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How to read data from Firebase Database? - Java

I'm making a game, if the player wins, then the victory is added to the database. How can I read the data from here?
and paste here:
I read the player's name in a different way, which cannot be repeated with victories and defeats.

To be able to read the data under the jjjj node, please use the following lines of code:
DatabaseReference db = FirebaseDatabase.getInstance().getReference();
DatabaseReference nameRef = db.child("players").child("jjjj");
nameRef.get().addOnCompleteListener(new OnCompleteListener<DataSnapshot>() {
#Override
public void onComplete(#NonNull Task<DataSnapshot> task) {
if (task.isSuccessful()) {
DataSnapshot snapshot = task.getResult();
String loses = snapshot.child("loses").getValue(Long.class);
String name = snapshot.child("name").getValue(String.class);
String wins = snapshot.child("wins").getValue(Long.class);
Log.d("TAG", loses + "/" + name + "/" + wins);
} else {
Log.d("TAG", task.getException().getMessage()); //Never ignore potential errors!
}
}
});
The result in the logcat will be:
3/jjjj/4
Things to notice:
Always create a reference that points to the node that you want to read.
If your database is located in another lcoation than the default, check this answer out.

use this method
This is the method of fetching data from the firebase realtime database
DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
reference.child("players").child(name).addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot snapshot) {
for (DataSnapshot dataSnapshot : snapshot.getChildren()){
}
}
#Override
public void onCancelled(#NonNull DatabaseError error) {
}
});

Firebase Datasnapshot returns null value

I want to retrieve this value from this node ("id"), and the value i get is null. I have googled so many solutions that this might have to do with asynchronous way or something, i guess?
This is the database, and the highlighted node is the value i would like to get:
This is my code:
reference = FirebaseDatabase.getInstance().getReference();
id = null;
Query lastQuery = reference.child("Donation Request").orderByKey().limitToLast(1);
lastQuery.addListenerForSingleValueEvent(new ValueEventListener()
{
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot)
{
if (dataSnapshot.child("id").exists())
{
id = dataSnapshot.child("id").getValue().toString();
int index = Integer.parseInt(id) + 1;
id = Integer.toString(index);
Toast.makeText(getApplicationContext(), "It works!!!", Toast.LENGTH_SHORT).show();
}
else
{
id = "1";
Toast.makeText(getApplicationContext(), "It doesn't work.", Toast.LENGTH_SHORT).show();
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError)
{
}
});
Most appreciated if someone can help me out of this!

When you execute a query against the Firebase Database, there will potentially be multiple results. So the snapshot contains a list of those results. Even if there is only a single result, the snapshot will contain a list of one result.
Your onDataChange needs to handle this list by looping over dataSnapshot.getChildren()):
reference = FirebaseDatabase.getInstance().getReference();
id = null;
Query lastQuery = reference.child("Donation Request").orderByKey().limitToLast(1);
lastQuery.addListenerForSingleValueEvent(new ValueEventListener()
{
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot)
{
for (DataSnapshot snapshot: dataSnapshot.getChildren()) {
if (snapshot.hasChild("id"))
{
id = snapshot.child("id").getValue(String.class);
int index = Integer.parseInt(id) + 1;
id = Integer.toString(index);
Toast.makeText(getApplicationContext(), "It works!!!", Toast.LENGTH_SHORT).show();
}
else
{
id = "1";
Toast.makeText(getApplicationContext(), "It doesn't work.", Toast.LENGTH_SHORT).show();
}
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError)
{
throw databaseError.toException(); // never ignore errors.
}
});
A few more notes:
Any use of id needs to happen inside onDataChange, or be called from there. Outside of that, you won't have any guarantees that id will have been assigned the value you expect.
Using toasts for debugging is bound to become confusing. I highly recommend using Log.d(...) and friends, and studying the output (and its order) in the logcat output of your app.

How to check for a specific value exist in the firebase realtime database?

I am trying to write a query to check if there is any "Pending" status on mcustDeliveryStatus. I want to check in Order node that is there any Pending status for mcustDeliveryStatus.
I wrote the following query
mDatabase = FirebaseDatabase.getInstance().getReference("Order");
final Query query = mDatabase.OrderByChild("mcustDeliveryStatus").equalTo("Pending");
query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
Toast.makeText(VWelcome.this, "new order", Toast.LENGTH_LONG).show();
Intent i = new Intent(VWelcome.this, ViewOrderRequest.class);
startActivity(i);
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
This query works fine but the problem is intent runs even when there is no Pending status in my Order node. Anyone knows why?

