NULL
ibu_ibu.add(ibu_val);
}
}
#Override
public void onCancelled(DatabaseError error) {
// Failed to read value
Log.w("Hello", "Failed to read value.", error.toException());
}
});
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_dashboard_list, container, false);
RecyclerView myrv = (RecyclerView) view.findViewById(R.id.dashboard_recycler_view);
//Here the List ibu_ibu is null
adapter_list_ibu myAdapter = new adapter_list_ibu(ibu_ibu);
LinearLayoutManager LinearLayoutManager = new LinearLayoutManager(getContext());
myrv.setLayoutManager(LinearLayoutManager);
myrv.setAdapter(myAdapter);
return view;
}
}
I expected the List to be not NULL inside OnCreateView so the Fragment wont Blank

Firebase APIs are asynchronous, which means that onDataChange() method returns immediately after it's invoked, and the callback will be called some time later. There are no guarantees about how long it will take. So it may take from a few hundred milliseconds to a few seconds before that data is available.
Because that method returns immediately, your ibu_val list that you're trying to use it outside the onDataChange() method, will not have been populated from the callback yet and that's why is always empty.
Basically, you're trying to use a value of variable synchronously from an API that's asynchronous. That's not a good idea, you should handle the APIs asynchronously as intended.
A quick solve for this problem would be to notify the adapter once you got all elements from the database using:
myrv.notifyDatasetChanged();
So add this line of code right after where the for loop ends.
If you intent to use that list outside the callback, I recommend you see the last part of my anwser from this post in which I have explained how it can be done using a custom callback. You can also take a look at this video for a better understanding.

Android Firebase - Reading data from firebase prior to inflating layout

I'm trying to get a user's profile from a Firebase DB. Then using the user's information I want to set TextViews in my Fragment's layout to reflect the user's individual stats.
The problem is that the rootViw is being returned prior to having recieved the user's profile. And so I get a null object reference error.
My understanding of the fragment's life cycle is that onCreate() is created first and so I tried placing the DB code there but I get the same problem. I then figured that if accessing the DB is slower than my onCreateView() I'll place a Thread.sleep() timer to wait for the DB call to complete and then perform the rest of my code. Which I know is a stupid solution but just wanted to test my theory; that also failed so obviously my understanding is wrong.
Where should I place my DB call so that it completes prior to returning my rootView? Why does placing the DB listener in OnCreate() not work and why does the Thread.sleep() delay not work?
Leaderboard Fragment
public class Leaderboard extends Fragment{
private FirebaseAuth mFirebaseAuth;
private DatabaseReference mUserDatabaseReference;
private User user;
private TextView scoreView;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_leaderboard,
container, false);
scoreView = rootView.findViewById(R.id.leaderboard_score);
mFirebaseAuth = FirebaseAuth.getInstance();
final String userUID = mFirebaseAuth.getCurrentUser().getUid();
mUserDatabaseReference =
FirebaseDatabase.getInstance().getReference("users");
mUserDatabaseReference.addListenerForSingleValueEvent(new
ValueEventListener() {
#Override
public void onDataChange(DataSnapshot snapshot) {
if (snapshot.hasChildren()) {
for (DataSnapshot messageSnap: snapshot.getChildren()) {
if(messageSnapshot.getKey().equals(userUID)) {
user = messageSnapshot.getValue(User.class);
}}}}
#Override
public void onCancelled(DatabaseError databaseError) {}
});
//Causes error because user==null
scoreView.setText("Score: " + user.getScore());
return rootView;
}
}

All Firebase APIs are asynchronous. You should expect that listeners may be called after any amount of time, based on the quality of the hardware and its network connection. Don't ever use Thread.sleep() to try to control the timing of things - that is an anti-pattern.
My suggestion to you is to inflate a "loading" screen in onCreateView() to display immediately, so the user doesn't have to look at a blank screen when your fragment starts. Then, when your listener is called with the data you want to display, add or update other views as needed.

Why not set the score after you get the DB result ?
mUserDatabaseReference.addListenerForSingleValueEvent(new
ValueEventListener() {
#Override
public void onDataChange(DataSnapshot snapshot) {
if (snapshot.hasChildren()) {
for (DataSnapshot messageSnap: snapshot.getChildren()) {
if(messageSnapshot.getKey().equals(userUID)) {
user = messageSnapshot.getValue(User.class);
}
}
scoreView.setText("Score: " + user.getScore());
}}
#Override
public void onCancelled(DatabaseError databaseError) {}
});

Get the data from the Firebase in limit to perform pull to refresh and load more functionality

