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Get data from firebase Realtime database

I want to get data from firebase in sorted manner, I tried below method but its not working propely and collects all the data.
Here is the image for my firebase database :
DatabaseReference databaseRef = FirebaseDatabase.getInstance().getReference();
String input = "G";
Date cd = Calendar.getInstance().getTime();
SimpleDateFormat df = new SimpleDateFormat("dd-MMM-yyyy", Locale.getDefault());
String formattedDate = df.format(cd);
FirebaseUser currentUser = mAuth.getCurrentUser();
DatabaseReference data = databaseRef.child("Data").child(currentUser.getUid()).child(formattedDate.toString()).child(medname.toString());
databaseRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot snapshot) {
List<String> data = new ArrayList<String>();
for (DataSnapshot postSnapshot : snapshot.getChildren()) {
data.add(postSnapshot.getValue().toString());
}
Log.d("datafriebase",""+data);
}
I want to get data in sorted manner, like value of 1, value of 2 but i am getting whole database

You're getting the whole database, because you're reading from databaseRef, which you initialized as:
DatabaseReference databaseRef = FirebaseDatabase.getInstance().getReference();
To get only the nested data, read from data, which you set to reference that path:
DatabaseReference data = databaseRef.child("Data").child(currentUser.getUid()).child(formattedDate.toString()).child(medname.toString());
So:
data.addValueEventListener(new ValueEventListener() {
...

How to get the key of a pushed value

In Firebase Realtime Database on Android, I want to retrieve this id "-Mb1sSv-FCNr9ElxZIwN".
databaseReference = FirebaseDatabase.getInstance().getReference().child("Registration Data1");
mDBListener = databaseReference.orderByKey().limitToLast(1).addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
mTeachers.clear();
for (DataSnapshot teacherSnapshot : dataSnapshot.getChildren()) {
Data DB = teacherSnapshot.getValue(Data.class);
DB.setKey(teacherSnapshot.getKey());
mTeachers.add(DB);
}
mAdapter.notifyDataSetChanged();
mProgressBar.setVisibility(View.GONE);
}

It looks to me that KAsr ... dhz1 is the user ID that comes from the authentication process. If so, that UID should also be added to your reference. So to be able to get this id "-Mb1sSv-FCNr9ElxZIwN", please change the following reference:
databaseReference = FirebaseDatabase.getInstance().getReference().child("Registration Data1");
To:
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
databaseReference = FirebaseDatabase.getInstance().getReference().child("Registration Data1").child(uid);
Meaning that:
DB.setKey(teacherSnapshot.getKey());
Will set the above key to the "DB" object.

Why does my firebase database child return null?

I am working with firebase database and i was trying to get the value of a child using this code below and may System.out.println(MyCredit.toString()); is always returns null: Please see my firebase database
DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("Users");
ref.addListenerForSingleValueEvent(
new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
//Get map of users in datasnapshot
CollectCredits((Map<String,Object>) dataSnapshot.getValue());
}
#Override
public void onCancelled(DatabaseError databaseError) {
//handle databaseError
}
});
private void CollectCredits(Map<String,Object> users) {
MyCredit = new ArrayList<>();
//iterate through each user, ignoring their UID
for (Map.Entry<String, Object> entry : users.entrySet()){
//Get user map
Map singleUser = (Map) entry.getValue();
//Get Credit field and append to list
MyCredit.add((Long) singleUser.get("Credit"));
Toast.makeText(MainActivityCustonlistViewnew.this, "Credit : " +String.valueOf(MyCredit), Toast.LENGTH_SHORT).show();
}
System.out.println(MyCredit.toString());
}

Try this:
private void CollectCredits(DataSnapshot dataSnapshot) {
MyCredit = new ArrayList<>();
//iterate through each dataSnapshot
for (DataSnapshot d1 : dataSnapshot.getChildren()){
MyCredit.add(d1.getValue());
}
}

Let me give you some suggestions, Try to check your firebase database path both the root and child path because some time you did everything correctly but the path you specified to your Database reference which is not referring to the correct path. So it can produce the same result what are getting right now.

