Develop Reference

Firebase Database Read Data

I am trying to read some values from Firebase Real time database.
My structure looks like this:
and my code to retrieve the value("Wine and Dine"):
databaseReference.child("test").child("event_name").child("drinks")
.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
Object dataSnapshotObject = dataSnapshot.getValue(String.class);
if(dataSnapshotObject != null){
Toast.makeText(content, "Event Name: " + dataSnapshotObject.toString(), Toast.LENGTH_LONG).show();
}else
Toast.makeText(context,"null",Toast.LENGTH_SHORT).show();
}
#Override
public void onCancelled(DatabaseError databaseError) {
});
However, I only get a null response as the value. What could I be doing wrong?

You may remove .child("drinks") from the chain (and put it in later, as in code below)and if you want to make the dataSnapshotObject to String anyway, then you should retrieve it in a String.
Something like this:
String value = dataSnapshot.child("drinks").getValue(String.class);
Also check if your databaseReference looks something like this or not.
DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference();

You can use addListenerForSingleValueEvent to get the value
Code sample:
FirebaseDatabase.getInstance().getReference().child("test").child("event_name").addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
HashMap hashUser = (HashMap) dataSnapshot.getValue();
if (hashUser != null) {
String Drinks = hashUser.get("drinks").toString();
//Toast.makeText(this, Drinks , Toast.LENGTH_SHORT).show();
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});

How to retrieve parent key in firebase android

I want to retrieve houfxWvbwyVmbHX60IGjpNkZR9w2 key , How to do?
Here is the code for the same
mQuery = mfollowing.orderByChild("following").equalTo(user_id);
mQuery.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
final String key = dataSnapshot.getKey();
mdatabaseUsers.child(user_id).addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
DatabaseReference newfollscreen = mdatabaseFollwer.child(key).child(newPost.getKey());
newfollscreen.child("screen").setValue(downloadUrl.toString());
newfollscreen.child("engagement").setValue("NA");
newfollscreen.child("url").setValue("NA");
newfollscreen.child("uid").setValue(user_id);
newfollscreen.child("name").setValue(dataSnapshot.child("name").getValue());
newfollscreen.child("image").setValue(dataSnapshot.child("image").getValue()).addOnCompleteListener(new OnCompleteListener<Void>() {
#Override
public void onComplete(#NonNull Task<Void> task) {
if (task.isSuccessful()){
Toast.makeText(AddimageActivity.this, "Posted among your followers", Toast.LENGTH_SHORT).show();
}else {
Toast.makeText(AddimageActivity.this, "Error", Toast.LENGTH_SHORT).show();
}
}
});
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
#Override
public void onCancelled (DatabaseError
databaseError){
}
});
Here is the Firebase database
second image
enter image description here
I tried using child data snapshot method but did not worked. Any help for this will be much appreciated.

Assuming you have a DataSnapshot that points to the children rhZ4...wt2, you can call snapsthot.getRef().toString() which will return you something like https://xxx.firebaseio.com/.../houfxWvbwyVmbHX60IGjpNkZR9w2/rhZ4...wt2. From there you can extract the parent key.
From your example, after you query the database using mQuery, inside onDataChange you have a DataSnapshot.
So calling dataSnapshot.getRef().toString() will give you https://xxx.firebaseio.com/.../houfxWvbwyVmbHX60IGjpNkZR9w2/rhZ4...wt2/following.
Code to extract the parent key (put it inside your 1st onDataChange):
String reference = dataSnapshot.getRef().toString();
String[] tokens = reference.split("/");
String parentKey = tokens[tokens.length - 3];
This parentKey should be your houfxWvbwyVmbHX60IGjpNkZR9w2.

How to get particular value using `DataSnapshot` in `Firebase`

I want to get particular value using from DataSnapshot.
I am attaching the screenshot here so kindly check and help me to get particular value from Realtime Database.
Actually I am implementing chat application in which I want to get value of user from group_list.
Here is my code.
private void loadTotalGroupList() {
referenceMainUrl = FirebaseDatabase.getInstance().getReferenceFromUrl("https://pure-coda-174710.firebaseio.com");
referenceGroupList = referenceMainUrl.child("group_list");
//Check if child is available or not.
referenceGroupList.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
Log.e("dataSnapshot"," ==>"+dataSnapshot);
Map<String, Object> newPost = (Map<String, Object>) dataSnapshot.getValue();
Log.e("newPost"," ==>"+newPost);
Log.e("user: ","==>" + newPost.get("user")); // Here I am getting null value
} else {
Log.e("Child not found", " >>>");
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
and log showing like this. DataSnapshot { key = group_list, value = {First Group={-KtBH9gnTszNxcXjNu9A={message=assaasas, user=sakib}}} }

I have resolved my issue by using addChildEventListener
referenceGroupList.addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String prevChildKey) {
Log.e("dataSnapshot KEY", " ==>" + dataSnapshot.getKey());
}
#Override
public void onChildChanged(DataSnapshot dataSnapshot, String prevChildKey) {
}
#Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
#Override
public void onChildMoved(DataSnapshot dataSnapshot, String prevChildKey) {
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
Here dataSnapshot.getKey() returns all sub child of it.