Yet now i am getting the all data from the FireBase at one time.What i want to do that getting data in LIMITS like 15 records at a time. Like in first time user get the 15 records from the Firebase and when user load more data at the bottom/TOP of the screen than 15 more records should come from Firebase and added to the bottom/TOP of the list.
I have implemented the logic to get the 15 records at a top OR bottom of the database from Firebase like below:-
public class ChatActivity extends AppCompatActivity implements FirebaseAuth.AuthStateListener {
private FirebaseAuth mAuth;
private DatabaseReference mChatRef;
private Query postQuery;
private String newestPostId;
private String oldestPostId;
private int startAt = 0;
private SwipeRefreshLayout swipeRefreshLayout;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_chat);
mAuth = FirebaseAuth.getInstance();
mAuth.addAuthStateListener(this);
mChatRef = FirebaseDatabase.getInstance().getReference();
mChatRef = mChatRef.child("chats");
/////GETTING THE VIEW ID OF SWIPE LAYOUT
swipeRefreshLayout = (SwipeRefreshLayout) findViewById(R.id.swipeRefreshLayout);
/////GETTING FIRST 10 RECORDS FROM THE FIREBASE HERE
mChatRef.limitToFirst(10).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot child : dataSnapshot.getChildren()) {
oldestPostId = child.getKey();
System.out.println("here si the data==>>" + child.getKey());
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
//////FOR THE PULL TO REFRESH CODE IS HERE
swipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
#Override
public void onRefresh() {
// Refresh items
System.out.println("Here==>>> "+oldestPostId);
///HERE "oldestPostId" IS THE KEY WHICH I GET THE LAST RECORDS FROM THE FIREBASE
mChatRef.startAt(oldestPostId).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot child : dataSnapshot.getChildren()) {
System.out.println("here AFTER data added==>>" + child.getKey());
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
});
}
I have searched here on SO for it , but did not get the expected result, below link which i have searched for it
1. First Link
2. Second Link
3. Third Link
4. Forth Link
Please look at my firebase data structure in image.
I have implemented the logic for the getting 15 OR 10 records at first time and it works..and also implemented the logic for loading more records in limits but not getting proper solution (NOT WORKING) , please help and let me know where am i doing wrong..Thanks :)
EDIT SOLUTION
:- I have implemented the load more or pull to refresh functionality on this link:- Firebase infinite scroll list view Load 10 items on Scrolling

You are missing orderByKey(). For any filtering queries you must use the ordering functions. Refer to the documentation
In your onRefresh method you need to set the limit:
public void onRefresh() {
// Refresh items
///HERE "oldestPostId" IS THE KEY WHICH I GET THE LAST RECORDS FROM THE FIREBASE
mChatRef.orderByKey().startAt(oldestPostId).limitToFirst(10).addListenerForSingleValueEvent(new ValueEventListener() {
.....
So the data you retrieve is the only 10 new records after you got your first 10 records.
Make sure to save the oldest key of the newly retrieved data so that on next refresh new data from this key is only retrieved.
Suggestion: Instead of adding a child value listener to find the last key, you can just use the value listener and get the last data snapshot with the size to get the last record's key.

restructure your database, set a new child id which is incremental like 0,1,2,3... etc
"chats": {
"-KZLKDF": {
"id": 0,
"message": "Hi",
"name":"username"
},
then make a method for query
public void loadFromFirebase(int startValue,int endValue){
mChatRef.orderByChild(id).startAt(startValue).endAt(endValue).addListenerForSingleValueEvent(this);
}
make sure you have implemented addListenerForSingleValueEvent then do adapter related task.
Initially call from onCreate method:
loadFromFirebase(0,10);
NB: loading new content in the list you have to be aware with adapter.

Saving data from Firebase into a list

I'm currently developing an Android app that deals with storing book translations. I'm using Firebase to hold all the data online, and I have no trouble pulling data from it and storing them as Book objects. I have a master list of books in the main class that stores all the books from the Firebase database, however the list doesn't seem to update properly.
public static List<Book> books = new ArrayList<Book>();
protected void onCreate(Bundle savedInstanceState) {
myFirebaseRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot snapshot) {
for (DataSnapshot bookSnapshhot : snapshot.getChildren()) {
Book book = bookSnapshhot.getValue(Book.class);
books.add(book);
System.out.println(book.getAuthor() + " - " + book.getTitle());
for (Chapter chapter : book.getChapters()) {
System.out.println(chapter.getTitle());
}
for (Genre genre : book.getGenres()) {
System.out.println(genre.getGenre());
}
System.out.println(books.size());
}
}
#Override public void onCancelled(FirebaseError error) { }
});
System.out.println(books.size());
}
In that body, the size of books is correct (right now it is only 1). However if I call the same print statement outside of that code body (the last line), it gives me 0. I don't know why, because it successfully adds it inside the onDataChange() method but it seems to not apply the changes on the outside.

I think that your problem is about the asyncronously of the ValueEventListener.
The onDataChange is called asynconously.
You have to use the books after the onDataChange is called.

The addValueEventListener() will fetch the data from Firebase asynchronously.
What your code depicts is that you are adding ValueEventListener and then printing System.out.println(books.size());. This means your logs gets displayed after you add ValueEventListener(which doesn't means your listener gets invoked). At this point your listener is not invoked yet and so isn't onDataChange(). Thus you won't ever get updated count outside the listener scope.