Since you annotate your DataSnapshot object with #NonNull, it means that you tell the compiler that your object cannot be null, so it will always return something. With other words, if there are no results, it will return an empty DataSnapshot object. To solve this, you should check how many children are inside that object using the following lines of code:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference orderRef = rootRef.child("Order");
Query query = orderRef.orderByChild("mcustDeliveryStatus").equalTo("Pending");
ValueEventListener valueEventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
long count = dataSnapshot.getChildrenCount();
if (count > 0) {
for(DataSnapshot ds : dataSnapshot.getChildren()) {
String mGasBand = ds.child("mGasBand").getValue(String.class);
Log.d(TAG, mGasBand);
}
} else {
Log.d(TAG, "No data!");
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
Log.d(TAG, databaseError.getMessage()); //Don't ignore errors!
}
};
query.addListenerForSingleValueEvent(valueEventListener);

SingleValueEventListener do not get the value after button click

I need to get nickname value from Firebase Real time database after button is clicked. So i made singleValueListner() in button´s onClick method. But it don´t work.
I have tried debug it, but code didn´t get into singleValueEventListener()
Button getName = (Button)findViewById(R.id.getName);
getName.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
DatabaseReference db = FirebaseDatabase.getInstance().getReference().child("Member").child(user.getUid());
db.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot data : dataSnapshot.getChildren()) {
TextView tv = (TextView)findViewById(R.id.tv);
tv.setText(data.child("nickname").getValue().toString());
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
});
Database JSON structure:
{
"Member" : {
"1Zuv6VZZ0kPluwc33f1QQQ7DZD93" /* UID */ : {
"-LgIHwiAjfuh5pjK7wzl" : {
"actualScore" : 0,
"bestScore" : 0,
"email" : "some#email.com",
"nickname" : "Vitek",
"season" : 0
}
}
}
}
Database structure:
https://drive.google.com/file/d/15B4b6Rb_WAiS6fioI9gItyijrbDiVjzJ/view
I need to get nickname, I think this is writen good, but not. So, what is wrong?

To get the value of your nickname property, please use the following lines of code:
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference uidRef = rootRef.child("Member").child(uid);
ValueEventListener valueEventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
String nickname = dataSnapshot.child("nickname").getValue(String.class);
Log.d(TAG, nickname);
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
Log.d(TAG, databaseError.getMessage()); //Don't ignore errors!
}
};
uidRef.addListenerForSingleValueEvent(valueEventListener);
The output in your logcat will be:
Vitek
So there is no need to loop through the DataSnapshot object in order to get the value of your nickname property. If you don't get this result, please check the logcat to see if you have an error message printed out.

You are only referring up to user's id but there is also a parent key of user detail which you need to reference.
tv.setText(data.child("LgiH------").child("nickname").getValue().toString());
but try to remove that second key from your registering user's code because it is not helpful.

You have made a mistake in refering your firebase root node. just change your line as below :
DatabaseReference db = FirebaseDatabase.getInstance().getReference("Member");
Now,just call your singlevalue event.
db.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot data : dataSnapshot.getChildren()) {
TextView tv = (TextView)findViewById(R.id.tv);
tv.setText(data.child("nickname").getValue().toString());
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
This will do your stuff. try debugging your code with log at step by step.

how to get string array from firebase realtime database

databaseReference = FirebaseDatabase.getInstance().getReference("/sample");
databaseReference.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
Log.d(TAG, "onDataChange: dataSnapshot "+dataSnapshot.getValue());
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
I'm new to android app development and firebase as well. i m fetching data from sample node and getting DataSnapshot value like below.
{size=[Small, Large, Ex-Large], type=[Type 1, Type 2], color=[Red, Green, Blue], category=[T-Shirt, Jeans, Sweater]}
need some expect help, any suggestion will greatly appreciated.
Thanks

To retrieve values separately, you can use a code like this:
databaseReference.child("category").addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (int i=0;i<3;i++) {
// category is an ArrayList you can declare above
category.add(dataSnapshot.child(String.valueOf(i)).getValue(String.class));
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) { // Do something for this
}
});
Similarly you can add values of other nodes in your other ArrayLists, just by changing the value of Childs in this code.

Firebase has no native support for arrays. If you store an array, it really gets stored as an "object" with integers as the key names.
// we send this
['hello', 'world']
// Firebase stores this
{0: 'hello', 1: 'world'}
Best Practices: Arrays in Firebase
// TRY THIS
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
youNameArray = new ArrayList<>();
for (DataSnapshot snapshot : dataSnapshot.getChildren()){
String data = snapshot.getValue(String.class);
youNameArray.add(data);
}
Log.v("asdf", "First data : " + youNameArray.get(0));
}

Something like this:
databaseReference = FirebaseDatabase.getInstance().getReference("/sample");
databaseReference.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot sampleSnapshot: dataSnapshot.getChildren()) {
Log.d(TAG, "onDataChange: sampleSnapshot "+sampleSnapshot.getKey()+" = "+sampleSnapshot.getValue());
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
throw databaseError.toException(); // don't ignore errors
}
});
The difference is that in my answer I loop over dataSnapshot.getChildren() to get each individual sample snapshot. The sampleSnapshot.getValue() call should return a List.

FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference refence = database.getReference();
refence.addValueEventListener(new ValueEventListener()
{
#Override
public void onDataChange(DataSnapshot snapshot) {
// TODO Auto-generated method stub
ArrayList array= new ArrayList<>();
for (DataSnapshot ds : snapshot.getChildren()){
String data = ds.getValue().toString();
array.add(data);
}
System.out.println(array);
}
#Override
public void onCancelled(DatabaseError error) {
// TODO Auto-generated method stub
}
});
In my case String.class does not work instead .toString method works
String data = ds.getValue().toString();