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Retrieved Data from Firebasedatabase and set into recyclierview Adapter

I want to read the data from firebasedatabase and show that into recyclerview retrieve data form FirebaseDatabase by orderbychild method. I want to read data of that child who's email match with my useremail who is currently login from app .
This is my Firebase:
I have successfully completed the first part, but I am facing problems with second part how can I pass the retrieved data to recyclerview adapter.
For example whenever user login from mobeen#gmail.com I read his location and ticket_no and show that data into recyclerview. I am facing problem with this line
programinglist.setAdapter(new myadapter(this, modl1));
where should I pass my modl1 (ArrayList<model> modl1) to recyclerview.setadapter
public class recyclierview extends AppCompatActivity {
public RecyclerView programinglist;
DatabaseReference b1, b2;
public ArrayList<model> modl1;
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_recyclierview);
programinglist = findViewById(R.id.my_recycler_view);
programinglist.setLayoutManager(new LinearLayoutManager(this));
modl1 =new ArrayList<model>();
readdata(new firebasecallback() {
#Override
public void oncallback(ArrayList<model> list) {
Log.v("aliraza" , "value oncalback" + list.get(0).getTicket_no());
}
});
}
private void readdata(final firebasecallback firebasecallback)
{
b1= FirebaseDatabase.getInstance().getReference();
b2=b1.child("tasks");
b2.orderByChild("email").equalTo(MainActivity.email).addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(#NonNull DataSnapshot dataSnapshot, #Nullable String s) {
model m = new model();
String location = dataSnapshot.child("location").getValue().toString();
String tickeno = dataSnapshot.child("ticket_no").getValue().toString();
Log.v("ALI", "family value " +location);
Log.v("ALI", "family value " + tickeno);
m.setLocation(location);
Log.v("ALI", "location " +m.getLocation());
m.setTicket_no(tickeno);
modl1.add(m);
Log.v("ALI", "family value " +modl1.get(0).getTicket_no());
firebasecallback.oncallback(modl1);
}
#Override
public void onChildChanged(#NonNull DataSnapshot dataSnapshot, #Nullable String s) {
}
#Override
public void onChildRemoved(#NonNull DataSnapshot dataSnapshot) {
}
#Override
public void onChildMoved(#NonNull DataSnapshot dataSnapshot, #Nullable String s) {
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
programinglist.setAdapter(new myadapter(this, modl1));// where should i call this setadapter function of recyclierview.enter code here
}
private interface firebasecallback
{
void oncallback( ArrayList<model> list);
}
}

Initialise your arraylist and adapter;
public ArrayList<model> modl1=new ArrayList();
private myadapter adapter;
In onCreate() method initialize your adapter with blank list and set adapter to recyclerview.
adapter=new myadapter(this, modl1);
programinglist.setAdapter(adapter);
then create a method addItem() in your adapter.
public void addItem(model item){
list.add(item); // add item to your adapter list
notifyItemInserted(list.size());
}
changes in onChildAdded() method
modl1.add(m); //remove this line
firebasecallback.oncallback(m);
readdata(new firebasecallback() {
#Override
public void oncallback(model m) {
modl1.add(m);
adapter.add(m);
Log.v("aliraza" , "value oncalback" + list.get(0).getTicket_no());
}
});
You can remove firebasecallback method,as there is no need of it, and directly add item to adapter in onChildAdded() method. Simply call readdata() method from onCreate()
private void readdata()
{
b1= FirebaseDatabase.getInstance().getReference();
b2=b1.child("tasks");
b2.orderByChild("email").equalTo(MainActivity.email).addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(#NonNull DataSnapshot dataSnapshot, #Nullable String s) {
model m = new model();
String location = dataSnapshot.child("location").getValue().toString();
String tickeno = dataSnapshot.child("ticket_no").getValue().toString();
Log.v("ALI", "family value " +location);
Log.v("ALI", "family value " + tickeno);
m.setLocation(location);
Log.v("ALI", "location " +m.getLocation());
m.setTicket_no(tickeno);
modl1.add(m);
Log.v("ALI", "family value " +modl1.get(0).getTicket_no());
adapter.add(m);
}
#Override
public void onChildChanged(#NonNull DataSnapshot dataSnapshot, #Nullable String s) {
}
#Override
public void onChildRemoved(#NonNull DataSnapshot dataSnapshot) {
}
#Override
public void onChildMoved(#NonNull DataSnapshot dataSnapshot, #Nullable String s) {
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
Hope this will help!!

how can i order recyclerview items in firebase by replay timestamps

how can I order my recyclerview items like this
mDatabaseReference = FirebaseDatabase.getInstance().getReference();
productQuery = mDatabaseReference.child("Blog").orderByChild("replaydate");
"replaydate" is located in Replay>psotkey>replaydate I want order blog items by repaydate, is this possiple?