You're listening to the location /group_list in your code. That means a a snapshot from that location will contain the following:
/First Group
/-KtBH9gnTszNxcXjNu9A
message = "..."
user = "..."
If you want to get the user value from that location, you'll have to dig into it using each intermediate path:
dataSnapshot.child("First Group").child("-KtBH9gnTszNxcXjNu9A").child("user").getValue()
Or more simply:
dataSnapshot.child("First Group"/-KtBH9gnTszNxcXjNu9A/user").getValue()
You can't skip the middle paths in the snapshot. Alternatively, you may want to listen to a location closer to the value you want:
referenceMainUrl.child("group_list/First Group/-KtBH9gnTszNxcXjNu9A");

This code runs in a loop and gives you values for all the 'user's
DatabaseReference dRef = FirebaseDatabase.getInstance().getReference().child("group_list").child("First_Group");
dRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot snapshot : dataSnapshot.getChildren()){
String userName = snapshot.child("user").getValue(String.class);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});

Firebase datasnapshot.getValue() returns null

In my app, I have used Firebase database and stored userID in a child and set the value of the child as username to get the username of the current user. Now I'm using addValueEventListener to get the username from the database. This is my Firebase structure.
The code is given below.
checkUsername.child("check").addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
currentUser = dataSnapshot.child(getUserID()).getValue(String.class);
Log.d(TAG, "onDataChange: currentUser = " + currentUser);
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
While debugging, String currentUser returns null.
Screenshot of debugged answer.

Since you have added the valueEventListener at the check node, so getting the child again makes no sense (Because the User ID is the key of check node and not a separate child).
Instead try calling dataSnapshot.getChildren(); directly to get the entire list of updated data and iterate through it to get whatever key value you need.
Something like this,
checkUsername.child("check").addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String prevChildKey) {
String current value = dataSnapshot.getValue(String.class);
Log.d("TAG", "onDataChange: " + current value);
}
#Override
public void onChildChanged(DataSnapshot dataSnapshot, String prevChildKey) {}
#Override
public void onChildRemoved(DataSnapshot dataSnapshot) {}
#Override
public void onChildMoved(DataSnapshot dataSnapshot, String prevChildKey) {}
#Override
public void onCancelled(DatabaseError databaseError) {}
});
Another option in this particular use case is to add a ChildEventListener and get the value inside onChildAdded() method.

How to fetch all data after adding new data in firebase database

This is my code for adding person object in firebase.
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference myRef = database.getReference("Person");
buttonSave.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
String name = editTextName.getText().toString().trim();
String address = editTextAddress.getText().toString().trim();
//Creating Person object
Person person = new Person();
person.setName(name);
person.setAddress(address);
new Firebase(Config.FIREBASE_URL).child("Person").push().setValue(person);
}
});
myRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
//Getting the data from snapshot
Person person = postSnapshot.getValue(Person.class);
//Adding it to a string
String string = "Name: " + person.getName() + "\nAddress: " + person.getAddress() + "\n\n";
//Displaying it on textview
textViewPersons.setText(string);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
System.out.println("The read failed: " + databaseError.getMessage());
}
});
Adding data is working fine and every add creating a new key for person.
But addValueEventListener is showing me only last added entry. I want all the entries data.
Can anyone help me on this?

Every time anything changes in the Person node, you get notified through onDataChange(). In there you loop over the people and then for each call:
textViewPersons.setText(string);
So you're constantly replacing the contents of the text view with the information from each person. After each loop it will end up showing just the information for the last user. You can easily see that the code loops through all people by adding:
System.out.println(string);
With this you'll see each person in logcat, but only the last person in the text view.
One solution is to either use a ListView or RecyclerView, both of which handle lists of items. Another (quicker to implement) way to show all users it to append the strings in the text view:
textViewPersons.setText(textViewPersons.getText()+string+"\n");

Try this if it helps:
String dataviewer=new String();
Firebase firebase=new Firebase(Config.FIREBASE_URL);
buttonSave.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
String name = editTextName.getText().toString().trim();
String address = editTextAddress.getText().toString().trim();
//Creating Person object
Person person = new Person();
person.setName(name);
person.setAddress(address);
new Firebase(Config.FIREBASE_URL).child("Person").push().setValue(person);
}
});
firebase.child("Person").addChildEventListener(new ChildEventListener() {
// Retrieve values as they are added to Firebase
#Override
public void onChildAdded(DataSnapshot snapshot, String previousChildKey) {
Map<String,Object> vals=(Map<String,Object>)snapshot.getValue();
String name_person=String.valueOf(vals.get("name"));
String address_person=String.valueOf(vals.get("address"));
dataviewer+="Name: " + name_person + "\nAddress: " + address_person + "\n\n";
}
#Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
#Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onCancelled(FirebaseError firebaseError) {
}
});