Filter results by an Edit Text

In my ExploreFragment.java I have an EditText which basically allows the user to search country names that are stored in my Firebase Realtime Database.
What I want to achieve is, when the user types something in the EditText and then presses "submit" in their keyboard, it makes a query that retrieves every country which has the string they typed in their name, and get redirected to my fragment FilteredResultsFragment.java which displays the names of the countries retrieved. My fragment has a recycler view with an Adapter.
I haven't achieved this yet. I need to retrieve a List with the urls and a List with the names.
The query should look like this:
FirebaseDatabase mDatabase = FirebaseDatabase.getInstance();
Log.d("TAMANHO","size = "+paisEscolhido.size());
for (int i = 0; i<paisEscolhido.size(); i++) {
Log.d("CONTINETNE","size = "+paisEscolhido.get(i));
DatabaseReference paisNomeContinentes = mDatabase.getReference().child("paises");
Query queries = paisNomeContinentes.orderByChild("Continente").equalTo(paisEscolhido.get(i));
queries.addListenerForSingleValueEvent(new com.google.firebase.database.ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
List<String> imagemPaisList = new ArrayList<>();
List<String> nomePaisList = new ArrayList<>();
for (DataSnapshot ds : dataSnapshot.getChildren()) {
String imagemPais = ds.child("Imagem").getValue(String.class);
String nomePais = ds.child("Nome").getValue(String.class);
imagemPaisList.add(imagemPais);
nomePaisList.add(nomePais);
}
int urlCount = imagemPaisList.size();
// int randomImage = new Random().nextInt(urlCount);
for (int i = 0; i < nomePaisList.size(); i++) {
Integer randomVariavel = new Random().nextInt(urlCount);
randomImagemPaisList.add(imagemPaisList.get(randomVariavel));
randomNomePaisList.add(nomePaisList.get(randomVariavel));
}
UPDATE
I've come up with this query:
FirebaseDatabase mDatabase = FirebaseDatabase.getInstance();
DatabaseReference paisNomeContinentes = mDatabase.getReference().child("paises");
Query queries = paisNomeContinentes.orderByChild("Nome").startAt("Po");
queries.addListenerForSingleValueEvent(new com.google.firebase.database.ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
List<String> imagemPaisList = new ArrayList<>();
List<String> nomePaisList = new ArrayList<>();
for (DataSnapshot ds : dataSnapshot.getChildren()) {
String imagemPais = ds.child("Imagem").getValue(String.class);
String nomePais = ds.child("Nome").getValue(String.class);
imagemPaisList.add(imagemPais);
nomePaisList.add(nomePais);
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
That should retrieve the Name of the country that starts with the value the user writes in my EditText but, when I write, for example "Po", it should give me "Portugal" and "Poland" but, instead, it gives me random images...
This is the data structure:
UPDATE V2
It actually gives me "Poland" and "Portugal" as the top results but it shows my more ImageView besides those two (and with random images too)...

If you want to use startAt() to filter your data you also have to use endAt() because startAt() works as a starting point for your query and not a filter. By adding \uf8ff (the last unicode character) behind your searchstring in endAt() you limit your query to get only the values that start with your searchstring:
Query queries = paisNomeContinentes.orderByChild("Nome").startAt("Po").endAt("Po" + "\uf8ff");
Just remember this will only get the items that start with the searchstring, not the items that contain the searchstring.

firebase how to get child of child?

so i am stuck. i want to retrieve child of child from my firebase database.
my database struture looks like this
users{
user1{
name:
regno:
carmodel:
caryear}
user2{
name:
regno:
carmodel:
caryear}
user3{
name:
regno:
carmodel:
caryear}}
Regno = car registration number.
when i type in a "carreg no" and press ok. i want the code to search every carreg. if a match is found execute next set of codes.
so far i have tried to store it in a array. but the code seems to fail when i put reg or any variable name that exist.
public void input(){
FirebaseDatabase firebase = FirebaseDatabase.getInstance();
final DatabaseReference table_user = firebase.getReference("User");
table_user.addListenerForSingleValueEvent(
new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
//Get map of users in datasnapshot
collectPhoneNumbers((Map<String,Object>) dataSnapshot.getValue());
}
#Override
public void onCancelled(DatabaseError databaseError) {
//handle databaseError
}
});
private void collectPhoneNumbers(Map<String,Object> users) {
ArrayList<Long> phoneNumbers = new ArrayList<>();
//iterate through each user, ignoring their UID
for (Map.Entry<String, Object> entry : users.entrySet()){
//Get user map
Map singleUser = (Map) entry.getValue();
//Get phone field and append to list
phoneNumbers.add((Long) singleUser.get("namesd"));
}
System.out.println(phoneNumbers.toString());
mVoiceInputTv.setText("" + phoneNumbers);
}
}
i got this from another stackflow. before this i tried creating a for look. it was successfull but result failed 80% of the time. (not always correct).

To solve this, you need to query your database using orderByChild() method like this:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference usersRef = rootRef.child("users");
Query regnoQuery = usersRef.orderByChild("regno").equalsTo(regno);
In which regno argument from equalsTo() is the the actual registration number that you are looking for. Then attach a listener to the regnoQuery and use getChildrenCount() method on the dataSnapshot object. If the number of childrens is noOfChildrens > 0 then execute the set of codes you need.

private FirebaseDatabase mdatabase;
private DatabaseReference mdatabaseRef;
mdatabase = FirebaseDatabase.getInstance();
mdatabaseRef = mdatabase.getReference();
mdatabaseRef.child("users").child("users1").orderByChild("regno").equalsTo(regno).addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot childSnapshot : dataSnapshot.getChildren()) {
}
}