If you want to get the messages by timestamp order you can use
database.orderByChild("replydate").limitToLast(10)
.addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
if (dataSnapshot.getValue() != null) {
Model newModel = dataSnapshot.getValue(Model.class);
//Model is you model which you are using for showing data in recyclerview
arraylist.add(newModel);
adapter.notifyDatasetChanged();
}
#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(DatabaseError databaseError) {
}
});

How to list data from Firebase database to listview? Android

I am trying to create a system where I can enter a reminder into the Android app, have it sent to Firebase to be accessed to all devices with the app, and have that reminder come up on a notification. I still need to make the interface that I can send things to Firebase from the app, but I am having trouble retrieving the data. Right now it doesn't like my listView.setAdapter(arrayAdapter) line because it thinks I am calling a null object reference. This is my code:
public class MainActivity extends AppCompatActivity {
ListView listView;
FirebaseDatabase firebaseDatabase;
DatabaseReference databaseReference;
ArrayList<String> arrayList = new ArrayList<>();
ArrayAdapter<String> arrayAdapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
firebaseDatabase = FirebaseDatabase.getInstance();
databaseReference = firebaseDatabase.getReference("Users");
Toast.makeText(this, "ok", Toast.LENGTH_SHORT).show();
databaseReference.addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
String value=dataSnapshot.getValue(String.class);
arrayList.add(value);
arrayAdapter = new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_list_item_1, arrayList);
listView.setAdapter(arrayAdapter);
}//public void onChildAdded(DataSnapshot dataSnapshot, String s) end
class User {
public String username;
public String email;
public User() {
// Default constructor required for calls to DataSnapshot.getValue(User.class)
}
public User(String username, String email) {
this.username = username;
this.email = email;
}
}//class User end
public void writeNewUser(String userId, String name, String email) {
User user = new User(name, email);
}
#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(DatabaseError databaseError) {
}
});
}//protected void onCreate(Bundle savedInstanceState) end
}
There are some unused classes, but my main question is, Why is the array null? And why does this crash the app when I try to run it on the emulator?
Also, the only things in my database are parent Users and its one child, "goy" (as a test child).

Can't populate listview from firebase database but toast works

I am trying to update a listview realtime from my firebase database. The data uploads to database without any issues and a toast which displays the newly added data also works. But I could not get the listview to work. Here is my code:
public class MainActivity extends AppCompatActivity {
private ListView list;
private Button btnadd;
private EditText ettext;
private DatabaseReference mDatabase;
private ArrayList<String> arrayList= new ArrayList<>();
private ArrayAdapter<String> adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
list=findViewById(R.id.liston);
list.setAdapter(adapter);
btnadd=findViewById(R.id.button);
ettext=findViewById(R.id.ed);
btnadd.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
mDatabase.push().setValue(ettext.getText().toString());
}
});
mDatabase= FirebaseDatabase.getInstance().getReference();
adapter= new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, arrayList);
mDatabase.addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
String string =dataSnapshot.getValue(String.class);
arrayList.add(string);
adapter.notifyDataSetChanged();
Toast.makeText(getApplicationContext(),
"Name: " + dataSnapshot.getValue(), Toast.LENGTH_LONG)
.show();
}
#Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
String string =dataSnapshot.getValue(String.class);
arrayList.remove(string);
adapter.notifyDataSetChanged();
}
#Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
}
The updation of the database also happens from within the app using an "edittext" and a button.

How to get all childs data on ListView - Firebase database

i need to get all data in Childs and show it in ListView
Every Values in Childs!,The main Child is "XXX-Users" and other Childs is about "Model Phones",, i want get All Date of This Childs on ListView
this is my Activity:
public class xxxxxxx extends AppCompatActivity {ListView listView;
ArrayList<String> usernames = new ArrayList<>() ;
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference myRef = database.getReference("xxx-Users");
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.xxxxxxxxxxxxx);
listView = (ListView) findViewById(R.id.listview00);
final ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,usernames);
listView.setAdapter(arrayAdapter);
myRef.addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
String value = dataSnapshot.getValue(String.class);
usernames.add(value);
arrayAdapter.notifyDataSetChanged();
}
#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(DatabaseError databaseError) {
}
});
}`**
My Layout
<ListView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentTop="true"
android:id="#+id/listview00" />

As cricket_007 said, your code doesn't match your data structure. Your listener will fire for the nodes immediately under xxx-Users. But your actual URL values are one level deeper.
One simple way to handler this is to loop over those nested children in onChildAdded():
DatabaseReference myRef = database.getReference("xxx-Users");
myRef.addChildEventListener(new ChildEventListener() {
#Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
String value = childSnapshot.getValue(String.class);
usernames.add(value);
}
arrayAdapter.notifyDataSetChanged();
}
...